Download GCE Chemistry SAMs 2009 onwards pdf

GENERAL CERTIFICATE OF EDUCATION
TYSTYSGRIF ADDYSG GYFFREDINOL
2009 – 2010
CHEMISTRY
SPECIMEN QUESTION PAPERS
SPECIMEN MARKING SCHEMES
GCE CHEMISTRY Specimen Assessment Materials 3
Contents
Page
Question Papers
CH1
5
CH2
23
CH3
35
CH4
55
CH5
69
CH6
78
Mark Schemes
CH1
122
CH2
131
CH4
139
CH5
147
GCE CHEMISTRY Specimen Assessment Materials 5
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Uwch Gyfrannol/Uwch
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
Advanced Subsidiary/Advanced
CHEMISTRY
CH1
SPECIMEN PAPER
(1 hr 30 min)
ADDITIONAL MATERIALS
In addition to this examination paper, you will need a
• calculator
• copy of the Periodic Table supplied by WJEC
INSTRUCTIONS TO CANDIDATES
Answer all questions.
Write your name, centre number and candidate number in the spaces at the top of this page.
Write your answers in the spaces provided in this booklet.
INFORMATION FOR CANDIDATES
The number of marks is given in brackets at the end of each question or part-question.
You are reminded that assessment will take into account the quality of written communication
used in your answers.
No certificate will be awarded to a candidate detected in any unfair practice during the
examination.
GCE CHEMISTRY Specimen Assessment Materials 6
SECTION A
Answer all the questions in the spaces provided.
1.
Complete the following table
Particle
Relative Charge
Relative Mass
proton
+1
1
neutron
no charge
1
1840
electron
[1]
2.
Below are several nuclides of elements
12
6
(a)
C
24
12
Mg
52
24
Cr
73
32
Ge
84
36
Kr
From the above choose
(i)
one element whose atom contains 41 neutrons
[1]
.......................................................................................................................................................
(ii)
two elements whose atoms each have the same number of electrons in the
outer shell
[1]
.......................................................................................................................................................
(b)
1s
↑↓
2s
↑↓
Complete the boxes below, by inserting arrows to represent electrons, to show the
electronic configuration of a chromium atom.
2p
↑↓ ↑↓ ↑↓
3s
3p
3d
4s
[1]
GCE CHEMISTRY Specimen Assessment Materials 7
3.
The diagram below shows part of a radioactive decay series.
State which one of the following best describes the emissions involved in the decay from
238
Pa to 234U.
A
B
C
D
4.
A
B
C
D
1 α-emission and 3 β-emissions
2 α-emissions and 2 β-emissions
3 α-emissions and 1 β-emission
4 α-emissions
………………
[1]
Identify the letter, A, B, C or D, which correctly describes the behaviour of γ radiation.
Behaviour in an electric field
deflected towards the positive electrode
deflected towards the negative electrode
no deflection
no deflection
Relative penetrating power
high
moderate
low
high
[1]
5.
The half life of cobalt, 60Co, used in radiotherapy, is 5.3 years.
Calculate how long it will take for the activity of the isotope to decay to 18 of its original
activity.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 8
6.
State which one of the following gases contains the greatest number of molecules.
A
B
C
D
7.
4 g of hydrogen
11 g of carbon dioxide
16 g of oxygen
28 g of nitrogen
……………
[1]
Naturally occurring chlorine consists of two isotopes and gives a mass spectrum in the
molecular ion region as shown
10
9
8
7
6
relative peak height
5
4
3
2
1
70
(i)
71
72
73
74
mass / charge ratio
75
State the mass numbers of the two isotopes.
76
[1]
.......................................................................................................................................................
(ii)
Give the percentage abundance of each isotope.
[1]
.......................................................................................................................................................
Section A Total [10]
GCE CHEMISTRY Specimen Assessment Materials 9
SECTION B
Answer all the questions in the spaces provided
8.
(a)
Ethanol may be manufactured from ethene and steam by the reaction
CH2=CH2(g) + H2O(g)
CH3CH2OH(g)
ΔHo = –46 kJ mol-1
The manufacturing process involves the use of a heterogeneous catalyst.
(i)
Explain the meaning of the term heterogeneous.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
(ii)
State the effect of the catalyst, if any, on the equilibrium yield of ethanol.
[1]
.......................................................................................................................................................
(iii)
Draw energy profiles for the catalysed and uncatalysed reactions.
[3]
energy
reaction path (extent of reaction)
(b)
Explain, in terms of simple collision theory, why the rate of the reaction in (a) will
increase with an increase in temperature.
[4]
(QWC) [2]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 10
(c)
(i)
Use the standard enthalpy change for the reaction in (a) and the standard
enthalpy change of formation values, ΔH o, given in the table below to
f
calculate the enthalpy change of formation of gaseous ethanol.
Compound
CH2=CH2(g)
H2O(g)
[3]
ΔHfo / kJ mol-1
52.3
–242
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
(ii)
Given that the standard enthalpy change of formation of liquid ethanol is
–248kJmol-1 calculate the enthalpy change for the conversion of one mole of
liquid ethanol to one mole of gaseous ethanol at 298 K.
[1]
.......................................................................................................................................................
Total [15]
GCE CHEMISTRY Specimen Assessment Materials 11
9.
(a)
Andrew carries out an experiment, using the simple apparatus shown below, to find
the enthalpy change of combustion (ΔHc) of ethanol.
draught shield
thermometer
lagged metal container
water
spirit burner
containing ethanol
Here are his results
Mass of ethanol before experiment
Mass of ethanol after experiment
Mass of water
Temperature of water before experiment
Temperature of water after experiment
15.8 g
14.3 g
500 g
20.5 ºC
40.0 ºC
To find the enthalpy change of combustion he uses the equation
ΔH = −
mcΔT
n
where m is the mass of the water in the metal container, c is the specific heat capacity of the
water, ΔT is the temperature rise and n is the number of moles of ethanol burned and he
assumes that c = 4.18 J g-1 K-1 and Mr ethanol = 46.1
(i)
State why the apparatus is shielded from draughts.
[1]
.......................................................................................................................................................
(ii)
State why the mass of water must be known.
[1]
.......................................................................................................................................................
(iii)
State why the metal container holding the water must be very thin and light.
[1]
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 12
(iv)
State why the mass of the ethanol is measured both before and after the
experiment.
[1]
.......................................................................................................................................................
(v)
Calculate the number of moles of ethanol used in the experiment.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
(vi)
Calculate the enthalpy change of combustion (ΔHc) of ethanol, in kJ mol-1.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
(vii)
Give one reason why the value obtained for the enthalpy change in this
experiment is lower than the true value.
[1]
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 13
(b)
Alice obtained the following results when measuring the initial rate of decomposition
of aqueous hydrogen peroxide, as in the following equation.
H2O2 (aq)
concentration of peroxide / mol dm-3
rate / mol dm-3 s-1
H2O (l)
0.100
0.050
+
0.200
0.100
1/2 O2(g)
0.300
0.148
0.400
0.220
0.500
0.250
(i)
Label each axis and, choosing suitable scales for the axes, plot the results on
the grid below and draw the line which best fits the points.
[5]
(ii)
State which main factor needs to remain constant in order to obtain good
results in the experiment.
[1]
.......................................................................................................................................................
(iii)
Suggest a method, other than measuring the concentration of hydrogen
peroxide, that Alice could have used to follow this reaction.
[1]
.......................................................................................................................................................
Total [15]
GCE CHEMISTRY Specimen Assessment Materials 14
10.
(a)
The graph below shows variation of first molar ionisation energy with atomic number
for the elements of atomic number 3 to 11.
first ionisation
energy /
kJ mol-1
3
4
5
6
7
8
9
10
11
atomic number
(i)
Explain why there is a general increase in first ionisation energy from lithium
to neon.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
(ii)
Explain why boron has a lower first ionisation energy than beryllium.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
(iii)
Explain why sodium has a lower first ionisation energy than lithium.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
(iv)
Select the probable second ionisation energy of sodium from the values listed
below.
[1]
247;
700;
988;
4560 kJ mol-1
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 15
(b)
The diagram below shows a part of the atomic emission spectrum of hydrogen.
increasing frequency
Explain why it consists of a series of sharp lines and is not a continuous spectrum. [2]
(QWC) [1]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 16
(c)
Below is a simplified diagram of a mass spectrometer.
(i)
State the sign of the charge on the plates, A, and explain their purpose.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
(ii)
State the function of part B.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
Total [13]
11.
For an industrial process represented by the equilibrium
2A(g) + B(g)
2C(g)
the following data were obtained
Temperature
T/K
600
650
700
750
800
850
900
(a)
(i)
Relative rate of the
forward reaction
logkrel
10.16
10.90
11.59
12.14
12.66
13.11
13.50
Fractional
conversion to C at
equilibrium
f
0.997
0.988
0.967
0.930
0.875
0.798
0.708
Complete the table by filling in the missing values
Product of
logkrel × f
10.13
10.77
11.29
10.46
9.56
[1]
GCE CHEMISTRY Specimen Assessment Materials 17
(ii)
Use the graph grids below to plot the points and draw the curves for
I
the variation of logkrel with T
II
the variation of f with T
III the variation of (logkrel × f) with T
[6]
14.0
1.00
13.0
0.90
log10krel
f
12.0
0.80
11.0
0.70
600
700
800
900
T/K
10.0
600
700
800
900
T/K
12.0
11.0
Product
log10krel×f
10.0
9.0
600
700
800
900
T/K
(b)
State and explain what conclusions may be drawn from the plots in (a) above
concerning the optimal conditions for the production of C.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 18
(c)
State and explain the effect on the position of equilibrium (if any) of increasing the
total pressure.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
(d)
State and explain what can be deduced about the enthalpy change (ΔH) for the
equilibrium.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 19
12.
(a)
Reliable resources of energy need to be available in the future. A UK report
anticipates the differing quantities of fuels needed in 50 years time. In this report
three predictions are made based on different assumptions about future energy supply
and demand. Among the assumptions the following were included:
A
B
C
D
Large new coal deposits can be accessed.
The difficulties surrounding the safe disposal of nuclear waste are resolved.
Many more wind farms are built both on land and off shore.
International agreement on large reductions in carbon dioxide emissions is
reached and is enforced.
The diagram below shows the use of the following energy sources; renewable,
nuclear, coal, oil and gas in 2000 and three predictions for 2057 based on different
possibilities.
250
200
fuel use /
million tonnes 150
of oil
equivalent
100
50
0
2000
gas
prediction
1
oil
prediction
2
coal
prediction
3
nuclear
renewable
For each of the three predictions select one assumption (from A – D above) that
applies to that prediction and explain the reason for your choice.
(i)
Prediction 1.
[2]
Assumption
............................................................................................................................
Reason
............................................................................................................................
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 20
(ii)
Prediction 2.
[2]
Assumption
............................................................................................................................
Reason
............................................................................................................................
.......................................................................................................................................................
(iii)
Prediction 3.
[2]
Assumption
............................................................................................................................
Reason
............................................................................................................................
.......................................................................................................................................................
(b)
The use of hydrogen gas as a fuel to replace petrol is being actively researched by car
manufacturers. Give one advantage and one disadvantage of hydrogen as a car fuel.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
(c)
A major environmental cause for concern in the 21st century is acid rain, which is rain
that is artificially more acidic than normal. One of the main contributors to acid rain
pollution is sulfur dioxide gas, SO2.
(i)
State the meaning of the term acid.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
(i)
Give one reason why the level of atmospheric SO2 is greater in winter than in
summer.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
(ii)
State one problem which is caused by acid rain.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 21
(d)
Sulfur dioxide can be oxidised to sulfur trioxide which dissolves in water to form
sulfuric acid.
In a titration experiment, 21.0 cm3 of sulfuric acid was exactly neutralised by 24.0
cm3 of sodium hydroxide solution of concentration 0.0950 mol dm-3.
The equation for the reaction between aqueous sulfuric acid and aqueous sodium
hydroxide is
H2SO4 + 2NaOH
Na2SO4 + 2H2O
To three significant figures, calculate
(i)
the number of moles of sodium hydroxide used.
[1]
.......................................................................................................................................................
.......................................................................................................................................................
(ii)
the concentration of the sulfuric acid.
[2]
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
Total [14]
Section B Total [70]
GCE CHEMISTRY Specimen Assessment Materials 23
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Uwch Gyfrannol/Uwch
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
Advanced Subsidiary/Advanced
CHEMISTRY
CH2
SPECIMEN PAPER
(1 hr 30 min)
ADDITIONAL MATERIALS
In addition to this examination paper, you will need a
• calculator
• a Data Sheet supplied by WJEC containing a Periodic Table, NMR and IR data
INSTRUCTIONS TO CANDIDATES
Answer all questions.
Write your name, centre number and candidate number in the spaces at the top of this page.
Write your answers in the spaces provided in this booklet.
INFORMATION FOR CANDIDATES
The number of marks is given in brackets at the end of each question or part-question.
You are reminded that assessment will take into account the quality of written communication
used in your answers.
No certificate will be awarded to a candidate detected in any unfair practice during the
examination.
GCE CHEMISTRY Specimen Assessment Materials 24
SECTION A
Answer all the questions in the spaces provided.
1.
(i)
Draw partial charges, if any, on the formula of iodine monochloride below, to
indicate any polarity in this covalent compound.
Explain the reason for your answer.
I
[1]
Cl
........................................................................................................................................
2.
(ii)
Showing outer electrons only, draw a dot and cross diagram for this molecule.
[1]
(i)
Write the balanced equation for the reaction between aqueous strontium ions and
aqueous sulfate ions.
[1]
........................................................................................................................................
(ii)
State what is seen in the reaction in (i) above.
[1]
........................................................................................................................................
3.
State the name of the compound having the skeletal formula.
[1]
OH
.....................................................................
4.
The carbon–bromine bond in 2-bromopropane breaks by heterolytic fission.
structural formulae of the 2-bromopropane and the resulting species.
Write the
[2]
GCE CHEMISTRY Specimen Assessment Materials 25
5.
Part of the formula of an addition polymer is shown below.
CH3
Cl
C
C
H
Cl
n
Write the structural formula of the monomer used to produce this polymer.
6.
[1]
The pheromone of one species of ant is
H
H3C
C
CH3
(i)
C
H
CH2
CH2
C
C
CH2
CH3
H
CH3
C
C
C
CH2
H
State the number of moles of hydrogen gas required to produce one mole of the
corresponding alkane from this pheromone.
[1]
..............................
(ii)
State a suitable catalyst for this hydrogenation.
[1]
..............................
Section A Total [10]
GCE CHEMISTRY Specimen Assessment Materials 26
SECTION B
Answer all the questions in the spaces provided.
7.
(a)
Use the valence shell electron pair repulsion principle (VSEPR) to explain the shape
of a molecule of gaseous born trifluoride, giving the value of the F-B-F bond angle.
[3]
........................................................................................................................................
........................................................................................................................................
(b)
Boron trifluoride reacts with ethoxyethane to give an addition compound containing a
co-ordinate bond between oxygen and boron.
C2 H 5
O
BF3
C2 H 5
(i)
Explain why a co-ordinate bond is formed between oxygen and boron.
[2]
........................................................................................................................................
........................................................................................................................................
(ii)
Apply the VSEPR principle to predict the arrangement of the four bonds
around the central boron atom.
[2]
........................................................................................................................................
........................................................................................................................................
(c)
Magnesium sulfate, an important compound in horticulture, can be made in industry
by reacting the mineral dolomite with dilute sulfuric acid to give calcium sulfate and
magnesium sulfate as two of the products.
(i)
MgCO3.CaCO3
Complete and balance the equation for this reaction.
+
[2]
H2SO4
dolomite
(ii)
Describe what is seen during this reaction.
[2]
........................................................................................................................................
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 27
(iii)
After removal of the calcium sulfate, the solution is heated to increase the
concentration of the magnesium sulfate and then cooled. Crystals of hydrated
magnesium sulfate are then filtered off and dried. The solubility of hydrated
magnesium sulfate at two temperatures is given in the table below.
Temperature / oC
Solubility / g per 100 g of water
20
90
36
123
In a batch process, a saturated solution of magnesium sulfate at 90 oC
contained 200 kg of water.
Use the table to calculate the mass of solid hydrated magnesium sulfate
crystals produced when this solution is cooled to 20 oC.
[2]
Mass produced ………………. ……kg.
Total [13]
8.
(a)
Chloroethanoic acid can be made by reacting ethanoic acid with chlorine in the
presence of ultraviolet light. This reaction is similar to the reaction of methane with
chlorine. Part of a possible mechanism for this reaction is shown below.
Initiation stage
Propagation stages Cl
+ CH3COOH
CH2COOH
(i)
2Cl
Cl2
+ Cl2
CH2COOH + HCl
ClCH2COOH + Cl
State the function of ultraviolet light in the initiation stage.
[1]
........................................................................................................................................
(ii)
Use the propagation stages to give the overall equation for the reaction.
[1]
........................................................................................................................................
(iii)
Use the stages of the mechanism above to write a termination stage for the
reaction.
[1]
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 28
(b)
Describe a test to show the presence of a C-Cl bond in chloroethanoic acid. Your
answer should state the reagent(s) required after hydrolysing the C-Cl bond by
heating the acid with excess of an alkali. State what is seen after adding the
reagent(s).
[3]
Reagent(s) ……………………………………………………………………………
........................................................................................................................................
Observation …………………………………………………………………………..
(c)
5-Chloropentanoic acid, ClCH2CH2CH2CH2COOH, used as a plant growth hormone,
can be made from pent-4-enoic acid.
H
H2C
C
CH2 CH2 COOH
pent-4-enoic acid
(i)
State whether or not pent-4-enoic acid can exist as E-Z geometric isomers,
explaining your choice of answer.
[1]
........................................................................................................................................
........................................................................................................................................
(ii)
Addition of hydrogen chloride to pent-4-enoic acid gives the two compounds
4-chloropentanoic acid and 5-chloropentanoic acid.
I
State the type of reaction mechanism occurring when hydrogen halides such
as hydrogen chloride or hydrogen bromide add to compounds containing
C=C bonds.
[2]
........................................................................................................................................
II
The mechanism for this reaction involves the carbocations A and B.
H
CH2
C
(CH2)2COOH
+
carbocation A
CH(CH2)3COOH
+
carbocation B
Use these carbocations to explain why the preferred product of the reaction is
4-chloropentanoic acid.
[2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 29
(d)
Dichlorodifluoromethane was formerly used as a refrigerant, but its use is not now
allowed as it has been found to deplete ozone in the upper atmosphere.
Explain why dichlorodifluoromethane causes this effect but 1,1,1-trifluoroethane does
not affect the ozone layer.
[2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(e)
The boiling temperatures of two fluorinated compounds are shown in the table.
Name
Formula
Boiling temperature / oC
1,1,1-trifluoroethane
CF3CH3
– 47
2,2,2-trifluoroethanol
CF3CH2OH
78
Explain, in terms of intermolecular forces, why the boiling temperatures of these two
compounds are so different.
You are advised to use a diagram in your answer.
[3]
(QWC) [1]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Total [16]
GCE CHEMISTRY Specimen Assessment Materials 30
9.
(a)
The industrial preparation of ethanol using ethene is a vitally important process.
Describe how ethanol can be made, in two stages from decane, C10H22.
Your answer should
• give any necessary conditions for both stages,
• contain an equation for the second stage leading to ethanol,
• name the products / reactants in each stage.
[6]
(QWC) [2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(b)
There is considerable interest in the biochemical synthesis of organic compounds that
were previously made from oil.
One method for producing butan-1-ol is by fermenting sugar residues by a particular
micro-organism. The three main products from this fermentation are ethanol,
butan-1-ol and propanone. These liquid products are then separated by fractional
distillation.
(i)
Chemists are interested in developing this process but the present yield of
products is low.
State and explain two variables that you would recommend changing to
increase the yield of products.
[4]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 31
(ii)
You are given the three main products of fermentation in separate unlabelled
bottles.
I
Describe how you would use infrared spectroscopy to identify which of the
three liquids was propanone,
[2]
H3C
C
CH3
O
propanone
........................................................................................................................................
........................................................................................................................................
II
Describe how you would identify the two remaining liquids by the use of a
physical property, explaining why the liquids differ in this physical property.
[2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Total [16]
10.
(a)
The diagram shows the structure of graphite
(i)
Describe the bonding in graphite.
[2]
........................................................................................................................................
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 32
(ii)
Describe the hardness and electrical conductivity of graphite and explain
these in terms of the structure.
[2]
Hardness ……………………………………………………………………..
............................................................................................................................
Electrical conductivity …………………………………………..……………
............................................................................................................................
(iii)
Describe the structure of a carbon nanotube and relate this to the structure of
graphite.
[2]
........................................................................................................................................
........................................................................................................................................
(b)
Nano-sized particles are very small, typically less than 100 nm across.
At this scale the properties of materials change drastically from those of larger
particles.
Give an example of the use of nanoparticles.
[1]
........................................................................................................................................
(c)
(i)
Solid calcium oxide, CaO, has the same crystal structure as sodium chloride.
Draw a labelled diagram which shows the crystal structure of calcium oxide
and gives the formulae of its ions.
State the crystal co-ordination numbers of the ions present.
[3]
(ii)
One method of making pure calcium is to heat calcium oxide with aluminium
at a high temperature.
3CaO
+
2Al
Al2O3
+
3Ca
By use of oxidation states (numbers) explain why this is a redox reaction. [2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 33
(d)
Describe what is seen when calcium metal is added to water and pH indicator is
added to the resulting mixture.
[3]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Total [15]
11.
(a)
Bromine combines with reactive metals such as sodium giving sodium bromide,
which contains sodium and bromide ions.
(i)
Explain why there is a tendency for a bromine atom to become a bromide ion.
[1]
........................................................................................................................................
........................................................................................................................................
(ii)
You are provided with a solution that contains colourless bromide ions.
State what is seen when chlorine gas is passed into the solution, giving an
ionic equation for the reaction that occurs.
[2]
Observation ...............................................................................................
............................................................................................................................
Ionic equation ………………………………………………………………...
(b)
An organic compound, X, containing carbon, hydrogen and bromine, was formerly
used as a pesticide.
(i)
Analysis of compound X showed that it had a relative molecular mass of
94.9.
Use the information given to deduce the molecular formula of compound X.
[3]
(ii)
The use of compound X was discontinued after it was found that it caused
damage to the ozone layer in the upper atmosphere.
A major use for compound X was as a fumigant. Vapours of compound X
were allowed to circulate in a grain warehouse. This vapour killed insects
and rodents that would eat the grain.
Residual vapour was then removed by extractor fans before the grain was
removed.
Scientists need to choose another organic compound in place of compound X.
GCE CHEMISTRY Specimen Assessment Materials 34
Suggest two features, apart from cost and possible ozone damage, that the
compound should possess if it is to be used as a fumigant in this way.
[2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(c)
When ethene is bubbled into dilute bromine water, one of the products is
2-bromoethanol.
Describe how you would confirm that the compound is likely to be 2-bromoethanol,
by use of infrared and mass spectroscopy.
Bromine consists of two isotopes 79Br and 81Br in equal quantities.
[2]
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Total [10]
Section B Total [70]
GCE CHEMISTRY Specimen Assessment Materials 35
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Uwch Gyfrannol/Uwch
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
Advanced Subsidiary/Advanced
CHEMISTRY
CH3
EXEMPLAR INTERNAL ASSESSMENT TASKS
Candidates are expected to complete two internal assessment tasks of a standard exemplified here.
These may be completed at any time up to the submission date and must be completed under the
supervision of a qualified chemistry teacher who will need to verify all readings taken by each
candidate. The tasks are taken from quantitative analysis and stoichiometry, thermochemistry or
kinetics.
Centres may devise their own tasks, subject to approval of the task and the associated mark scheme by
the WJEC. Criteria for devising these internal assessment tasks are given in the specification.
Alternatively, centres may use the WJEC exemplars, two of which are shown here.
GCE CHEMISTRY Specimen Assessment Materials 36
UNIT 3.1 (AS) - Candidate Instruction Sheet
A Study of Energy Changes - the indirect determination of the enthalpy change of reaction of
magnesium oxide with carbon dioxide to form magnesium carbonate by thermochemical
measurement and Hess’s law
Introduction
Millions of tons of chemicals are reacted each year, not to form a product but to obtain energy from
chemical reactions. Most of these involve the combustion of hydrocarbons and other fuels by the
oxygen in air. Measurements of the energy liberated in such reactions are very important but require
the use of bomb calorimeters and oxygen under pressure which makes them unsuitable for advanced
level work in schools.
However the principles involved can be readily seen by using quieter and more easily controlled
reactions such as the one you are to carry out. As well as measuring the heat liberated and calculating
the enthalpy changes for your reactions, you will be able to use your values to find the enthalpy
change for a reaction that cannot be measured directly.
Aim
Your aims in this exercise are;
(a)
(b)
(c)
(d)
to gather information and plan your work with due regard to safety considerations,
to carry out the experiment,
to calculate, analyse and evaluate your results, and
to answer the questions in the proforma relating to the experiment.
Background Information
You are to measure the enthalpy changes of reaction of magnesium oxide and of magnesium
carbonate with dilute hydrochloric acid. By applying Hess’s law to your results you will be able to
calculate the enthalpy change above, which is difficult to measure directly, as shown in the cycle
given below.
MgO(s) + CO2(g)
2H+
ΔH3
MgCO3(s)
2H+
ΔH1
ΔH2
Mg2+(aq) + H2O(l) + CO2(g)
The method involves carrying out the reactions in separate experiments in insulated calorimeters,
calculating the heat evolved - correcting for heat losses to the surroundings - and scaling up to molar
amounts of the solids used.
GCE CHEMISTRY Specimen Assessment Materials 37
Apparatus and chemicals
You will need safety goggles, a thermometer graduated in 0.2 or 0.5 degree divisions (or a digital
thermometer), a simple calorimeter, a 50 cm3 burette and a weighing bottle. You are provided with a
suitable quantity of dry magnesium oxide, dry magnesium carbonate and 2 mol dm-3 hydrochloric
acid.
You will need to weigh out accurately about 0.90 g of magnesium oxide (i.e. between 0.85 and 0.95
g) for the first measurement and 3.5 g of magnesium carbonate (i.e. between 3.40 and 3.60 g) for the
second. It will be appropriate to use 50 cm3 of dilute hydrochloric acid in any experiment you
perform: the acid must be in excess.
Safety Considerations
No special precautions are necessary for spillage of the solids. If large quantities are involved, mix
with sand to sweep up.
If you splash any of the hydrochloric acid onto your skin, notify your supervisor and wash the
affected area with copious water.
Should you break a mercury-in-glass thermometer, try to retain the liquid mercury. The vapour is very
poisonous, with cumulative effects. If necessary, droplets of mercury can be sucked up using a small
aspirator and pump. If mercury is spilled into floor cracks, the volatility can be reduced by brushing in
sulfur or zinc dust.
At the end of the experiment, small quantities of the chemicals can be diluted with running water and
run to waste.
Procedure
After absorbing all the information available to you, write a plan, which will enable you to determine,
as accurately as possible, the required enthalpy change of reaction of magnesium oxide with carbon
dioxide to form magnesium carbonate. After having your plan checked by the teacher, carry out the
experiment according to the plan and plot appropriate temperature/time graphs for any sets of data.
Analysis of Results
1. Calculate the heat evolved in each case.
This equals the corrected temperature rise (ΔT) × the mass of acid (water) heated (50 g) × the
heat capacity of this acid (water) (4.18 J g-1). [ΔT is positive if T increases]
2. This heat was for the mass of metal oxide or carbonate used, so scale up to 1 mol of
oxide or carbonate to obtain the molar enthalpy change for the reactions (ΔH1 and ΔH2).
3. Study the energy cycle given and see that the required enthalpy change (ΔH3 ) equals ΔH1 minus
ΔH2.
GCE CHEMISTRY Specimen Assessment Materials 38
Conclusion, Evaluation and Question
1.
Estimate the precision in your values and record your three enthalpy change values with a
number of significant figures, which corresponds with your estimate. Comment on their values
and signs.
2.
How do the signs of the temperature changes relate to the signs of the enthalpy values
calculated for your two experiments?
Allocation of marks
The 30 available marks for this experiment are allocated in the following manner:
Planning [5]; Implementing [15]; Analysing [5]; Evaluating [5].
GCE CHEMISTRY Specimen Assessment Materials 39
Experiment 3.1 (AS) - Technical Advice Notes for Teachers and Technicians
Indirect determination of the enthalpy change of reaction of magnesium oxide with carbon
dioxide to form magnesium carbonate by thermochemical measurement and Hess’s law
The apparatus, chemicals and solutions required are listed below.
Universally available items may not be listed.
Each student will require:
safety goggles
thermometer graduated in 0.2 / 0.5 degree divisions / digital
simple calorimeter
50 cm3 burette
2 mol dm-3 hydrochloric acid
dry magnesium oxide
dry magnesium carbonate
The masses of the solids to be used are governed to some extent by the thermometers or other
temperature measurers used. If 0.5 rather than 0.2 degree divisions are used, larger temperature
changes are preferable to increase precision, even though this will increase the heat loss correction.
Probably about 0.9 g of magnesium oxide and 3.5 g of carbonate would represent a suitable
compromise, giving temperature changes of around 10 degrees while still having excess acid, which is
necessary to ensure rapid and complete reaction. In general, to optimise precision, temperature
changes of around 10 degrees should be aimed for and a burette should be used to measure the acid
volume since errors using measuring cylinders can be substantial.
Note:
Only one determination is required for each of the reactions, i.e. a total of two runs.
Magnesium carbonate is available in light (magnesia alba levis) or heavy (magnesia alba ponderosa)
forms. It has been reported that some light material may be lost from the liquid due to frothing, so
that it is better, if possible, to use the heavy version.
Similarly the heavy form of magnesium oxide is preferred if there is a choice.
The purchased carbonate is likely to be a basic carbonate: this has no effect on the experiment but
means that the calculated final enthalpy change may not match the literature value. Marks are,
however, based on the teacher’s value and not that in the literature.
GCE CHEMISTRY Specimen Assessment Materials 40
ASSESSMENT UNIT 3.1 SUMMER 200…..
Centre Name ………………………………………………Centre Number ……………………
Candidate’s Name …………………………………………Candidate’s Number ………………
Proforma for Expt. 3.1
Enthalpy change of reaction of magnesium oxide with carbon dioxide to form
magnesium carbonate
(Attach another sheet, in the appropriate position, if you need more space)
Plan
Before proceeding to carry out your plan you must have the plan checked by your teacher.
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
………………………………………………………………………..........................................
[2]
GCE CHEMISTRY Specimen Assessment Materials 41
Questions
1.
Write a balanced equation for the combustion of methane gas.
[1]
………………………………………………………………………………………………………
2.
Calculate the mass of carbon dioxide produced when one mole of propane is completely
combusted.
[1]
…………………………………………………...……………………………………………………
…………………………………………………………………...……………………………………
3.
Suggest a possibly useful combustion reaction that does not form carbon dioxide.
[1]
……………………………………………………………………...…………………………………
Results
1.
MgO + acid
mass container + MgO =
……………….. g
mass container
=
……………….. g
=
……………….. g
mass container
=
……………….. g
∴ mass MgCO3
=
……………….. g
∴ mass MgO
Temperature/time table
The thermometer used was graduated in …………… degree divisions.
[state thermometer precision here ]
2.
MgCO3 + acid
mass container + MgCO3 =
Temperature/time table
……………….. g
GCE CHEMISTRY Specimen Assessment Materials 42
Analysing Results
(show your working in the calculations)
1.
MgO Please restate mass of MgO used
……………..g
maximum temperature if no heat lost = ………………..
initial temperature = ……………….
temperature change = ……………….
Calculation of heat change in expt.
……………………………………………………………………………………..………..……………
……………………………………………………………………………..……………..………………
……………………………………........................…………………………………...………….............
…………………………………………………………………………………………………................
Calculation of ΔH1
……………………………………………………………………………………..………………..……
……………………………………………………………………………..………………………..……
…………………………………………………………………………………...………………….……
…………………………………………………………………................................................................
2.
MgCO3 Please restate mass of MgCO3 used
………………g
maximum temperature if no heat lost = ………………..
initial temperature = ……………….
temperature change = ……………….
Calculation of heat change in expt.
……………………………………………………………………………………..…………..…………
………………………………………………………………………..………………………..…………
……………………………………………………………………….……...............................................
………………………………………………………………………………………………...........….....
GCE CHEMISTRY Specimen Assessment Materials 43
Calculation of ΔH2
……………………………………………………………………………………..……………….……
……………………………………………………………………………..…………………….………
…………………………………………..……………………………………….....................................
………………………………………………………………………………………..........………….....
Calculation of ΔH3 , the enthalpy change for the reaction
……………………………………………………………….………………………………………...…
……………………………………………………………………………………………………………
…………………………………………………………………..……......................................................
………………………………………………………………………………………………................
Evaluation and question
Include (a) your estimate of the precision of your results and a consequent restating your results to a
sensible number of significant figures, and
(b) a statement of how the signs of the temperature changes relate to the signs of the
enthalpy values calculated in the two experiments.
…………………………………………………………………………………………..……….………
…………………………………………………………………………………..……….………………
……………………………………………………………………………………………………………
……………………………………………………………………….…………..………………….……
……………………………………………………………………………………………………………
…………………………………………………….……………..………………………………….……
…………………………………………….………………………………………………………...……
………………………………………………………………....................................................................
[2]
GCE CHEMISTRY Specimen Assessment Materials 44
Question
Motor vehicle environmental effects are judged on the grams of carbon dioxide emitted per kilometre
of travel.
The combustion equations for bioethanol and the alkane ethane and the energy liberated are
and
C2H5OH + 3O2
2CO2 + 3H2O, Δ H = –1371 kJ mol-1
C2H6
2CO2 + 3H2O, Δ H = –1560 kJ mol-1.
+
7
2
O2
Bearing in mind that the car is driven by the energy liberated, state which fuel would be more
environmentally friendly per mol on the basis of these results, giving your reason.
There is, however, another factor to be considered. Discuss this and state whether or not your initial
conclusion should be altered.
[3]
…………………………………………………………………………………………..……….………
…………………………………………………………………………………..……….………………
……………………………………………………………………………………………………………
……………………………………………………………………….…………..………………….……
……………………………………………………………………………………………………………
…………………………………………………….……………..………………………………….……
…………………………………………….………………………………………………………...……
………………………………………………………………....................................................................
……………………………………………………………………….…………..………………….……
……………………………………………………………………………………………………………
…………………………………………………….……………..………………………………….……
…………………………………………….………………………………………………………...……
………………………………………………………………....................................................................
Remember that any graphs must be attached to your work.
Allocation of marks
The 30 available marks for this experiment are allocated in the following manner:
Planning [5]; Implementing [15]; Analysing [5]; Evaluating [5].
GCE CHEMISTRY Specimen Assessment Materials 45
Experiment 3.2 (AS) – Candidate Instruction Sheet
A Group and/or Individual Study of the Kinetics of a Chemical reaction
Introduction
We may write equations for chemical reactions easily enough but how quickly do they actually occur,
if at all? Our bodies, for example, should burn up in the oxygen of the air but fortunately do not. We
can turn on the gas but nothing happens until we apply a spark.
Thus the rate at which reactions take place, or kinetics, is of great practical importance - in industry
and the environment as well as in the laboratory. Also by studying kinetics we can find out the actual
mechanism of the chemical change and thus make it more efficient such as by developing suitable
catalysts.
For this exercise we choose the reliable and attractive experiment below which can be performed by
an individual student or partly as a group exercise to widen its scope.
Aim
Your aims in this exercise are;
(a)
to gather information and plan your work,
(b)
to carry out the experiment,
(c)
to calculate, analyse and evaluate your results, including combining your results with those of
other members of your group if the exercise is run as a group experiment, and
(d)
to answer the questions in the proforma relating to the experiment.
Kinetics of the oxidation of iodide ion by hydrogen peroxide in acid solution using a clock
method
Background Information
Iodide ions are oxidised to iodine by hydrogen peroxide in acidic solutions at a measurable rate.
Iodine gives a strongly coloured blue complex with starch solution but if a given amount of
thiosulfate ion - with which iodine reacts very rapidly - is added, no blue colour will appear until
enough iodine has been formed to react with all the thiosulfate. The time taken for this to occur thus
acts as a “clock” to measure the rate of the H2O2/HI reaction. By varying the concentrations of the
reactants, such as peroxide, one at a time and measuring the rate, as above, the dependence of rate on
concentration (this is called the order of reaction) for any reactant may be found. The relevant
equations are,
H2O2
I2
+
+
2HI
2S2O32−
slow
fast
2H2O
2I − +
+
I2
S4O62−
GCE CHEMISTRY Specimen Assessment Materials 46
Apparatus and chemicals
You will need safety goggles, a stopwatch or stopclock, pipettes and fillers, burettes and funnel, a
conical flask or beaker, test tubes and a stirring rod. The solutions provided are
0.1 mol dm-3 hydrogen peroxide, 1 mol dm-3 sulfuric acid, 0.1 mol dm-3 potassium iodide,
0.005 mol dm-3 sodium thiosulfate and starch solution.
Safety Considerations
If you splash any of the sulfuric acid onto your skin, notify your supervisor and wash the affected area
with copious water. Any spillage should be diluted with water before being mopped up.
At the concentrations involved the other chemicals (hydrogen peroxide, potassium iodide, sodium
thiosulfate, starch and the iodine formed) present minimal hazards.
Note that hydrogen peroxide is not stable over long periods and should be prepared freshly. If a
concentrated solution is used as the stock and diluted down as required, be aware that solutions more
concentrated than 1.5 mol dm-3 ("20 volume") can act as irritants or even be corrosive.
At the end of the experiment, small quantities of the chemicals can be diluted with running water and
run to waste.
GCE CHEMISTRY Specimen Assessment Materials 47
Procedure
After absorbing all the information available to you, write a plan, which will enable you to study the
kinetics of this reaction as accurately as possible. The plan must be checked by the teacher before
proceeding with the experiment.
First perform a trial run to find out which ranges of concentrations will be suitable for your plan. All
runs can be at room temperature but make sure that this is constant since rates vary rapidly with
changes in temperature.
For the trial run mix 10 cm3 of sulfuric acid, 10 cm3 of thiosulfate, 15 cm3 of KI, 1 cm3 of starch
solution and 9 cm3 of deionised water, get ready with the stopwatch and rapidly add 5.0 cm3 of
peroxide which you have previously measured into a dry test tube, simultaneously starting the watch
and mixing thoroughly. Once the solution is well-mixed there is no need to stir any more.
Observe carefully, stop the watch immediately the blue colour appears and record the time.
Now plan a set of five similar runs which each differ only in the peroxide concentration in the
mixture, balancing the amount of water added so that the total volume is again 50 cm3. Bearing in
mind the time taken for the trial run, vary the amount of peroxide used by as much as practicable
ensuring that runs are neither too short nor too long: each run is carried out in exactly the same way.
Construct a table showing the volumes of reactants used in each run and record the time taken for the
blue colour to appear.
Details for Group Component
If this is included each member of the group will carry out the procedure above using a different
volume of iodide ion but keeping the total volume the same. Group members will then compare their
rates at a given peroxide concentration, obtained from their graphs produced as below and thus find
the effect of changing the iodide concentration on the rate.
Other possibilities are to find the effect of changing the acid concentration in the same way or to carry
out the runs at different temperatures to find the effect on the rate.
Analysis
In each run the time taken for the blue colour to appear is inversely proportional to the rate of reaction
( the slower the rate the longer it will take for the fixed amount of reaction to occur). In all your runs
only the concentration of peroxide is different so that by comparing the times taken for the runs you
will be able to see how the concentration of peroxide affects the rate of reaction.
Since the rate is inversely proportional to the time taken, this is best done by plotting a graph of
(1/time) against peroxide concentration. Also since the total volume is constant in each case [H2O2] is
directly proportional to the volume of peroxide used in each run so that you can just plot (1/time) s-1
versus volume of peroxide.
If a straight line results this shows that the rate is directly proportional to [H2O2].
Conclusion, Evaluation and Questions
From your plot decide how the peroxide concentration affects the rate.
Estimate how precise your results are and state the main source of error.
Answer the questions on the proforma.
GCE CHEMISTRY Specimen Assessment Materials 48
Allocation of marks
The 30 available marks for this experiment are allocated as follows:
Planning [5]; Implementing [15]; Analysing [5]; Evaluating [5].
GCE CHEMISTRY Specimen Assessment Materials 49
Experiment 3.2 - Technical Advice Notes for Teachers and Technicians
Kinetics of the oxidation of iodide ion by hydrogen peroxide in acid solution using a clock
method
The apparatus, chemicals and solutions required are listed below.
Universally available items may not be listed.
Each student will require:
safety goggles
stopwatch / stopclock
pipettes and fillers
burettes and funnels
conical flask / beaker
test tubes
stirring rod
0.1 mol dm-3 hydrogen peroxide
1 mol dm-3 sulfuric acid
0.1 mol dm-3 potassium iodide
0.005 mol dm-3 sodium thiosulfate
starch solution
GCE CHEMISTRY Specimen Assessment Materials 50
ASSESSMENT UNIT 3.2 SUMMER 200…..
Centre Name …………………………………
……………Centre Number ……………………
Candidate’s Name …………………………………………Candidate’s Number ………………
Proforma for Expt. 3.2
Kinetics of oxidation of iodide by hydrogen peroxide in acid
(Attach another sheet, in the appropriate position, if you need more space)
Plan
Before proceeding to carry out your plan you must have the plan checked by your teacher.
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
………………………………………………………………………...............................................……
[2]
GCE CHEMISTRY Specimen Assessment Materials 51
Questions
1.
State why it is essential that all your runs are with the same total volume of liquid.
[1]
………………………………….......……………………………………………………………………
2.
Explain the roles of the thiosulfate and starch in the way that this rate is measured.
[2]
…………………………………………………………………….……………………………….……
………………………………………………………………………………………………...…….......
GCE CHEMISTRY Specimen Assessment Materials 52
Results
Trial run
Volumes used
Time to blue colour
Runs varying peroxide concentration
(table of volumes and times for numbered runs)
GCE CHEMISTRY Specimen Assessment Materials 53
Analysing results
(show sample of working)
Calculation of 1/time for each run
………………………………………………………………..………………..…………………………
………………………………………………………………………………………………....................
Table of peroxide volumes and 1/time for graph
Result from attached graph
………………………………………………………………………………..………………….………
………………………………………………………………………………………………...................
………………………………………………………………………………………………….........…..
How does the rate depend on the concentration of peroxide?
………………………………………………………………………………..………………….………
………………………………………………………………………………………………...................
[1]
GCE CHEMISTRY Specimen Assessment Materials 54
Evaluation
(a)
Give an estimate of how precise your experiment was and state the largest source of error.
(b)
Suggest an improvement to the method.
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………
……………………………………………………………………………................................................
[2]
Question
3.
The formation of highly oxidising peroxides is dangerous to living cells and enzymes such as
catalase have evolved to destroy them. Briefly summarise an experiment that you would
design to study the kinetics of the decomposition of hydrogen peroxide solutions to oxygen
and water by catalase powder.
[3]
………………………………………………………………………………………........…………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
………………………………………………………………………………………………………
Remember that your graph must be attached to your work
Allocation of marks
The 30 available marks for this experiment are allocated in the following manner:
Planning [5]; Implementing [15]; Analysing [5]; Evaluating [5].
GCE CHEMISTRY Specimen Assessment Materials 55
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
Advanced Subsidiary/Advanced
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Uwch Gyfrannol/Uwch
CHEMISTRY
CH4
SPECIMEN PAPER
(1hr 45min)
ADDITIONAL MATERIALS
In addition to this examination paper, you will need
• a calculator
• an 8 page answer book
• a Data Sheet supplied by WJEC containing a Periodic Table, NMR and IR data
INSTRUCTIONS TO CANDIDATES
Answer all questions.
Write your answers to Section A in the spaces provided in this booklet.
Write your answers to Section B in the 8 page answer book provided.
Write your name, centre number and candidate number in the spaces at the top of this page.
INFORMATION FOR CANDIDATES
The number of marks is given in brackets at the end of each question or part-question.
You are reminded that assessment will take into account the quality of written communication
used in your answers.
No certificate will be awarded to a candidate detected in any unfair practice during the
examination.
You are reminded that this paper contains synoptic questions and so will test understanding of the
connections between the different elements of the subject.
GCE CHEMISTRY Specimen Assessment Materials 56
SECTION A
Answer the questions in the spaces provided.
1.
(a)
Cis-hex-3-enal is responsible for the smell of cut grass.
CH3CH2CH=CHCH2CHO
cis-hex-3-enal
(i)
Both aldehydes and ketones react with 2,4-dinitrophenylhydrazine.
I.
State the type of reaction that is occurring.
[1]
...............................................................................................................................
II.
State what is seen when an aldehyde reacts with 2,4-dinitrophenylhydrazine.
[1]
...............................................................................................................................
III.
This reaction can be used to identify a particular aldehyde by taking the
melting temperature of the product and comparing the value with the book
value. If the product obtained in this reaction, using cis-hex-3-enal is
impure, state the effect this will have on the expected melting temperature.
[2]
...............................................................................................................................
(ii)
Give the molecular formula of cis-hex-3-enal.
[1]
...............................................................................................................................
(b)
Another isomer of cis-hex-3-enal is hex-5-en-2-one.
H2C
CH
CH2
CH2
C
CH3
O
hex -5-en-2-one
(i)
This compound undergoes the triiodomethane (iodoform reaction).
I.
State the reagents used ………………………………………………….. [1]
II.
State what is seen as the result of this test……………….………………
[1]
GCE CHEMISTRY Specimen Assessment Materials 57
(ii)
Describe a chemical test, other than (i) above, which can be used to
distinguish between cis-hex-3-enal and hex-5-en-2-one.
[2]
Reagent(s) used ………………………………………………..……...……..
Observation with cis-hex-3-enal …………………………...…………………
Observation with hex-5-en-2-one ……………………………………………..
(c)
Under suitable conditions, cis-hex-3-enal can be obtained by oxidising the alcohol,
cis-hex-3-en-1-ol.
If the infrared spectrum of both compounds was taken, state how the absorptions due
to the O-H and C=O bonds would differ in the two compounds.
[2]
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(d)
A sample of hex-2-enal is in contact with an aqueous solution of sodium carbonate
and left in the air.
After some time bubbles of carbon dioxide appear.
hex-2-enal
sodium carbonate solution
State the class of organic compound responsible for this reaction and the type of
reaction necessary to produce it from hex-2-enal.
[2]
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 58
2.
(a)
(b)
Chlorobenzene can be made in the laboratory from benzene and chlorine gas.
Give the equation for this reaction and state the catalyst used.
[2]
In industry, chlorobenzene is made by passing benzene vapour, hydrogen chloride
and air over a solid copper chloride catalyst.
Cl
(g)
+
HCl (g)
+
(g)
1/2 O2 (g)
+
H2O(g)
The products are cooled, giving chlorobenzene and water as immiscible liquids.
(i)
State one advantage of the industrial method compared to the laboratory
method.
[1]
...............................................................................................................................
...............................................................................................................................
(ii)
State how you would separate a mixture of chlorobenzene and water.
[1]
...............................................................................................................................
(c)
Although there are problems in using the insecticide DDT, it is still used in a number
of countries.
It is made by reacting together chlorobenzene and trichloroethanal, in the presence of
a catalyst.
H
2
Cl
+
CCl3CHO
Cl
C
Cl
Cl
+
H2O
C Cl
Cl
(i)
State why chemists see this reaction as one with high atom economy.
[1]
.........................................................................................................................................
........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 59
(ii)
Explain why, when DDT is boiled with aqueous sodium hydroxide,
I.
the chlorine atoms bonded to the aliphatic carbon atom are removed,
[1]
.........................................................................................................................................
.........................................................................................................................................
II.
the chlorine atoms bonded to the benzene rings are not removed.
[1]
.........................................................................................................................................
.........................................................................................................................................
(d)
DDT is a fat soluble material and is not easily biodegradable.
Methoxychlor, a development of DDT is a polar molecule and, being more water
soluble, can be excreted more easily.
H
C
H3C O
Cl
C
Cl
OCH3
Cl
Methoxychlor
Suggest how the presence of oxygen in the methoxy groups, CH3O, enables the
compound to hydrogen bond with water molecules.
[1]
.........................................................................................................................................
.........................................................................................................................................
(e)
(i)
Halogenated derivatives of phenols are used as antiseptics.
State how 2,4,6-tribromophenol can be made from phenol, describing what is
seen.
[2]
Reagent(s) ………………………………………………………....…………..
Observation(s) ………..……………………………………………….………
GCE CHEMISTRY Specimen Assessment Materials 60
Dettol is made from 3,5-dimethylphenol (Mr 122).
(ii)
Cl
H3C
CH3
OH
3,5-dimethylphenol
H3C
CH3
OH
Dettol
Calculate the relative molecular mass of Dettol and hence the theoretical yield of
Dettol, starting from 1.00 kg of 3,5-dimethylphenol.
[2]
Total [12]
GCE CHEMISTRY Specimen Assessment Materials 61
3.
Read the passage below and then answer the question in the spaces provided.
Food additives and their analysis
The demand for a wide range of foods throughout the year has meant an increasing number of
additives being added to food. These are meant to ensure that that the food will be an acceptable
colour, to preserve the food against bacterial of fungal attack and to prevent oxidation.
The European Commission allows certain food additives to be used and most of these have an E
number. Even so, there is considerable discussion about the safety and the advisability of using some
of these additives.
A bottle of dilutable lime juice contains, among other additives, citric acid and sodium citrate as
acidity regulators, sodium saccharin and aspartame as sweeteners together with copper complexes of
chlorophyllins and carotenes as colouring agents.
HO
H2C
COOH
C
COOH
H2C
COOH
Citric acid
HOOC
CH2
NH2 O
H
CH2 O
CH
N
CH
C
C
O
CH3
Aspartame
The separation of large molecule food additives from a mixture presents a challenge to the analytical
chemist. High performance liquid chromatography (HPLC) has been shown to be effective in a
number of separations, but one problem is the detection of individual compounds after separation has
occurred. If the separated materials are coloured then detection is straightforward. However, many
compounds have no colour but they do absorb in the ultraviolet region. If the solvent used does not
absorb in the ultraviolet then detection may be possible using an ultraviolet lamp of a suitable
frequency.
After separation of the mixture into its individual components, confirmation of the compounds can be
carried out using, for example, mass spectroscopy, NMR and chemical tests.
A HPLC chromatogram of a mixture of food additives is shown on the next page.
GCE CHEMISTRY Specimen Assessment Materials 62
1
3
4
5
2
0
5
6
10
15
20
retention time / min
Key
number
compound
1
4-hydroxybenzenecarboxylic acid
2
sorbic acid
3
benzenecarboxylic acid
4
methyl 4-hydroxybenzenecarboxylate
5
ethyl 4-hydroxybenzenecarboxylate
6
1-propyl 4-hydroxybenzenecarboxylate
The safety and usage of a number of food additives remains questionable, and the separation and
analysis of the many differing compounds in mixtures of prepared foods presents a significant task for
those engaged in this work.
- End of passage -
GCE CHEMISTRY Specimen Assessment Materials 63
(a)
Citric acid is prepared biochemically by the fermentation of sugar beet residues using
certain fungi. During this process, calcium sulfate is produced as a waste product.
Not all the sugar is converted to citric acid and the filtrate containing organic residues
is treated anaerobically to produce methane, which is used as a fuel in the
manufacture of citric acid.
(i)
In a trial using a new variety of fungus, a solution containing 20.6 kg of
sucrose (Mr 342) from sugar beet was fermented.
At the end of the fermentation, the mass of citric acid (Mr 192) obtained was
5.20 kg.
Assuming that the theoretical yield of citric acid from 1 mole of sucrose is
also 1 mole, calculate the percentage yield of citric acid obtained.
[2]
(ii)
Suggest two factors that should be considered, apart from cost, when
deciding if this new variety of fungus should be adopted for the manufacture
of citric acid.
[2]
1.
…………………………………………………………………………………
………………………………………………………………………………………….
2.
…………………………………………………………………………………
………………………………………………………………………………………….
(b)
Aspartame is a dipeptide formed between the methyl ester of the α-amino acid, 2aminophenylpropanoic acid, and aspartic acid.
CH2
H2N
C
H
O
C
O H
2-aminophenylpropanoic acid
(i)
Write the structural formula
2-aminophenylpropanoic acid.
for
the
zwitterion
form
of
[1]
GCE CHEMISTRY Specimen Assessment Materials 64
(ii)
Write the structural formula for aspartic acid.
[1]
(iii)
Aspartic acid contains a chiral centre.
Explain why a solution of equimolar amounts of both optical isomers is
apparently optically inactive.
State the name give to this equimolar mixture.
[3]
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(c)
The HPLC chromatogram of the food additive mixture shows that it contains
benzenecarboxylic acid, C6H5COOH, and 4-hydroxybenzenecarboxylic acid.
You are given separate samples of these two acids, dissolved in a suitable solvent.
State a chemical reagent that will distinguish between these two acids, giving the
result of the test in each case.
[2]
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(d)
The chromatogram also shows the presence of sorbic acid (hex-2,4-dienoic acid),
CH2-CH=CH-CH=CH-COOH.
Explain why hex-2,4-dienoic acid can exist as several different geometrical (E-Z)
isomers.
[2]
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
(e)
The chromatogram also shows the presence of three esters of the compound
4-hydroxybenzenecarboxylic acid. These absorb strongly in the ultraviolet region
and have been suggested for use in sunscreen creams.
State two variables that should be kept constant when scientists are comparing the
effectiveness of these three esters in absorbing ultraviolet radiation.
[2]
1. ...............................................................................................................................
2. ...............................................................................................................................
Section A Total [40]
GCE CHEMISTRY Specimen Assessment Materials 65
SECTION B
Answer both questions in the separate answer book provided.
4.
(a)
Poly(phenylethene) is made in industry from ethylbenzene by passing it over a hot
catalyst and then polymerising the product, phenylethene.
CH2CH3
CH
CH2
+
ethylbenzene
H2
polymerisation
poly(phenylethene)
(i)
Alkylbenzenes such as ethylbenzene and 1-butylbenzene can be made by a
Friedel-Crafts reaction at room temperature.
Describe how 1-butylbenzene can be produced in this way in the laboratory,
using benzene as one of the reactants.
You should give necessary reactants, essential conditions and an equation. [5]
(ii)
The product in (i), 1-butylbenzene, has a boiling temperature of 183 oC.
It is contaminated by a small quantity of 2-butylbenzene, which has a lower
boiling temperature of 173 oC.
Comment on the type and relative strength of the bonding forces between
molecules that causes these compounds to have different boiling
temperatures.
[3]
(iii)
In the industrial preparation of ethylbenzene it is possible to obtain small
quantities of 1,4-diethylbenzene as a by-product.
CH2CH3
CH2CH3
Explain why the low resolution NMR spectrum of this compound consists of
only three peaks.
[2]
GCE CHEMISTRY Specimen Assessment Materials 66
(iv)
(b)
The production of phenylethene from ethylbenzene is an example of an
elimination reaction.
Give another example of an elimination reaction, stating the reactants,
conditions and products or giving an equation.
[3]
Ethanol is a vitally important organic compound that can be used by itself or as a
feedstock in making other compounds. A major industrial preparation of ethanol is
the hydration of ethene at 300 oC and 60 atmospheres pressure.
Describe how a sample of ethanol (boiling temperature 78 oC) can be made in the
laboratory, starting from bromoethane. Your answer should give
•
•
•
•
•
the reactants
any essential conditions,
the type of reaction occurring,
an equation,
the method for obtaining a sample of ethanol from the reaction mixture.
Suggest one reason, other than cost, for the ethene route being preferred by industry
to the method that you have described.
[5]
(QWC) [2]
Total [20]
5.
(a)
A book stated that ‘the commonest reactions of benzene involve electrophilic
substitution’.
Explain why this statement is true and illustrate your answer by drawing the
mechanism for the formation of nitrobenzene, C6H5NO2, starting from benzene and
the nitronium ion.
[5]
(b)
In 2005, a number of foods in Britain were found to contain the banned red
colouring agent, Sudan 1.
N
N
OH
Sudan 1
(i)
Sudan 1 can be made by coupling benzenediazonium chloride with an
alkaline solution of naphthalen-2-ol.
Describe how nitrobenzene can be converted into phenylamine and then how
phenylamine can be used to produce benzenediazonium chloride.
In each stage, you should state the reagents used and any essential
conditions. Chemical equations are not required.
[5]
GCE CHEMISTRY Specimen Assessment Materials 67
(ii)
(c)
Azo dyes such as Sudan 1 contain a chromophore.
State the meaning of this term and explain why Sudan 1 is red in white light
but appears black when blue light is shone upon it.
[4]
The addition of an acid chloride to water gives a solution where all the chlorine is
present as chloride ions.
If an excess of silver ions are added to this solution, silver chloride is precipitated.
This is then filtered off and its mass found.
In an experiment, 2.50 g of an acid chloride R-COCl, where R is an alkyl group, was
added to water. An excess of silver ions were added and the resulting silver chloride
(Mr 143.5) had a mass of 3.87 g.
Use this information to find the molecular formula of the acid chloride.
[5]
(QWC) [1]
Total [20]
Section B Total [40]
GCE CHEMISTRY Specimen Assessment Materials 69
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
Advanced Subsidiary/Advanced
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Uwch Gyfrannol/Uwch
CHEMISTRY
CH5
SPECIMEN PAPER
(1hr 45min)
ADDITIONAL MATERIALS
In addition to this examination paper, you will need
• a calculator
• an 8 page answer book
• a Periodic Table supplied by WJEC
INSTRUCTIONS TO CANDIDATES
Answer all questions.
Write your answers to Section A in the spaces provided in this booklet.
Write your answers to Section B in the separate answer book provided.
Write your name, centre number and candidate number in the spaces at the top of this page.
INFORMATION FOR CANDIDATES
The number of marks is given in brackets at the end of each question or part-question.
You are reminded that the quality of written communication used in your answers will be
important in accessing the marks allocated, especially where the letters QWC appear at the end of
a question.
No certificate will be awarded to a candidate detected in any unfair practice during the
examination.
You are reminded that this paper is synoptic and so will test understanding of the connections
between the different elements of the subject.
GCE CHEMISTRY Specimen Assessment Materials 70
SECTION A
Answer all the questions in the spaces provided.
1.
(a)
Explain the term dynamic equilibrium.
[1]
.........................................................................................................................................
.........................................................................................................................................
(b)
At a given fixed temperature, for the reaction
N2(g)
+
3H2(g)
2NH3(g)
the equilibrium constant, Kc, = 0.50 mol2 dm-6.
(i)
Write an expression for Kc.
(ii)
If 2.0 mol of nitrogen gas and 4.0 mol of hydrogen gas are in equilibrium
with ammonia in a 2.0 dm3 flask at this temperature,
I
find the equilibrium concentration of ammonia, NH3, in mol dm-3,
[1]
[2]
.........................................................................................................................................
.........................................................................................................................................
II
calculate the percentage of the total nitrogen in the system present as N2 gas
at equilibrium.
[2]
.........................................................................................................................................
.........................................................................................................................................
(c)
Measurements on the rate of the reaction
2NO(g)
+ Cl2(g)
2NOCl(g)
showed that when the partial pressure of NO, pNO, was doubled at constant partial
pressure of chlorine, pCl2, the initial rate of reaction increased by a factor of 4 and the
initial rate of reaction increased by a factor of 8 when the partial pressures pNO and
pCl2 were both doubled.
(i)
Deduce the order of reaction with respect to NO.
[1]
.........................................................................................................................................
.........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 71
(ii)
Deduce the order of reaction with respect to Cl2.
[1]
.........................................................................................................................................
.........................................................................................................................................
(iii)
Deduce the overall order of the reaction.
[1]
.........................................................................................................................................
.........................................................................................................................................
(iv)
(d)
Given that the forward reaction is thought to occur in a single step, draw in
the space below the most likely transition state for the reaction.
[2]
Consider the effect of a temperature increase and the addition of a catalyst on the
properties of a reaction by inserting increase (I), decrease (D), or no effect (NE) in the
table.
[2]
Property of the reaction
Activation energy of the
forward reaction
The rate of the forward
reaction
Temperature increase
Addition of a catalyst
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 72
2.
(a)
(i)
Describe the action of chlorine on aqueous sodium hydroxide, giving the
appropriate reaction conditions and writing a balanced equation for each
reaction which occurs.
[4]
.........................................................................................................................................
.........................................................................................................................................
.........................................................................................................................................
.........................................................................................................................................
.........................................................................................................................................
(ii)
Illustrate the variable oxidation states of chlorine by giving two species from
your answer to (a)(i) in which chlorine has different oxidation states. Give the
appropriate oxidation states.
[2]
.........................................................................................................................................
.........................................................................................................................................
.........................................................................................................................................
(b)
(i)
Explain why lead forms a stable Pb2+ ion but carbon does not form a
corresponding C2+ ion.
[2]
.........................................................................................................................................
.........................................................................................................................................
.........................................................................................................................................
(ii)
For each of the following, describe the observation(s) and write balanced
equations for the reactions occurring:
I excess sodium hydroxide solution is added to a solution containing Pb2+(aq) ions;
[3]
.........................................................................................................................................
.........................................................................................................................................
II potassium iodide is added to a solution containing Pb2+(aq) ions.
[2]
.........................................................................................................................................
.........................................................................................................................................
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 73
3.
Read the passage below and then answer the questions (a) to (f) in the spaces provided.
Ethanoic acid is a typical carboxylic acid, which has been known for thousands of
years. The common name for ethanoic acid is acetic acid, a name derived from the
Latin for vinegar, acetum.
Ethanoic acid is a weak acid in aqueous solution. (Ka = 1·78 x 10–5 mol dm–3 at 298
K). An equilibrium exists in aqueous solution and the equation representing this is:
5
H3O+(aq) + CH3COO–(aq)
CH3COOH(aq) + H2O(1)
Traditionally, ethanoic acid was determined by titration against alkali using the
colour change of an indicator to find the end point. Today, to allow automation of the
process, the titration is often performed by using a pH meter connected to a computer
to find the end-point.
10
When a strong acid such as hydrochloric acid is titrated against alkali such as sodium
hydroxide, there is a jump of 8 to 10 pH units at the end-point, and the pH at the endpoint is 7. For a weak acid titrated against sodium hydroxide, the pH jump is smaller
and the end-point pH is usually in the range 8 to 9.
An aqueous solution containing equimolar amounts of ethanoic acid and sodium
ethanoate, CH3COO–Na+, acts as a buffer solution.
15
A dilute solution of the acid is used as vinegar. A typical domestic brown malt
vinegar is labelled as 5% acidity, that is, 5 g of acid per 100 cm3 of solution.
The annual world production of ethanoic acid is in excess of six million tonnes per
year. To meet world demand, modern production methods have been devised, for
example, the direct combination of carbon monoxide and methanol at moderate
temperature (450 K) and pressure (30 atm) with a rhodium-iodine catalyst. This
exothermic reaction gives a yield of over 99%, whereas earlier processes produced up
to 40% of by-products.
Most of the ethanoic acid manufactured is converted into other useful substances
such as esters (flavourings, solvents etc.), cellulose ethanoate (rayon fibres) and PVA
(adhesives). Very little of it ends up on chips!
20
25
– End of passage –
(a)
Explain the term weak acid.
[1]
.........................................................................................................................................
.........................................................................................................................................
(b)
Write the expression for the acid dissociation constant, Ka , of ethanoic acid,
CH3COOH. (line 6).
[1]
Ka
=
GCE CHEMISTRY Specimen Assessment Materials 74
(c)
The dissociation constant, Ka, for benzenecarboxylic (benzoic acid) is
6·31 × 10–5 mol dm–3 at 298 K.
State, giving a reason, whether ethanoic acid is a stronger or weaker acid than benzoic
acid (line 4).
[1]
.........................................................................................................................................
.........................................................................................................................................
(d)
The pH titration curves shown below are for the titration of 20.0 cm3 of aqueous acid
with aqueous NaOH of concentration 0.100 mol dm-3;
Volume of 0.100 mol dm-3 NaOH /cm3
With brief reasons (lines 11-14) ,
(i)
give the number of the titration curve which represents hydrochloric acid v
sodium hydroxide,
[2]
.........................................................................................................................................
.........................................................................................................................................
(ii)
give the number of the titration curve which represents ethanoic acid v
sodium hydroxide,
[2]
.........................................................................................................................................
.........................................................................................................................................
(iii)
state the number of the titration in which the most concentrated acid was
used,
[2]
.........................................................................................................................................
.........................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 75
(iv)
calculate the concentration of the acid in (iii).
[2]
.........................................................................................................................................
.........................................................................................................................................
(e)
Explain what is meant by a buffer solution (line 16).
[1]
.........................................................................................................................................
.........................................................................................................................................
(f)
Calculate the concentration, in mol dm–3, of ethanoic acid in brown malt vinegar
(lines 17-18).
[2]
.........................................................................................................................................
.........................................................................................................................................
Total [14]
GCE CHEMISTRY Specimen Assessment Materials 76
SECTION B
Answer both questions in the separate answer book provided.
4.
(a)
Group 3 (group 13) compounds are often electron deficient. Discuss the reasons for
the existence of electron deficient compounds and the reactions which can remove
this deficiency. Your answer should include
•
•
•
•
(b)
(c)
an explanation of electron deficiency in compounds
the dimerisation of aluminium chloride
donor- acceptor compounds
complex anions.
[5]
(QWC) [2]
(i)
Describe the structure of hexagonal boron nitride and compare it to the
structure of graphite.
[3]
(QWC) [1]
(ii)
Explain how this structure is modified to form nanotubes
[1]
(iii)
State one industrial use of boron nitride.
[1]
One method of making boron nitride is the reaction of boron(III) oxide with
ammonia:
B2O3(s)
+
2NH3(g)
2BN(s) + 3H2O(g)
Given the following values,
Enthalpy change of formation
ΔH o
/ kJ mol-1
Entropy
S
/J mol-1 K-1
B2O3(s)
–1272.8
54.0
NH3(g)
– 46.1
192.3
BN(s)
–254.4
14.8
H2O(g)
–241.8
188.7
Compound
f
(i)
calculate the enthalpy change, ΔHo, for the reaction,
(ii)
determine, showing all reasoning, whether the reaction will occur at a
temperature of 600 ºC,
[3]
(iii)
explain why the entropy values for B2O3 and BN are much lower than those
for NH3 and H2O.
[2]
[2]
Total [20]
GCE CHEMISTRY Specimen Assessment Materials 77
5.
(a)
Four standard electrode potentials (A to D) are listed below.
Eo /V
Half equation
A Cr2O72– + 14H+
+ 6e–
B O2 + 4H+ + 4e–
C Fe3+ + e–
D 2H+
(b)
+ 2e–
2Cr3+ + 7H2O
2H2O
Fe2+
H2
+1.33
+1.23
+0.77
0
(i)
Explain why potential D has a value of zero.
[2]
(ii)
Use A and C to show that acidified dichromate oxidises iron(II) to iron(III)
and write a balanced equation for the reaction.
[2]
(iii)
If a student titrated three 25.0 cm3 samples of a solution containing Fe2+ ions
against a standard 0.0200 mol dm-3 potassium dichromate solution, obtaining
titres of 26.00 cm3 , 26.05 cm3 and 26.50 cm3 respectively, calculate the
concentration of the Fe2+ solution in mol dm-3 to three significant figures.
[2]
(iv)
If the Fe2+ solution was prepared by dissolving ammonium iron(II) sulfate
crystals, (NH4)2Fe(SO4)2.6H2O, in water, calculate the concentration of
ammonium iron(II) sulfate in g dm-3.
[2]
(v)
Use B and C to explain why Fe2+ ions are not stable in water containing
dissolved air.
[2]
(vi)
Explain how B and D form the basis of a hydrogen fuel cell.
(vii)
State one advantage and one disadvantage of using hydrogen fuel cells as a
source of power and heat.
[2]
(i)
State the full electron subshell configurations for the Fe2+ ion and explain
why iron is able to form more than one stable cation.
[3]
(ii)
State the shapes of the [Fe(H2O)6]2+ and [FeCl4]– complex ions, which are
based on the same shapes as the corresponding copper(II) complexes.
[2]
[3]
Total [20]
GCE CHEMISTRY Specimen Assessment Materials 78
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
Advanced Subsidiary/Advanced
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Uwch Gyfrannol/Uwch
CHEMISTRY
CH6
EXEMPLAR INTERNAL ASSESSMENT TASKS
Candidates are expected to complete two internal assessment tasks of a standard exemplified here.
These may be completed at any time up to the submission date and must be completed under the
supervision of a qualified chemistry teacher who will need to verify all readings taken by each
candidate.
The tasks must be selected so that:
•
one is an inorganic chemistry assessment and the other is an organic chemistry assessment;
•
one has a substantial planning element, the other does not, e.g., for the exemplars shown here,
I1 can be combined with O2 or I2 combined with O1, but not I1 with O1 or I2 with O2.
Centres may devise their own tasks, subject to approval of the task and the associated mark scheme by
the WJEC. Criteria for devising these internal assessment tasks are given in the specification.
Alternatively, centres may use the WJEC exemplars, four of which are shown here.
GCE CHEMISTRY Specimen Assessment Materials 79
UNIT 6 Experiment I1 – Candidate Instruction Sheet
Synthesis and Analysis in Chemistry - the stoichiometry of iron(II) ethanedioate hydrate
Introduction
Synthesis and analysis are the two major branches of chemistry. Millions of tons of chemical
compounds and materials are synthesised each year to serve our needs. These must of course be
analysed for purity but analysis is important in its own right in studies of our environment, our health,
forensic science, etc., etc.
The purpose of this experiment is to synthesise a chemical compound and then to analyse it by finding
its relative molecular mass and thus determine the number of molecules of water of crystallisation in
the molecule, x.
Aim
(a)
(b)
(c)
(d)
Study the information provided and plan your course of action.
Carry out the synthesis.
Analyse your product and thus find the number of water molecules in your compound.
Evaluate your work by answering the associated questions.
Background Information
Synthesis
When a solution containing Fe2+ ions is treated with a slight excess of a solution containing
ethanedioate ions, C2O42–, a bright yellow solid is precipitated. This compound is iron(II)
ethanedioate hydrate, which may be written as FeC2O4.xH2O.
Analysis
The compound reacts in acidic solution, at about 70 °C, with potassium manganate(VII), KMnO4,
ions. From the amount of standard MnO4− solution
which reacts with both Fe2+ and C2O42–
required for a given mass of the iron(II) ethanedioate hydrate the Mr value of the latter may then be
determined and hence the value of x.
GCE CHEMISTRY Specimen Assessment Materials 80
Theory
1.
Standardisation of the potassium mangante(VII):
Fe2+ vs MnO4−
Since MnO4− + 8H+ + 5e → Mn2+ + 4H2O
and
Fe2+ – e → Fe3+,
it follows that MnO4− ≡ 5 Fe2+,
i.e. that one mole of MnO4– reacts with five moles of Fe2+,
so that
m1 v1 = 5 m2 v2 where m1 and m2 are the concentrations of Fe2+, and MnO4−
respectively, and v1 and v2 the corresponding volumes used.
Hence m2 = m1 v1/5v2
2.
Titration of the prepared ethanedioate hydrate against the standardised potassium
manganate(VII) solution: FeC2O4 vs MnO4−
Since ethanedioate ion reacts according to
C2O42– – 2e → 2CO2
combination of this with
Fe2+ – e → Fe3+
and with
MnO4− + 8H+ + 5e → Mn2+ + 4H2O
gives the result
MnO4− + 5FeC2O4 + 24H+ → 5Fe3+ + 3Mn2+ + 10CO2 + 12H2O ………. A
or, more simply, that three moles of MnO4− react with five moles of FeC2O4, the water of
crystallisation present in the latter playing no part in the redox process.
Hence
MnO4− ≡ 5FeC2O4
Thus, if a sample of W(g) of the iron(II) ethanedioate hydrate requires a volume
v (cm3) of MnO4− solution of concentration m (mol dm-3),
then the number of moles of MnO4− reacting is mv/1000 and
this number of moles will react with 5mv/3000 moles of FeC2O4.xH2O.
Hence
W/Mr = 5mv/3000
so that
Mr = 600W/mv
Moreover, since
then
Mr = 143⋅87 + 18⋅02x,
x = (Mr – 143⋅87)/18⋅02
Apparatus and reagents
You are provided with safety goggles and standard volumetric glassware i.e. a 50 cm3 burette and
funnel, a 25 cm3 pipette and filler, 250 cm3 conical flasks, and a 250 cm3 graduated flask.
You are provided also with a suitable quantity of iron(II) ammonium sulfate-6-water,
Fe(NH4)2(SO4)2.6H2O. In addition you are given suitable solutions containing Fe2+ and C2O42– ions
for the preparation of the iron(II) ethanedioate hydrate and appropriate filtration apparatus. Also
available is an approximately 0⋅02 mol dm-3 solution of potassium manganate(VII).
GCE CHEMISTRY Specimen Assessment Materials 81
Safety Considerations
All ethanedioates are toxic. You should wear gloves and eye protection when handling the sodium
ethanedioate solution and gloves when manipulating the solid product. Inform your supervisor
immediately if you swallow ethanedioate or splash it onto skin or eyes. At the end of the experiment
any surplus ethanedioates may be destroyed with acidified potassium manganate(VII) and warm water
and then mixed with a large amount of water and run to waste.
Propanone is highly flammable and should not be used near flames or sources of heat.
Potassium manganate(VII) stains skin and clothes: in the event of splashes wash with water. (Stains
on skin or clothes may be removable with small quantities of dilute hydrogen peroxide.)
Procedure
To 50 cm3 of a solution of 0⋅2 mol dm-3 iron(II) ammonium sulfate-6-water add a slight excess of 0⋅2
mol dm-3 sodium ethanedioate solution, with steady stirring. Allow the solid precipitated to settle
and test the supernatant liquid with a few drops of the ethanedioate solution to ensure complete
precipitation. Filter the precipitate through a sintered glass crucible, wash with a little propanone, and
suck as dry as possible at the pump. Carefully dry the solid at 100 °C for use in the next stage.
(If a sinter is not available, a small Büchner or Hirsch funnel may be used instead.)
Meanwhile, prepare a standard solution of iron(II) ammonium sulfate-6-water (Mr 392·16) by
weighing accurately (to 3 or 4 decimal places) about 9⋅8 g of the solid and dissolving the same in
water, using a 250 cm3 graduated flask. Use your solution of iron(II) ammonium sulfate-6-water to
standardise the approximately 0⋅02 mol dm-3 solution of potassium manganate(VII), with which you
have been supplied. The required titrations should be carried out in acid solution, using dilute sulfuric
acid.
Then weigh out accurately (to 3 or 4 decimal places) three separate (and labelled) samples of the
iron(II) ethanedioate hydrate into conical flasks, using about 0·2 g. of the prepared solid in each case.
Remember that the hydrate is toxic and care is required to avoid spillage.
(Note than an error of ± 0⋅005 g in 0⋅200 g amounts to 2⋅5 % and would lead to a titre error of
more than ± 0⋅8 cm3.) To each sample add about 25 cm3 of about 2⋅0 mol dm-3 dilute sulfuric acid and
warm the contents to about 70 °C before titration against your standardised potassium manganate(VII)
solution.
[For each sample of around 0⋅2 g the titre at the end point should lie in the region of 30 to 35 cm3.]
(It is important here, to avoid drifting end points, that the temperature be maintained at close to 70 °C
(or above) during the titration, so as to ensure complete reaction of the ethanedioate ion. Since the
total volume of liquid in the flask is immaterial, this may be effected by the addition, from time to
time, of boiling water, if necessary.)
Analysis, Evaluation and Questions
Record your results and calculations on the proforma and answer the questions in the proforma.
Allocation of marks
The 30 marks available for this experiment are allocated as follows:
Planning [5]; Implementing [15]; Analysing [5]; Evaluating [5]
GCE CHEMISTRY Specimen Assessment Materials 82
ASSESSMENT UNIT 6 I1 SUMMER 200…..
Centre Name ………………………………………………Centre Number ……………………
Candidate’s Name …………………………………………Candidate’s Number ………………
Proforma for Expt. I1
The stoichiometry of iron(II) ethanedioate hydrate
(Attach further sheet(s), in the appropriate position if you need more space)
Plan
.............................................................................................................................................................
.............................................................................................................................................................
.............................................................................................................................................................
.............................................................................................................................................................
.............................................................................................................................................................
[2]
GCE CHEMISTRY Specimen Assessment Materials 83
1. Preparation of iron (II) ethanedioate hydrate
Quality of sample (assessed by teacher for appearance and dryness)
[2]
2. Results and Calculations for the Standardisation of KMnO4
Mass of container plus Fe(NH4)2(SO4)2.6H2O
......................... g
Mass of container less some Fe(NH4)2(SO4)2.6H2O
......................... g
Mass of Fe(NH4)2(SO4)2.6H2O used
......................... g
Volume of graduated flask used.
....................... cm3
Concentration of standard Fe(NH4)2(SO4)2.6H2O solution
…………………………………………………………………………………….……
……………………………………………………………………………... mol dm-3
[1]
Titrations
Titre 1
Titre 2
Titre 3
Titre 4
Initial burette reading /cm3
Final burette reading /cm3
Volume of KMnO4 /cm3
Volume of pipette used .................................... cm3
Note: no more than four titrations should be necessary to obtain consistent results – tick
(9) those titre values used in obtaining your average.
Average KMnO4 solution titre value .................................... cm3
[4]
GCE CHEMISTRY Specimen Assessment Materials 84
Calculation
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
Hence concentration of KMnO4 solution ............................... mol dm-3
[1]
GCE CHEMISTRY Specimen Assessment Materials 85
3.
Results and Calculations for the Relative molecular mass, Mr, of
FeC2O4.xH2O and hence the value of x
Results
Sample 1
Sample 2
Sample 3
Mass of container plus compound /g
Mass of container less some compound /g
Mass of compound used /g
Initial burette reading /cm3
Final burette reading /cm3
Volume of KMnO4 solution used /cm3
[3 × 3]
Calculations
(i)
Carry out separate calculations to determine the mass/titre ratio for each sample,
reporting your results in the table below. (Theory Section (W / v)) Note that the
three mass/titre values should not be averaged, and that the answers in (ii) and (iii)
below should similarly be reported separately for the three samples.
Sample 1
Sample 2
Sample 3
Ratio Mass/Titre / g cm-3
(ii)
Calculate the relative molecular mass, Mr, of the hydrate, and hence
(iii)
the value of x, the number of moles of water of crystallisation in one mole of the
hydrate.
[1]
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
[2]
GCE CHEMISTRY Specimen Assessment Materials 86
Questions
1.
Write down the initial and final oxidation states (numbers) of both the iron and manganese
species in the equation marked (A) in part 2 of the theory section.
[1]
......................................................................................................................................................
2.
State why no indicator is needed to find the endpoint.
[1]
......................................................................................................................................................
3.
Explain why the standardisation is carried out at room temperature while the ethanedioate
titration is done at 70 degrees.
[1]
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
4.
Suggest which of these two titrations is likely to be the more accurate, giving a reason.
[1]
......................................................................................................................................................
......................................................................................................................................................
5.
Estimate the precision in the determination of Mr for the hydrate.
[1]
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
6.
Explain why the percentage error in x will be larger than that in Mr.
[1]
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 87
7.
Assess the advantages and disadvantages of making up 250 cm3 of the ethanedioate
solution and titrating separate 25 cm3 portions of this compared with the method that you
actually used.
[2]
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 88
ASSESSMENT UNIT 6 I1
TEACHER RESULTS SHEET
200 . . .
Centre Name: ……………………………………..… Centre Number: …………………
This form should be completed, as appropriate, by the subject teacher and accompany
the work of the candidate(s) sent for assessment.
Experiment I1
The stoichiometry of iron(II) ethanedioate hydrate
1.
Standardisation of KMnO4
Titre 1
Titre 2
Titre 3
Titre of KMnO4 / cm3
Mass of Fe(NH4)2(SO4)2.6H2O used ......................................... g
Concentration of Fe(NH4)2(SO4)2.6H2O .................................. mol dm-3
Average of titre value used ................................................ cm3
Concentration of KMnO4 .......................................................... mol dm-3
Calculation
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
GCE CHEMISTRY Specimen Assessment Materials 89
2.
Mr of FeC2O4.xH2O
Sample 1
Sample 2
Sample 3
Mass of compound used / g
Titre of KMnO4 / cm3
Mass/Titre Ratio / g cm-3
Mr
x
Calculations
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
Signed: .........................................................................Date:......................................................
(Subject Teacher)
GCE CHEMISTRY Specimen Assessment Materials 90
Experiment I.1 - Technical Advice Notes for Teachers and Technicians
The stoichiometry of iron(II) ethanedioate hydrate
The apparatus and reagents required are listed below.
Universally available items may not be included.
Each student will require:
•
•
•
•
•
•
•
•
•
•
safety goggles
50 cm3 burette
burette funnel
25cm3 pipette
pipette filler
250 cm3 conical flasks
250 cm3 graduated flask
approximately 0⋅02 mol dm-3 KMnO4 solution (to be standardised)
about 10 g of iron(II) ammonium sulfate-6-water, Fe(NH4)2(SO4)2.6H2O
solutions (about 0⋅2 mol dm-3 in each case) of iron(II) ammonium sulfate-6-water and of
sodium ethanedioate, for the preparation of the title compound
•
250 cm3 beakers
•
sintered glass crucible (or Büchner or Hirsch funnel) and Büchner flask
•
dilute sulfuric acid (approximately 2 mol dm-3)
•
weighing bottle
•
propanone
Safety Considerations
Note that all ethanedioates are toxic.
Sodium ethanedioate is harmful when in contact with the skin or when swallowed. Strong solutions
(> ca. 0⋅3 mol dm-3) can cause burns. If swallowed give water, but do not induce vomiting. Seek
medical advice. If splashed in the eyes, flood with water for 10 minutes and seek medical advice.
If spilt, mop up with mineral absorbent. To dispose of excess, run to waste with a large amount of
water.
Potassium manganate(VII)
If splashed into the eyes flood with water for 10 minutes and seek medical advice. If swallowed, give
water and seek medical attention.
Propanone
Propanone can cause degreasing of the skin and eye damage. For any large spillages, shut off all
sources of ignition, open windows, apply mineral absorbent and sweep up.
GCE CHEMISTRY Specimen Assessment Materials 91
UNIT 6 Experiment O1 – Candidate Instruction Sheet
Organic Synthesis, "Green" Chemistry and Atom
benzenecarboxylic acid by oxidation of a primary alcohol
Economy
-
the
synthesis
of
Introduction
Organic synthesis is of vital importance to the modern world in making plastics, drugs, dyestuffs,
chemicals for agriculture, etc. At the same time there is an increasing realisation that syntheses must
be carried out with as little waste of materials and energy as possible and without harming the
environment; in other words making chemistry "green". Ideally then, synthesis should be carried out
at room temperature and pressure and this is where enzyme-catalysed reactions are important.
A useful concept in green chemistry is that of atom economy; this gives the percentage of the mass of
the atoms in the reactant molecules that finish up in the product, based on the stoichiometric equation.
For example, 1-bromobutane may be synthesised by adding HBr to
1-butene with 100% atom economy or by reacting butan-1-ol with PBr3 with an atom economy of
83% as seen by the relevant equations:
C4H8 + HBr
C4H9Br
and 3C4H9OH + PBr3
Aim
(a)
3C4H9Br + H3PO3
To study the information provided and plan your course of action.
(b)
To synthesise benzenecarboxylic acid by an oxidation reaction and carry out physical and
chemical tests on the product.
(c)
To calculate the percentage yield and evaluate factors affecting the yield.
(d)
To calculate the percentage atom economy in your synthetic method and compare this with that
in an alternative, given, method of synthesis.
(e)
To answer questions related to the exercise.
Outline
Both primary and secondary alcohols, of general formulae RCH2OH and R1R2CH(OH) respectively,
readily undergo oxidation reactions with a variety of reagents. In the case of primary alcohols the
oxidation can sometimes be arrested at the intermediate stage of the aldehyde, RCHO, but complete
oxidation to the carboxylic acid, RCOOH, more often occurs. On the other hand, for secondary
alcohols, oxidation leads only to the single product of the ketone, R1R2CO.
In this investigation the primary alcohol phenylmethanol (benzyl alcohol), C6H5CH2OH, on oxidation
produces solid benzenecarboxylic acid (benzoic acid).
The oxidising agent selected illustrates a common technique of general applicability with the
C6H5CH2OH → C6H5COOH conversion using MnO4− ion under alkaline conditions.
GCE CHEMISTRY Specimen Assessment Materials 92
Apparatus and Reagents
You are provided with safety goggles and with standard preparative organic glassware i.e. a 250 cm3
round bottomed flask with a water condenser to be used under reflux, two 250 cm3 beakers and a
Büchner flask and funnel. You will also be provided with a sample of phenylmethanol and materials
for the preparation of the oxidising mixture will be available. The reagents needed for the tests will
also be to hand.
Safety Considerations
As well as noting the general safety instructions it should be remembered that the solution used in the
preparation is quite strongly oxidising. It is important therefore that, if this is splashed on the skin, it
should be washed off as soon as possible.
Phenylmethanol (benzyl alcohol)
The main hazard is by inhalation or swallowing. Gloves and goggles must be worn when measuring
out the liquid. Phenylmethanol irritates the eyes. In the event of eye or skin contact wash with plenty
of water or saline solution and seek medical advice.
Concentrated sulfuric and hydrochloric acids
Gloves and goggles must be worn.
‘Bumping’ of the Mixture
In order to minimise the chance of ‘bumping’ during the initial reflux of the reagents (due most
probably to the separation of manganese(IV) oxide as the reaction proceeds) the following points are
suggested:
Steady heating should be applied so that the mixture refluxes smoothly and gently. Avoid great
changes in the rate of heating, and especially do not allow the mixture to come off the boil since in
the circumstances reheating is more likely to result in ‘bumping’.
If desired the scale of the preparation may be reduced (say to one half). A smaller volume of
reactants in the 250 cm3 flask is more likely to reflux gently and to stay off the ceiling!
Procedure
Boil phenylmethanol (2⋅09 g, equivalent to 2 cm3, density 1⋅045 g cm-3) for 15 minutes under reflux
with 90 cm3 of saturated potassium manganate(VII) solution containing 2⋅0 g of sodium carbonate.
(This leads to the formation of the sodium salt of benzenecarboxylic acid and the precipitation of
brown manganese(IV) oxide.) After cooling somewhat, remove the condenser and clamp the flask in
a fume cupboard. Carefully acidify the mixture by cautiously adding concentrated sulfuric acid in
small quantities, accompanied by similar amounts of 25 % w/w sodium sulfite (Na2SO3) solution,
swirling or stirring the resulting mixture meanwhile. The flask becomes very hot due to the
exothermic nature of the reactions involved. As necessary repeat the addition of concentrated
sulfuric acid and sodium sulfite until the brown precipitate of manganese dioxide (MnO2) has
dissolved.
At this stage patience is called for: the reaction of the brown precipitate of MnO2 with the acidified
sodium sulfite may take a few minutes to get under way and for the precipitate of MnO2 to begin to
clear. The mixture eventually clears to a colourless solution, which, because of the heat generated,
contains the benzenecarboxylic acid in solution. Do not be in too great a hurry to add further acid and
sodium sulfite: this is because if the final volume of solution is too great it may later be difficult to get
the dissolved benzenecarboxylic acid to crystallise. (Should the mixture fail to clear, check first that
it is actually acidic. If so, bring the contents of the flask gently to the boil and filter hot.)
Now transfer the mixture to a beaker, cool in ice and allow the benzenecarboxylic acid to crystallise.
(If crystallisation is slow to occur it may be assisted by gently scratching the inside surface of the
beaker with a glass rod.)
GCE CHEMISTRY Specimen Assessment Materials 93
Remove the precipitated white solid, benzenecarboxylic acid, by filtration, using a Büchner funnel.
Then wash the solid with a small amount (about 10 cm3) of ice cold water and recrystallise from
water, using the minimum volume required to ensure that dissolving in the hot solvent (about 90 ºC)
is complete. Dry the resulting product, initially between filter papers and then in an oven at 50 ºC.
Record the yield (in g) and the melting temperature.
Tests on Benzenecarboxylic Acid
Carry out the following tests on your product noting the resulting observations and any conclusions
made.
1.
Test the solubility in sodium hydroxide solution.
2.
Test for any reaction with sodium hydrogencarbonate solution.
3
Heat about 0⋅5 g of the solid with 1 cm3 of ethanol and a few drops of concentrated sulfuric
acid. Cool and pour (carefully) into a few cm3 of water in a test tube and note any
characteristic odour.
4.
React with neutral iron(III) chloride solution.
Analysis, Evaluation and Questions
Record your results and calculations on the proforma and answer the questions in the proforma.
Allocation of Marks
The 30 marks available for this experiment are allocated as follows:
Planning [5]; Implementing [15]; Analysing [5]; Evaluating [5]
GCE CHEMISTRY Specimen Assessment Materials 94
Centre Name ………………………………………………Centre Number ……………………
Candidate’s Name …………………………………………Candidate’s Number ………………
Proforma for Unit 6 O1
A study of the oxidation reactions of primary alcohols
(Attach further sheet(s), in the appropriate position, if you need more space)
Plan
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
[2]
Results
Preparation of benzenecarboxylic acid, C6H5COOH
Mass of phenylmethanol used
=
..............................g
Mass of recrystallised product
=
..............................g
Melting temperature of recrystallised product
=
.............................. ºC
[6]
Yield
=
............................... %
[5]
Calculation of % yield
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
[1]
GCE CHEMISTRY Specimen Assessment Materials 95
Tests on C6H5COOH
Test 1:
The solubility in sodium hydroxide
Observation ................................................................................................................
..................................................................................................................................................
[1]
Inference ...................................................................................................................
..................................................................................................................................................
Test 2:
[1]
Reaction with sodium hydrogencarbonate solution
Observation .............................................................................................................................................
..................................................................................................................................................
[1]
Inference .................................................................................................................................................
..................................................................................................................................................
Test 3:
[1]
Reaction with ethanol and conc. sulfuric acid
Observation .............................................................................................................................................
..................................................................................................................................................
[1]
Inference .................................................................................................................................................
..................................................................................................................................................
[1]
GCE CHEMISTRY Specimen Assessment Materials 96
Test 4:
Iron(III) chloride solution often contains a large excess of HCl. Prepare a few cm3 of a neutral
solution as follows. Add to the FeCl3 solution dilute sodium hydroxide solution drop by drop until a
small but permanent precipitate of iron(III) hydroxide is obtained. Filter this off using fluted filter
paper and collect the filtrate in a boiling tube. (Solution A)
Place about 0⋅5 g of benzenecarboxylic acid in another boiling tube and add a slight excess of
aqueous ammonia until the solution is just alkaline to litmus paper. Add a boiling granule and boil
until the vapours evolved no longer discolour moist red litmus. (Solution B)
(i)
To Solution B add a few drops of the neutral iron(III) chloride solution. (solution A)
(ii)
To the solution from (i) above add dilute sulfuric acid until just in excess.
Observation(s) ..........................................................................................................................................
...................................................................................................................................................................
..................................................................................................................................................
[1]
Inference(s) ...............................................................................................................................................
...................................................................................................................................................................
..................................................................................................................................................
[1]
GCE CHEMISTRY Specimen Assessment Materials 97
Questions
1.
(a)
The oxidation
C6H5CH2OH
C6H5COOH
is accompanied by a marked colour change as the purple tint due to MnO4– is
discharged. Give the initial and final oxidation state (number) of Mn in the reaction.
Initial Oxidation State ............. Final Oxidation State ..........
(b)
[1]
The oxidation of primary alcohols by ions in alkaline solution may be represented by
the two ion-electron half-equations
RCH2OH + 4OH–
4e
and MnO4– + 2H2O + 3e
RCOOH + 3H2O
MnO2 + 4OH–
Combine these two equations to deduce an overall stoichiometric equation for this
reaction.
[1]
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
2.
In the procedure the brown precipitate of manganese dioxide is removed by treatment with
sodium sulfite, Na2SO3. This is a redox process. Give the oxidation state (number) changes
which are undergone in this reaction by Mn and by S.
[1]
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
3.
Calculate the percentage atom economy for your reaction using the simplified equation
C6H5CH2OH + MnO4−
C6H5COOH + MnO2 + H2O
[1]
[Ar Mn = 55; O = 16; C = 12; H = 1]
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
GCE CHEMISTRY Specimen Assessment Materials 98
4.
Calculate the % atom economy for an alternative method of forming the acid as in the
equation below and state and explain which method is to be preferred.
C6H5CH3 + 1 12 O2 + cobalt catalyst
C6H5COOH + H2O
[2]
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
5.
Evaluate factors in your synthesis, such as the completeness of oxidation of the alcohol and
the crystallisation and recrystallisation stages that may affect your final yield of product.
Consider also the factors that may affect your value for the melting temperature.
[2]
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
…..................……………………………………………………………………………………
GCE CHEMISTRY Specimen Assessment Materials 99
ASSESSMENT UNIT 6 O1
TEACHER RESULTS SHEET
200 . . .
Centre Name: ……………………………………..… Centre Number: …………………
This form should be completed, as appropriate, by the subject teacher and accompany
the work of the candidate(s) sent for assessment.
Experiment O1
A study of the oxidation reactions of primary alcohols
Preparation of C6H5COOH
Yield of recrystallised product
.............................. %
Melting temperature of recrystallised product
.............................. ºC
Signed:......................................................................... Date:...............................................
(Subject Teacher)
GCE CHEMISTRY Specimen Assessment Materials 100
Experiment O1 - Technical Advice Notes for Teachers and Technicians
A study of the oxidation reactions of primary alcohols
The apparatus and reagents required are listed below.
Universally available items may not be included.
Each student will require
•
•
•
•
•
•
•
safety goggles
250 cm3 round bottomed flask (A)
water condenser
test tubes or boiling tubes
access to melting temperature apparatus (or equivalent)
Büchner flask and funnel plus water pump
two 250 cm3 beakers
Preparation
phenylmethanol (benzyl alcohol)
saturated solution of potassium manganate(VII) containing 2⋅0 g of sodium carbonate per 100 cm3
concentrated sulfuric acid
25 % w/w sodium sulfite (Na2SO3) solution
sodium hydroxide solution
sodium hydrogencarbonate solution
ethanol
Further Technical Advice Notes for Teachers and Technicians
A saturated solution of potassium manganate(VII) contains 6⋅4 g of KMnO4 per 100 g of water at 20
ºC .
The solubility of sodium sulfite, Na2SO3, is about 25 g per 100 g of water at 15 ºC.
Acidification of the reaction mixture with H2SO4 is required initially to destroy any Na2CO3 present
and thereafter, with the added Na2SO3, to reduce any unreacted KMnO4 and the precipitated MnO2 to
Mn2+, as well as liberating C6H5COOH from its sodium salt.
It is likely that the reaction of MnO2 with SO32– / H+ is an autocatalytic process, facilitated by the
Mn2+ produced in the reaction - hence the induction period often observed.
The solubility of benzenecarboxylic acid in water is about 0⋅21 g per 100 g at 17⋅5 ºC and 2⋅2 g per
100 g at 75 ºC, so that the temperature coefficient of the solubility is comfortably sufficient for
recrystallisation from this solvent. Solutions of this compound can, however, easily supersaturate and
be reluctant to crystallise - hence the desirability of using concentrated reagents (H2SO4 and Na2SO3)
so as to minimise the total volume of the reaction mixture.
The use of conc. H2SO4 instead of conc. HCl is reported to be superior and also obviates the
possibility of chlorine being liberated on reaction with any excess KMnO4.
It has been reported that during the initial reflux of the reagents some students encountered violent
‘bumping’ of the mixture. This is most probably due to the separation of insoluble manganese(IV)
oxide as the reaction proceeds. In order to minimise the chances of this occurrence the following
points are suggested:
GCE CHEMISTRY Specimen Assessment Materials 101
Steady heating should be applied so that the mixture refluxes smoothly and gently. Avoid great
changes in the rate of heating, and especially do not allow the mixture to come off the boil since in
such circumstances reheating is more likely to result in ‘bumping’.
If desired the scale of the preparation may be reduced (say to one half). A smaller volume of reactants
in the 250 cm3 flask is more likely to reflux gently and to stay off the ceiling!
The reaction is more likely to proceed smoothly (without ‘bumping’) if either mechanical stirring or
isomantle heating (or both) are available.
GCE CHEMISTRY Specimen Assessment Materials 102
UNIT 6 Experiment I2 – Candidate Instruction Sheet
Analytical Crossword Puzzle - Identification of six inorganic salts by the way in which they
react with each other
Introduction
This exercise is designed to enhance your understanding of the behaviour of inorganic salts in
solution, especially as regards precipitation reactions and has a major planning component.
You will be provided with six solutions, labelled A - F. These will contain six different inorganic
salts, as listed below. You will not, however, know which salt is contained in which solution. Your
task is first to devise and then to implement a plan whereby you can determine unambiguously which
salt is contained in which solution: for this purpose you may use only the way in which these six
solutions react with each other. No other tests are permitted, although you may use water whenever
you wish. The six inorganic salts are as follows:
barium nitrate
lead nitrate
magnesium sulfate
potassium iodide
sodium carbonate
zinc nitrate
The concentrations of all the solutions lie in the range 0⋅10 - 0⋅20 mol dm-3.
Aim
(a)
Gather information on the behaviour of the given solutions, especially with regard to
precipitation reactions.
(b)
Devise a plan that will enable you to identify the salts.
(c)
Carry out the planned experiments on a test tube scale.
(d)
Evaluate your results and identify the solutions.
(e)
Answer the associated questions in the proforma.
Apparatus and Reagents
You are provided with safety goggles, dropping pipettes and a plentiful supply of test tubes.
Safety Considerations
As well as noting the general safety instructions it should be noted that all solutions of barium and
lead salts are markedly toxic and should be handled appropriately.
GCE CHEMISTRY Specimen Assessment Materials 103
Procedure
You should first consider the effect of adding a small sample of any one solution to separate samples
of all the others and the observable effects which would then occur.
You should then indicate how many of the solutions could be unambiguously identified in this way,
stating clearly the basis of your approach and explaining fully the chemistry involved. Present your
plan in as concise and logical a fashion as possible: you may use a grid (or other diagrammatic
approach) or extended prose or both, as you please. Your scheme will be assessed on the extent to
which it would actually work, on the number of compounds which could be fully identified and on its
efficiency.
Your plan should be shown to your supervisor before it is implemented.
You are advised that the iodide, nitrate and sulfate of zinc are all readily soluble in water. However,
for the carbonates, only those of Group 1 metals are similarly soluble.
The tests described in your scheme should now be carried out. Take care to rinse your dropping
pipettes thoroughly with water between tests so as to avoid contamination of your supplied solutions.
It should not be necessary to use more than a few cm3 of solution for each test.
Analysis and Evaluation of results and Questions
Describe your observations clearly and fully in each case. If no apparent reaction occurs this fact
must be stated – a dash or a blank is not sufficient. A three column system of Test, Observation and
Conclusion is provided in the accompanying proforma: you may use this or a grid or extended prose
or any combination of these, as you please. State clearly the identities of the six samples, A – F, with
which you have been supplied and explain how these conclusions have been reached.
Answer the questions in the proforma.
Credit will be given for:
your plan
the correct identification of the six compounds, A – F,
the clear reporting of the tests, especially the observations,
correctly drawn conclusions and inferences,
recognising and explaining the nature of any reactions occurring in solution.
Allocation of marks
The 30 marks available for this experiment are allocated as follows:
Planning [9]; Implementing [6]; Analysing [12]; Evaluation [3]
GCE CHEMISTRY Specimen Assessment Materials 104
ASSESSMENT UNIT 6 I2 SUMMER 200…..
Centre Name ………………………………………………Centre Number ……………………
Candidate’s Name …………………………………………Candidate’s Number ………………
Proforma for Expt. I2
Identification of six inorganic salts by the way in which they react with each other
(Attach further sheet(s), at the appropriate position, if you need more space)
Plan
Describe below as concisely as possible your scheme of attack to the problem. You should
particularly make clear the expected observations (or absence of them) for the various interactions and
how you would use these to draw your conclusions.
You may use either extended prose or a reaction grid (or similar diagram) or both, as you wish.
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GCE CHEMISTRY Specimen Assessment Materials 105
Question
1.
Write full ionic equations for three of the reactions proposed in your plan.
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[3]
GCE CHEMISTRY Specimen Assessment Materials 106
Results
Test
Observation(s)
Conclusion(s)
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GCE CHEMISTRY Specimen Assessment Materials 107
Analysis
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Evaluation
Questions
2.
Discuss the possible effect of using very different solution concentrations on your results.
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[1]
GCE CHEMISTRY Specimen Assessment Materials 108
3.
Relate the solubilities of the products of the reactions to the position of the metal in the
Periodic Table.
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[2]
GCE CHEMISTRY Specimen Assessment Materials 109
ASSESSMENT UNIT 6 I2
TEACHER SAMPLE ALLOCATION SHEET
200 . . .
Centre Name: ……………………………………..… Centre Number: …………………
This form should be completed, as appropriate, by the subject teacher and accompany
the work of the candidate(s) sent for assessment.
Experiment I2
Identification of six inorganic salts by the way in which they react with each other
Indicate the letter A - F assigned to the six solutions as listed below:
Letter ( A – F)
(1)
barium nitrate, Ba(NO3)2
.............................
(2)
lead nitrate, Pb(NO3)2
.............................
(3)
magnesium sulfate, MgSO4
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(4)
potassium iodide, KI
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(5)
sodium carbonate, Na2CO3
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(6)
zinc nitrate, Zn(NO3)2
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Signed: ...................................................
(Subject Teacher)
Date:
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GCE CHEMISTRY Specimen Assessment Materials 110
Experiment I2 – Technical Advice Notes for Teachers and Technicians
Identification of six inorganic salts by the way in which they react with each other
The apparatus and reagents required are listed below.
Universally available items may not be included.
Each student will require:
•
•
•
safety goggles
two dropping pipettes
a plentiful supply of test tubes
Each student will also require six sample solutions, randomly labelled A – F, allocated by the
supervisor, these to be of concentration within the range 0⋅10 - 0⋅20 mol dm-3.
(1)
(2)
(3)
(4)
(5)
(6)
barium nitrate, Ba(NO3)2
lead nitrate, Pb(NO3)2
magnesium sulfate, MgSO4
potassium iodide, KI
sodium carbonate, Na2CO3
zinc nitrate, Zn(NO3)2
GCE CHEMISTRY Specimen Assessment Materials 111
UNIT 6 Experiment O2 – Candidate Instruction Sheet
Chemical Detection - the identification of six organic compounds by reactions with designated
reagents
Introduction
This exercise is designed to enhance your understanding of functional group behaviour and to
strengthen the linkage between theory and experiment. You are required to devise a plan to identify
six different organic compounds, labelled A – F, where these are drawn from the following list of
eight compounds:
l-aminobutane
CH3CH2CH2CH2NH2
benzenecarbaldehyde (benzaldehyde)
C6H5CHO
benzenecarboxylic acid (benzoic acid)
C6H5COOH
butanone
CH3COCH2CH3
diphenylmethanone (benzophenone)
C6H5COC6H5
ethanamide
CH3CONH2
ethylbenzenecarboxylate
C6H5COOC2H5
benzenecarbonitrile (benzonitrile)
C6H5CN
Only a limited range of reagents is permitted for this purpose (given below). You are, however,
allowed to use methanol as a solvent for any solids insoluble in water.
You are then required to implement your plan to identify all the six samples, recording and
interpreting all relevant observations. You should briefly justify all your conclusions.
You may use the fact that a given sample is a solid or a liquid as supporting evidence, but the
determination of the melting or boiling temperature of any of the supplied samples (or of their
derivatives) is not allowed. Your plan of attack should be based on the chemical properties of the
compounds and not on physical properties, such as their division into solids and liquids, or on
characteristic odours.
Aim
(a)
Research relevant information on the behaviour of the functional groups in the given
compounds.
(b)
Devise a plan that will enable you to identify the compounds.
(c)
Implement your plan.
(d)
Analyse and evaluate your results and thus identify the compounds.
(e)
Answer the associated questions in the proforma.
GCE CHEMISTRY Specimen Assessment Materials 112
Apparatus and Reagents
You are provided with safety goggles and with a plentiful supply of test tubes, boiling tubes and small
beakers. Apart from water, only the following limited range of reagents will be available:
dilute sodium hydroxide solution (concentration about 2 mol dm-3);
dilute sulfuric acid, (concentration about 1 mol dm-3);
sodium hydrogencarbonate (solid);
test papers (i.e. red and blue litmus or similar indicator papers);
2,4-dinitrophenylhydrazine reagent;
materials for preparing Tollens' reagent;
materials for preparing the reagent for the iodoform test.
sodium nitrite (sodium nitrate(III))
Safety Considerations
As well as observing the general safety instructions the following points should be noted.
1-aminobutane
This causes burns and is harmful by inhalation, skin contact and if swallowed. The liquid is irritating
to eyes and the respiratory system. Eye protection should be worn and the liquid should be dispensed
in a fume cupboard.
Benzenecarbaldehyde (benzaldehyde)
This causes eye irritation and eye protection should be used. The liquid is combustible with a flash
point of 64 oC
Benzenecarboxylic acid (benzoic acid)
No major risk.
Butanone
Eye protection should be worn. The liquid is a fire hazard.
Diphenylmethanone (benzophenone)
This causes skin and eye irritation. Eye protection should be worn.
Ethanamide
Category 3 carcinogen. Eye protection should be worn.
Ethylbenzenecarboxylate
Eye protection should be worn.
Benzenecarbonitrile (benzonitrile)
Harmful in contact with skin and if swallowed. Irritating to skin and eyes Eye protection should be
worn.
Note also that gloves should be worn for both the solution of the 2,4-dinitrophenylhydrazine reagent
and the solution required for the iodoform test as these may badly stain the skin if spilt on it. In such
eventualities the solution should be washed off as soon as possible. In addition Tollens' reagent
should not be made up until needed and any surplus then disposed of: this is because on standing, the
reagent may deposit an unstable residue which could decompose violently.
GCE CHEMISTRY Specimen Assessment Materials 113
Procedure
You are required first to plan a sequence of tests which would enable all of the eight listed
compounds to be identified without ambiguity. (You will later be given six of these, chosen at the
discretion of your supervisor, for actual identification.) You should try to avoid an approach which
merely advocates 'test everything with everything', but seek to use primarily tests which will give
clear results with several compounds (enabling those compounds to be distinguished from the others)
or at least allow a number of possibilities to be discounted.
Wherever confirmatory tests are available these should also be carried out and the results recorded.
You will be assessed on the extent to which your plan would actually work and also on its efficiency
(i.e. the avoidance of any tests not actually necessary). It is emphasised that for any particular test to
be useful it must lead to some observable outcome. The mere recitation of the chemistry involved
without a description of the expected observations that would occur will not be sufficient.
Your plan should now be shown to your supervisor before it is implemented.
You will be then be provided with six samples, labelled A – F, on which the tests in your plan should
be carried out.
Results, Analysis, Evaluation, Conclusions and Questions
The tests in your plan should, in each case, be fully described, as should their outcomes (i.e.
observations, even if no apparent reaction occurs) together with any conclusions drawn.
(A three column system of Test, Observation and Conclusion is provided in the accompanying
proforma).
Although your plan may establish the identities of your samples in a relatively small number of tests,
you should wherever appropriate, use suitable confirmatory tests to back up your conclusions.
Remember that your task is not finished when you have identified all your samples. Wherever you
can you should interpret all your observations.
Credit will be given for:
the correct identification of the six compounds, A – F,
the clear reporting of the tests, especially the observations,
correctly drawn conclusions and inferences,
a brief evaluation of the use and limitations of the method and reagents employed,
correctly answering the questions in the proforma.
As well as completing the proforma you may, if you wish, also use extended prose to summarise what
you have done and to clarify how you have reached your conclusions.
Allocation of marks
The 30 marks available for this experiment are allocated as follows:
Planning [9]; Implementing [6]; Analysing [12]; Evaluation [3]
GCE CHEMISTRY Specimen Assessment Materials 114
ASSESSMENT UNIT 6 O2 SUMMER 200…..
Centre Name ………………………………………………Centre Number ……………………
Candidate’s Name …………………………………………Candidate’s Number ………………
Proforma for Expt. O2
Identification of six organic compounds by reactions with designated reagents
(Attach further sheet(s), in the appropriate position, if you need more space)
Plan
Describe as concisely as possible your scheme of attack to the problem. You should make clear
the tests which you would apply,
the sequence in which you would apply them,
the expected observations (or absence of them), and
how you would reach your conclusions.
Any inferences made from the physical state (i.e. solid or liquid) of the compounds should also be
mentioned here (as well as in the actual application of the scheme later).
You may use either extended prose or a diagrammatic flow chart approach (or both), as you wish.
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GCE CHEMISTRY Specimen Assessment Materials 115
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GCE CHEMISTRY Specimen Assessment Materials 116
Results
Test
Observation(s)
Conclusion(s)
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GCE CHEMISTRY Specimen Assessment Materials 117
Analysis and Evaluation
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GCE CHEMISTRY Specimen Assessment Materials 118
Questions
1.
State how the presence of a carbonyl group in one of your compounds may be detected.
[1]
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2.
State how aldehydes and ketones may be distinguished from one another.
[1]
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3.
State for which compounds a simple test of acidity or basicity would be useful.
[1]
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4.
Explain why to rely purely on physical properties of the compounds is unsatisfactory.
[1]
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5.
Despite question 4, explain why the different solubilities of two carboxylic acids in water
allows you to distinguish between two of the compounds on the list.
[2]
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GCE CHEMISTRY Specimen Assessment Materials 119
ASSESSMENT UNIT 6 O2
TEACHER SAMPLE ALLOCATION SHEET
200...
Centre Name …………………………………..……
Centre Number ……………
This form should be completed, as appropriate, by the subject teacher and accompany
the work of the candidate(s) sent for assessment.
Experiment O2
Identification of six organic compounds by reactions with designated reagents
† Each candidate should be given samples of six of the eight compounds listed on the Technical
advice note page for Teachers and Technicians. These samples should differ (as far as possible)
from candidate to candidate. Indicate on the form the numbers, using the sequence, on the Technical
advice note page.
Candidate
Examination
Number
Name
e.g. XXXXXXXX
XXXXXX
XXXXXXXXXX
† Sample Allocated
Nos. (1) – (8)
(as on page 103)
A (2);
B(3);
C(4);
D(5); E(6);
F(7)
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Signed: .........................................................................
(Subject Teacher)
Date: ...............................................
GCE CHEMISTRY Specimen Assessment Materials 120
Answers to questions:
1.
Formation of an orange ppt. with 2,4-dinitrophenylhydrazine (1)
AO1
2.
Aldehydes give silver mirror with Tollens' reagent / red pt with Fehling's reagent. (1)
AO1
3.
1-aminobutane is basic and benzenecarboxylic acid is acidic (1)
AO1
Implementing [6]
Actual test results and observations (6)
Analysing [12]
Inferences from tests (6) (1 for each cpd)
Correct identity of cpds (6) (1 for each cpd)
Evaluation [3]
Answers to questions:
4.
These are often not sufficiently specific to identify compounds (1)
AO2
5.
Ethanamide, when hydrolysed by heating with NaOH(aq) and then acidifying, forms a
solution of soluble ethanoic acid. (1)
AO2
Benzonitrile, when similarly treated, gives a white ppt. of insoluble benzenecarboxylic acid.
(1)
AO2
Maximum Mark [30]
GCE CHEMISTRY Specimen Assessment Materials 121
Experiment O2 – Technical Advice Notes for Teachers and Technicians
Identification of six organic compounds by reactions with designated reagents
•
The apparatus and reagents required are listed below.
Universally available items may not be included.
Each student will require:
•
•
•
•
•
•
•
•
•
•
•
*
safety goggles
test tubes and boiling tubes
small beakers
dilute sodium hydroxide (ca. 2 mol dm-3)
dilute sulfuric acid (ca. 1 mol dm-3)
sodium hydrogencarbonate (solid)
test papers (i.e. red and blue litmus or similar indicator papers)
2, 4-dinitrophenylhydrazine reagent
sodium nitrite (sodium nitrate(III))
materials for preparing Tollens' reagent*
materials for preparing the reagent for the iodoform test †
Tollens' reagent requires ca. 0⋅1 mol dm-3 silver nitrate solution and ca. 2 mol dm-3 aqueous
ammonia.
†The iodoform reagent requires iodine in potassium iodide solution and sodium hydroxide
solution
Each student will also require six samples, as allocated by the supervisor, from the following list.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
l-aminobutane
benzenecarbaldehyde (benzaldehyde)
benzenecarboxylic acid (benzoic acid)
butanone
diphenylmethanone (benzophenone)
ethanamide
ethylbenzenecarboxylate
benzenecarbonitrile (benzonitrile)
CH3CH2CH2CH2NH2
C6H5CHO
C6H5COOH
CH3COCH2CH3
C6H5COC6H5
CH3CONH2
C6H5COOC2H5
C6H5CN
GCE CHEMISTRY Specimen Assessment Materials 122
MARK SCHEME
SPECIMEN PAPER
CH1
Range of acceptable answers.
The answers given in the marking schemes in this Specimen Assessment Materials document are
suggestions that would be acceptable to the Chief Examiner. However, alternative answers that are
correct and relevant to the question are to be given appropriate credit by markers.
Assessment of Quality of Written Communication (QWC) in AS/A Chemistry
Answers to questions, whether in one sentence or in a paragraph, will be assessed as to whether
the candidate has communicated the appropriate chemistry clearly and unambiguously.
Candidates will need to
(i)
(ii)
(iii)
ensure that text is legible and that spelling, punctuation and grammar are accurate so
that meaning is clear;
select and use a form and style of writing appropriate to purpose and to complex
subject matter;
organise information clearly and coherently, using specialist vocabulary when
appropriate.
The inclusion of (QWC) in the marking schemes indicates to markers where the quality of a
candidate’s written communication will be awarded marks.
GCE CHEMISTRY Specimen Assessment Materials 123
SECTION A
1.
Particle
proton
neutron
electron
Relative Charge
+1
no charge
-1
Relative Mass
1
1
1/1840
[1]
2.
(a)
(i)
Ge
[1]
(ii)
C and Ge
[1]
(b)
3s
↑↓
3p
↑↓ ↑↓ ↑↓
↑
↑
3d
↑ ↑
↑
4s
↑
[1]
3.
A
[1]
4.
D
[1]
5.
15.9 years
[1]
6.
A
[1]
7.
(i)
35 and 37
[1]
(ii)
75% and 25%
[1]
Total [10]
GCE CHEMISTRY Specimen Assessment Materials 124
SECTION B
8.
(a)
(i)
The catalyst is in a different physical state to the reactants.
[1]
(ii)
No change.
[1]
(iii)
uncatalysed
energy
catalysed
exothermic reaction
[1]
[1]
[1]
reaction path / extent of reaction
(b)
Reactions occur when collisions between reacting particles possess necessary
activation energy.
[1]
When temperature is increased the kinetic energy of the molecules increase.
[1]
The fraction of collisions possessing the activation energy increases.
[1]
Therefore there are a greater number of successful collisions (per unit time) that lead
to a reaction.
[1]
(QWC)
• legible text and accurate spelling, punctuation and grammar so that meaning is
clear (1)
• a coherent and clearly expressed response using a style appropriate to complex
subject matter (1)
[2]
GCE CHEMISTRY Specimen Assessment Materials 125
(c)
(i)
ΔHf products – ΔHf reactants = –46 kJ mol-1
[1]
ΔHf ethanol = –46 + (–242 + 52.3)
[1]
-1
(ii)
ΔHf ethanol = –235.7 kJ mol
[1]
ΔH reaction = –235.7 + 284 = 48.3 kJ mol-1
(Mark consequentially to (c)(i))
[1]
Total [15]
9.
(a)
(b)
(i)
To prevent heat losses to the surroundings.
(ii)
To find out how much heat was liberated in raising the temperature of the
water. / Needed in the ΔH equation.
[1]
(iii)
To give good heat conduction to the water. / Heating the metal uses little
heat.
[1]
(iv)
To find the amount/number of moles used.
(v)
Moles ethanol =
(vi)
ΔH =
1.5
= 0.0325
46.1
500 × 4.18 × 19.5
= 1254000 J
0.0325
[1]
[1]
[1]
[1]
ΔH = –1254 kJ mol-1
[1]
(vii)
Some heat will be lost to the surroundings.
[1]
(i)
Suitable axes and scale
[1]
Rate on y-axis
[1]
All points correct
(1 error 1 mark, >1 error 0 marks)
[2]
Correct line of best fit
[1]
(ii)
Temperature
[1]
(iii)
Measure volume of oxygen (with syringe)
[1]
Total [15]
GCE CHEMISTRY Specimen Assessment Materials 126
10.
(a)
(i)
Effective
nuclear charge is increasing.
[1]
[1]
(Accept increasing nuclear charge
outweighs shielding effect of electrons present)
(ii)
For boron, the p electron is further from the nucleus
and is more effectively shielded.
[1]
[1]
(iii)
Sodium has one more inner shell than lithium
Greater shielding for sodium.
[1]
[1]
(iv)
4560 kJ mol-1
[1]
(b)
Energy levels are quantised.
[1]
Only certain energy transitions are possible and only certain frequencies are observed.
[1]
(QWC)
• information organised clearly and coherently, using specialist vocabulary when
appropriate (1)
[1]
(c)
(i)
Negative plates.
Accelerate the ions to high speed.
[1]
[1]
(ii)
Deflects the ions to a detector.
[1]
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 127
11.
(a)
(i)
Temperature
T/K
600
650
700
750
800
850
900
(ii)
[1]
Relative rate of the
forward reaction
logkrel
10.16
10.90
11.59
12.14
12.66
13.11
13.50
Fractional conversion to C
at equilibrium
f
0.997
0.988
0.967
0.930
0.875
0.798
0.708
Product of
logkrel x f
10.13
10.77
11.21
11.29
11.08
10.46
9.56
I
All points correct
Correct line of best fit
[1]
[1]
II
All points correct
Correct line of best fit
[1]
[1]
III All points correct
Correct line of best fit
[1]
[1]
(b)
With increasing temperature, rate of forward reaction increases but percentage
conversion to C at equilibrium decreases.
[1]
Plot 3 shows that 750 K is optimum temperature.
[1]
(c)
Position of equilibrium moves to the right.
More (gas) moles on the left hand side.
[1]
[1]
(d)
Enthalpy change for the equilibrium is negative
because the equilibrium shifts to the left as temperature is increased.
[1]
[1]
Total [13]
12.
(a)
(i)
A
Increased use of coal implies new deposits can be accessed.
[1]
[1]
(ii)
B
Increased use of nuclear energy implies safer to dispose of it.
[1]
[1]
(iii)
C
Increased use of renewable energy implies more wind farms built.
[1]
[1]
OR
D
Less fossil fuels being burned to give required reduction in CO2 emissions.
(b)
Advantage - does not produce CO2 /add to global warming.
Disadvantage - hydrogen is very explosive
[1]
[1]
(c)
(i)
An acid is a proton donor
[1]
(ii)
More fossil fuels burnt in winter
[1]
(iii)
Weathers limestone buildings/pollutes lakes etc.
[1]
GCE CHEMISTRY Specimen Assessment Materials 128
(d)
(i)
n NaOH =
0.0950 × 24.0
1000
= 2.28 × 10 −3
(ii)
n H2SO4 =
[1]
2.28 × 10 −3
= 1.14 × 10 −3
2
conc. H2SO4 =
[1]
1.14 × 10 −3
20.0 × 10 −3
= 5.43 × 10 −2 mol dm-3
[1]
Total [14]
Section B Total [70]
GCE CHEMISTRY Specimen Assessment Materials 129
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
MARK SPECIFICATION GRID
GCE CHEMISTRY
UNIT TEST
Year of Examination (Specimen)
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Page 1 of 2
Session: summer/winter
AS Unit CH1
Assessment Objective
Target Totals
Question
Number
1
Specification
Reference
1.1.a
AO1
AO2
AO3
35
35
10
Paper
Total
Mark
Synoptic
Quality of
written
commun.
80
9
9
Other requirements
1
2a
1.1.c
2
2b
1.1.m
1
3
1.1.f
4
1.1.e
5
1.1.h
1
6
1.2.d
1
7
1.2.b
2
8ai
2.3.h
1
8aii/iii
2.3.g
2
8aiii
2.3.e
2
8b
2.3.d
6
8c
2.2.f
4
9ai-iv
2.2.e
2
9av
1.2.d
1
9b
2.3.b
2
10ai/ii/iii
1.1.j
6
10aiv
1.1.k
10b
1.1.o
1
1
9
5
5
1
9
3
10c
2.1.b
3
11a/b
2.1/2.3
11c
2.1.b
11d
2.1.b
2
12a
3.b
6
12b
3.c
2
9
2
GCE CHEMISTRY Specimen Assessment Materials 130
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
MARK SPECIFICATION GRID
GCE CHEMISTRY
UNIT TEST
Year of Examination (Specimen)
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Page 1 of 2
Session: summer/winter
AS Unit CH1
Assessment Objective
Target Totals
AO1
AO2
AO3
35
35
10
Question
Number
12ci
Specification
Reference
2.1.c
12cii/iii
3.b
2
12d
2.1.e
3
Raw
Totals:
1
34
36
10
Paper
Total
Mark
Synoptic
Quality of
written
commun.
80
9
9
Other requirements
GCE CHEMISTRY Specimen Assessment Materials 131
MARK SCHEME
SPECIMEN PAPER
CH2
Range of acceptable answers.
The answers given in the marking schemes in this Specimen Assessment Materials document are
suggestions that would be acceptable to the Chief Examiner. However, alternative answers that are
correct and relevant to the question are to be given appropriate credit by markers.
Assessment of Quality of Written Communication (QWC) in AS/A Chemistry
Answers to questions, whether in one sentence or in a paragraph, will be assessed as to whether
the candidate has communicated the appropriate chemistry clearly and unambiguously.
Candidates will need to
(i)
(ii)
(iii)
ensure that text is legible and that spelling, punctuation and grammar are accurate so
that meaning is clear;
select and use a form and style of writing appropriate to purpose and to complex
subject matter;
organise information clearly and coherently, using specialist vocabulary when
appropriate.
The inclusion of (QWC) in the marking schemes indicates to markers where the quality of a
candidate’s written communication will be awarded marks.
GCE CHEMISTRY Specimen Assessment Materials 132
SECTION A
1.
I
(i)
δ+
x x
2.
chlorine is more electronegative than iodine (both needed)
x
(i)
Sr2+
+
SO42-
[1]
Butan-2-ol
[1]
CH3
H
C
CH3
Br
(1)
CH3
5.
H
C+
Br
_
(1)
[2]
CH3
Cl
H 3C
C
H
6.
[1]
SrSO 4
White precipitate
4.
[1]
[1]
xx
(ii)
3.
δ−
I Cl
x
x
(ii)
Cl
C
Cl
[1]
(i)
4
[1]
(ii)
Nickel / Ni / platinum / Pt
[1]
Total [10]
GCE CHEMISTRY Specimen Assessment Materials 133
SECTION B
7.
(a)
Boron trifluoride has three bonding pairs and no lone / non-bonding pairs of electrons
(1), giving a trigonal / triangular planar molecule (1).
[3]
The F-B-F angle is 120o. (1)
(b)
(i)
Boron has no available outer electrons for bonding to the oxygen atom /
electron deficient (1)
Oxygen provides a lone pair of electrons for bonding (1)
[2]
(ii)
Four bonding pairs of electrons, no lone pairs (1), ∴ tetrahedral (1)
(c)
(i) MgCO3.CaCO 3 + 2 H2SO 4
correct formulae (1)
[2]
MgSO 4 + CaSO 4 + 2CO 2 + 2H2O
balancing (1)
(ii)
Effervescence (1), white precipitate (1)
(iii)
87 g produced per 100 g of water
(1)
∴ 870 g produced per 1000g / 1 kg of water
∴ 870 x 200 g produced for 200 kg of water
= 174 000 g = 174 kg (1)
[2]
[2]
[2]
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 134
8.
(a)
(b)
(i)
To provide the energy to break the Cl - Cl bond
(ii)
Cl2
(iii)
e.g. Cl
+
+
CH 2COOH
ClCH2COOH
[1]
[1]
Reagent(s) (excess) dilute nitric acid and aqueous silver nitrate (both needed) (1)
Observation
(c)
ClCH2COOH + HCl
CH3COOH
[1]
white precipitate
(1)
[2]
(i)
It cannot exist as E-Z isomers as at one end of the double bond both atoms
are the same.
[1]
(ii)
I
Electrophilic (1), addition (1)
II
Carbocation A is a secondary carbocation and carbocation B is a
primary carbocation (1) secondary carbocations are more stable /
easier to form than primary carbocations, ∴ carbocation A is
preferred and reacts to give 4-chloropentanoic acid. (1)
[2]
[2]
(d)
Destruction of ozone is caused by initial bond fission of the weaker C-Cl bond (1),
the C-F bonds in 1,1,1-trifluoroethane are too strong to be broken in this way. (1)
[2]
(e)
1,1,1- trifluoroethane has only weaker van der Waals forces between molecules,
whereas 2,2,2-trifluoroethanol has, in addition, hydrogen bonding between molecules
(1)
CH2
F3 C
H
O
O
H
CF3
CH2
(1) for showing attraction between oxygen and hydrogen
(1) for partial charges, δ− on oxygen and δ+ on hydrogen
[3]
(QWC)
• information organised clearly and coherently, using specialist vocabulary when
appropriate (1)
[1]
Total [17]
GCE CHEMISTRY Specimen Assessment Materials 135
9.
(a)
Decane is cracked (1) at a high temperature / pressure (1) to produce eg. octane (1)
and ethene.
In the second stage ethene and steam (1) are reacted together at 300 oC / moderate
temperatures (1) and at increased pressures / 60 to 70 atmospheres (1) in the presence
of a phosphoric acid catalyst (1). (any five)
C2H 4 + H 2O
C2H5OH
(1)
[6]
(QWC)
• legible text and accurate spelling, punctuation and grammar so that meaning is
clear (1)
• a coherent and clearly expressed response using a style appropriate to complex
subject matter (1)
[2]
(b)
(i)
e.g. increase the time of fermentation (1) → may increase the yield after a
suitable period of time. (1)
use a different micro-organism (1) → may alter the proportion of products.
(1)
[4]
(ii)
I
propanone gives a peak due to C=O at around 1750 cm-1 (1) the two
alcohols do not contain a C=O bond and therefore do not give this
absorption. (1)
[2]
II
Butan-1-ol has a higher boiling temperature than ethanol (1) as its van
der Waals forces between molecules are greater and ∴ more energy is
needed to separate the molecules into the gas phase (1)
[2]
Total [16]
10.
(a)
(b)
(i)
Strong covalent bonds between atoms (1)
Weak van der Waals forces between layers (1)
[2]
(ii)
Hardness : graphite is soft and the planes slip easily over each other (1)
Electrical conductivity : good conductor of electricity, delocalised electrons
carry charges (1)
[2]
(iii)
Pipelines of carbon hexagons, as in graphite (1) capped at the end with
pentagon of carbon atoms, needed for curvature (1)
[2]
e.g., as catalysts / in drug delivery mechanisms / in sunscreens / in dyes
[1]
GCE CHEMISTRY Specimen Assessment Materials 136
(c)
(i)
Ca2+
O2−
correct structure (1)
correct formulae of ions (1)
crystal co-ordination numbers 6:6 (1)
(ii)
(d)
Ca
Al
+2 in CaO → 0 in Ca metal gain of electrons ∴ reduction (1)
0 in Al metal → +3 in Al2O3 lost of electrons ∴ oxidation (1)
Effervescence / calcium ‘dissolves’ / cloudy solution
indicator turns blue or purple / gives pH >7 (1)
(1) (1)
[3]
[2]
Any two
[3]
Total [15]
11.
(a)
(i)
Gain of an electron gives a full shell which is stable
(ii)
Observation : the (colourless) solution turns a red-brown colour (1)
Ionic equation :
(b)
(i)
Cl2 + 2Br
_
Br2 + 2Cl
[1]
_
(1)
[2]
Ar of bromine is 79.9 ∴ X can only contain one bromine atom (1)
‘Ar’ of the remainder is 94.9 – 79.9 = 15 this must represent all the carbon
and hydrogen (1)
∴ X can only contain one carbon atom, since Ar of carbon is 12, the
remainder must be three hydrogen atoms
molecular formula is CH3Br (1)
(ii)
(c)
[3]
Needs to be volatile or gaseous / readily available / not affect the grain /
effective / dense vapour to penetrate the bottom of the pile of grain (1) (1)
Any two
[2]
Infrared spectroscopy shows a (broad) absorption at 3300–3500 cm-1, characteristic of
an O-H bond (1)
Mass spectroscopy shows two molecular ions (of equal intensities ) at m/e 124 and
[2]
126 corresponding to one bromine atom in C2H4(OH)Br (1)
Total [10]
GCE CHEMISTRY Specimen Assessment Materials 137
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
MARK SPECIFICATION GRID
GCE CHEMISTRY
UNIT TEST
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Year of Examination (Specimen)
Page 1 of 2
Session: summer/winter
AS Unit CH2
Assessment Objective
Target Totals
Question
Number
1 (i)
AO1
AO2
AO3
Paper
Total
Mark
35
35
10
80
Specification
Reference
4.1d
1
1 (ii)
4.1a
1
2 (i)/(ii)
6.2b
2
3
7.1a
1
4
7.2a
1
5
7.2g
6 (i)/(ii)
7.2f
2
7 (a)
4.3c
3
7 (b) (i)
4.1a
2
7 (b) (ii)
4.3c
2
7 (c) (i)
6.2b
2
7 (c) (ii)
6.2b
7 (c) (iii)
4.4b
8 (a) (i)
7.2c
1
2
8 (b)
7.1i
1
1
8 (c) (i)
7.1d
1
8 (c) (ii)
7.2e
8 (d)
7.3e
1
1
8 (e)
4.2a/c
2
2
Raw
Totals:
Other requirements
Synoptic
Quality of
written
commun.
9
9
1
1
2
2
4
9
GCE CHEMISTRY Specimen Assessment Materials 138
WELSH JOINT EDUCATION COMMITTEE
General Certificate of Education
MARK SPECIFICATION GRID
GCE CHEMISTRY
UNIT TEST
CYD-BWYLLGOR ADDYSG CYMRU
Tystysgrif Addysg Gyffredinol
Year of Examination (Specimen)
Page 2 of 2
Session: summer/winter
AS Unit
CH2
Assessment Objective
Target Totals
AO1
AO2
AO3
10
35
35
Specification
Reference
7.2b 7.4d
6
2
9 (b) (i)
9a
2
9 (b) (ii) I
8b
9 (b) (ii) II
4.2d
10 (a) (i)
5b
2
10 (a) (ii)
5e
2
10 (a) (iii)
5c
10b
5g
Question
Number
9 (a)
2
2
2
1
5a / 6.2c
3
10 (c) (ii)
6.1d
2
10 (d)
6.2a / c
3
11 (a) (i)
6.2g
1
11 (a) (ii)
6.2h
1
11 (b) (i)
7.1e
11 (b) (ii)
9a
11 (c)
Raw
Totals:
1
3
2
8a / b
2
36
35
80
Other requirements
Synoptic
Quality of
written
commun.
9
9
9
2
10 (c) (i)
Paper
Total
Mark
9
GCE CHEMISTRY Specimen Assessment Materials 139
MARK SCHEME
SPECIMEN PAPER
CH4
Range of acceptable answers.
The answers given in the marking schemes in this Specimen Assessment Materials document are
suggestions that would be acceptable to the Chief Examiner. However, alternative answers that are
correct and relevant to the question are to be given appropriate credit by markers.
Assessment of Quality of Written Communication (QWC) in AS/A Chemistry
Answers to questions, whether in one sentence or in a paragraph, will be assessed as to whether
the candidate has communicated the appropriate chemistry clearly and unambiguously.
Candidates will need to
(i)
(ii)
(iii)
ensure that text is legible and that spelling, punctuation and grammar are accurate so
that meaning is clear;
select and use a form and style of writing appropriate to purpose and to complex
subject matter;
organise information clearly and coherently, using specialist vocabulary when
appropriate.
The inclusion of (QWC) in the marking schemes indicates to markers where the quality of a
candidate’s written communication will be awarded marks.
GCE CHEMISTRY Specimen Assessment Materials 140
SECTION A
1.
(a)
(b)
(i)
I
nucleophilic addition and elimination / condensation
[1]
II
orange precipitate
[1]
III
lower (1) over a range (1)
[2]
(ii)
C6H10O
(i)
I
NaOH / I2 or NaOCl / KI
[1]
II
yellow precipitate
[1]
(ii)
[1]
Reagent(s) used
eg Tollens’ reagent
Observations
with cis-hex-3-enal
with hex-5-en-2-one
(c)
cis-hex-3-en-1ol
cis-hex-3-enal
(d)
carboxylic acid
oxidation
[1]
[1]
silver mirror
no observable change
OH present C=O absent
OH absent C=O present
[1]
[1]
[1]
[1]
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 141
2.
(a)
Cl
+
FeCl3 (1)
Cl2
+
HCl
(1)
[2]
(b)
(c)
(i)
all reactants and products are gaseous / do not have to dispose of (toxic) HCl
gas / all the chlorine is used in making the product
[1]
(ii)
use a separating funnel
[1]
(i)
nearly all the atoms are used in the product
[1]
(ii)
I
The C-Cl bond is polar, susceptible to nucleophilic substitution
[1]
II
Greater C-Cl bond strength / delocalisation of chlorine lone pair into
the ring, not susceptible to nucleophilic attack
[1]
(d)
the δ− oxygen of methoxy group and the δ + hydrogen of water attract each other [1]
(e)
(i)
(ii)
Reagent(s)
bromine water
[1]
Observation
white precipitate, bromine decolourised
[1]
Mr of Dettol
=
Theoretical yield
157
=
[1]
157 × 1000
122
= 1287 g / 1.28(7) kg
[1]
Total [12]
GCE CHEMISTRY Specimen Assessment Materials 142
3.
(a)
(i)
Number of moles of citric acid
=
5.20 × 1000
192
=
Number of moles of sucrose
=
20.6 × 1000
342
= 60.2
Percentage yield
(ii)
(b)
27.1 × 100
60.2
=
=
27.1
45.0
e.g. how long it takes to produce the maximum yield of citric acid
whether the yield is improved
[1]
[1]
[1]
(i)
CH2
+
H3N
C
O
C
-
O
H
[1]
(ii)
NH2
HOOC
CH2
C
COOH
H
[1]
(iii)
One enantiomer rotates the plane of polarised light (1) in one direction and
the other rotates it (equally) in the opposite direction (1).
This is called a racemic mixture (1)
[3]
(c)
e.g. bromine water (1)
hydroxybenzenecarboxylic
benzenecarboxylic acid (1)
(d)
It contains two double C=C bonds with different groups at each end (1).
Each of these can show E – Z isomerism
(e)
gives a white precipitate / decolourised with 4acid, there is no observable reaction with
[2]
[2]
e.g. concentration / intensity of UV radiation / monochromatic frequency / period of
exposure
ANY TWO
[2]
Total [15]
GCE CHEMISTRY Specimen Assessment Materials 143
SECTION B
4.
(a)
(i)
1-chlorobutane (1) is added to a mixture containing benzene and anhydrous
aluminium chloride (1), which acts as a catalyst (1).
The benzene is in excess compared to the 1-chlorobutane (1).
CH2CH2CH2CH3
+
+
CH3CH2CH2CH2Cl
HCl
(1)
[5]
(ii)
2-butylbenzene has weaker (1) van der Waals forces (1) between molecules.
Less energy is ∴ needed to separate molecules of 2-butylbenzene (1)
∴ boiling temperature is lower.
[3]
(iii)
All CH2 protons are equivalent, as are all the CH3 protons. (1)
Similarly all the aromatic protons are in the same environment. (1)
(iv)
H
e.g.
H
H
C
C
OH
Al2O3
or H2SO4
H
H
reactants (1)
(b)
[2]
products (1)
H2C
CH2
+
H2O
catalyst (1)
[3]
Bromoethane is heated under reflux conditions (1) with an aqueous (1) solution of
sodium hydroxide (1).
This is a hydrolysis reaction (1) of a halogenoalkane.
The equation for this reaction is
C2H5Br
+
NaOH
C2H5OH
+
NaBr
(1)
The lower boiling temperature of ethanol enables it to be separated from the reaction
mixture by fractional distillation (1). (any four)
[4]
e.g. The ethene route is preferred as the ethene is produced directly from the cracking
of crude oil fractions / there are no co-products with this method.
[1]
(QWC)
• legible text and accurate spelling, punctuation and grammar so that meaning is
clear (1)
• a coherent and clearly expressed response using a style appropriate to complex
subject matter (1)
[2]
Total [20]
GCE CHEMISTRY Specimen Assessment Materials 144
5.
(a)
Benzene has a stable delocalised π electron system. This stability is maintained, if
possible, and therefore substitution is the most likely mode of reaction (1). Since the
π cloud is electron rich, benzene is susceptible to ‘attack’ by electrophilic
reagents. (1).
H
NO2
NO2
NO2+
+
+
H+
(3)
[5]
(b)
(c)
(i)
Nitrobenzene is reduced to phenylamine using tin (1) and hydrochloric acid
(1).
Phenylamine is treated at around 5 oC (1) with sodium nitrite (1) and
hydrochloric acid (1) to produce benzenediazonium chloride.
[5]
(ii)
A chromophore is a group responsible for colour in a compound (1).
Sudan 1 is red in white light as it is transmitting red light (1) and the other
colours / blue are absorbed (1). When blue light is shone on Sudan 1, the
blue light is absorbed and no light is transmitted and so the dye appears to be
black (1).
[4]
Mole ratio
1 mole acid chloride ≡ 1 mole chloride ions. (1)
Number of moles of AgCl
No. of moles of RCOCl =
Acid chloride is RCOCl
R is CH3CH2
=
3.87
=
143.5
0.0270
(1)
mass
mass
250
∴ Mr of ROCl =
=
= 92.6 (1)
Mr
no. of moles
0.0270
∴ R = 92.6 – (12.0 + 16.0 + 35.5) = 29.1
Formula of acid chloride is CH3CH2COCl
(1)
(1)
[5]
(QWC)
• information organised clearly and coherently, using specialist vocabulary when
appropriate (1)
[1]
Total [20]
GCE CHEMISTRY Specimen Assessment Materials 145
GCE CHEMISTRY
UNIT TEST
Year of Examination (Specimen)
Page 1 of 2
Session: summer/winter
Assessment Objective
A2 Unit CH4
Target Totals
Question
Number
1 (a) (i) I
Specification
Reference
11.2d
AO1
AO2
AO3
Total
Mark
25
45
10
80
Other requirements
Synoptic
Quality of
written
commun.
9
1
1 (a) (i) II
11.2d
1 (a) (i) III
13f
1 (a) (ii)
10a
1
1 (b) (i) I
11.2f
1
1 (b) (i) II
11.2f
1
1 (b) (ii)
11.2b
2
1 (c)
13c
2
1 (d)
11.3b i
2 (a)
10g
2 (b) (i)
10g
2 (b) (ii)
13e
1
2
9
2
2
1
1
2 (c) (i)
1
2 (c) (ii) I
10j
1
2 (c) (ii) II
10j
1
2 (d)
2 (e) (i)
Paper
9
1
11.1e
9
2
2 (e) (ii)
2
9
3 (a) (i)
2
9
3 (a) (ii)
14b
3 (b) (i)
12e
3 (b) (ii)
12f
Raw
Totals:
2
1
1
9
GCE CHEMISTRY Specimen Assessment Materials 146
GCE CHEMISTRY
UNIT TEST
Year of Examination (Specimen)
Page 1 of 2
Session: summer/winter
Assessment Objective
A2 Unit CH4
Target Totals
Question
Number
3 (b) (iii)
AO1
AO2
AO3
Total
Mark
25
45
10
80
Specification
Reference
10d
3
3 (c)
11.1e
2
3 (d)
10b
2
3 (e)
14a
4 (a) (i)
10h
2
13d
4 (a) (iv)
11.1b ii
11.1a / 14b
9
9
2
3
2
9
5
5a
10e/g/i
5
5b (i)
12a/d
3
2
5 (b) (ii)
9c /d
2
2
5 (c)
11.3b iii
1
3
2
25
45
10
Raw
Totals:
9
3
3
4 (a) (iii)
Other requirements
Synoptic
Quality of
written
commun.
2
4 (a) (ii)
4b
Paper
9
9
GCE CHEMISTRY Specimen Assessment Materials 147
MARK SCHEME
SPECIMEN PAPER
CH5
Range of acceptable answers.
The answers given in the marking schemes in this Specimen Assessment Materials document are
suggestions that would be acceptable to the Chief Examiner. However, alternative answers that are
correct and relevant to the question are to be given appropriate credit by markers.
Assessment of Quality of Written Communication (QWC) in AS/A Chemistry
Answers to questions, whether in one sentence or in a paragraph, will be assessed as to whether
the candidate has communicated the appropriate chemistry clearly and unambiguously.
Candidates will need to
(i)
(ii)
(iii)
ensure that text is legible and that spelling, punctuation and grammar are accurate so
that meaning is clear;
select and use a form and style of writing appropriate to purpose and to complex
subject matter;
organise information clearly and coherently, using specialist vocabulary when
appropriate.
The inclusion of (QWC) in the marking schemes indicates to markers where the quality of a
candidate’s written communication will be awarded marks.
GCE CHEMISTRY Specimen Assessment Materials 148
SECTION A
Answer all the questions in the spaces provided.
1.
(a)
Dynamic equilibrium is when the rate of the forward reaction is equal to the rate of
the reverse reaction so there is no net change in concentration / pressure. (1)
[1]
(b)
(i)
Kc =
(ii)
I
[ NH 3 ] 2
[ N 2 ][H 2 ]3
[N2] =
4 .0
2 .0
[H2] =
[NH3] =
II
(1)
2 .0
2 .0
= 1.0 mol dm-3
=
2.0 mol dm-3
(1)
0.5 × 1.0 × (2.0)3 = 2.0 mol dm-3
(1)
[2]
2.0 dm3 of 1.0 mol dm-3 N2 contain 4.0 mol N
2.0 dm3 of 2.0 mol dm-3 NH3 contain 4.0 mol N
∴50% Ν present as N2
(c)
[1]
(1)
(1)
[2]
(i)
2nd order with respect to NO
[1]
(ii)
1st order with respect to Cl2
[1]
(iii)
3rd order
[1]
(iv)
ON…..Cl……..Cl……NO
(1) for two NO and one Cl2 in the diagram, in any configuration
(1) for one NO either side of the Cl2 molecule
[2]
(d)
Property of the reaction
Activation energy of the
forward reaction
The rate of the forward
reaction
Temperature increase
NE
2 marks for 4 correct, (1) for 2 correct
I
Addition of a catalyst
D
I
[2]
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 149
2.
(a)
(i)
Cl2 + 2NaOH → NaCl + NaClO + H2O
(1)
3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O
(1)
NaClO produced by cold , dilute NaOH (1), NaClO3 by warm, conc NaOH (1)
(ii)
(b)
NaClO / ClO– +1
NaCl / Cl– –1
(1) for each of two from three
NaClO3/ ClO3– +5
[4]
[2]
(i)
Inert pair effect / 6s2 electrons not involved in bonding (1)
Covalent bonding a weaker option for lead / stronger option than inert pair
effect for carbon
(1)
[2]
(ii)
I
Pb2+(aq) + 2OH–(aq) → Pb(OH)2(s)
(1)
Pb(OH)2(s) + 2OH–(aq) → [Pb(OH)4]2–
(1)
White ppt forms which redissolves to give a colourless solution (1)
II
Pb2+(aq) + 2I–(aq) → PbI2(s)
Yellow ppt forms
[3]
(1)
(1)
[2]
Total [13]
GCE CHEMISTRY Specimen Assessment Materials 150
3.
(a)
A weak acid is one which is only slightly / partially dissociated into H+ ions
(1)
[ H + ][CH 3 COO − ]
[CH 3 COOH]
[1]
(b)
Ka =
(c)
Weaker since Ka smaller / less dissociation (or converse)
(d)
(i)
Curve II
(1)
which has the largest jump in pH at the endpoint (strong acid v strong base)
(1)
[2]
(ii)
Curve III
(1)
pH at end point ~ 8 / has the highest starting pH (weak acid)
(1)
[1]
(1)
[1]
(iii)
Curve III
(1)
which requires the largest volume of alkali at the endpoint (1)
(iv)
25.0 cm3 of 0.10 mol dm-3 base reacts with 20.0 cm3 acid (1)
So acid concn =
25.0 × 0.10
= 0.125 mol dm-3
20.0
(1)
(1)
[2]
[2]
[2]
Mark consequentially if wrong curve or endpoint chosen.
(e)
A buffer solution is one whose pH changes negligibly upon the addition of small
amounts of acid or base.
[1]
(f)
No moles acid =
5
= 8.33 × 10-2
60
8.33 × 10 −2
= 0.833 mol dm-3
Conc acid =
0.100
(1)
(1)
[2]
Total [14]
GCE CHEMISTRY Specimen Assessment Materials 151
SECTION B
(a)
4.
Any 5 × (1) from the following
group 3 atoms only have three outer electrons
can only form three covalent bonds
simple compounds only have six outer electrons / do not have a stable outer octet
dimerisation involves coordinate covalent bonds from Cl to Al
description or diagram to show the correct dimer structure
many donor – acceptor complexes involve coordinate covalent bond from group 5 to
group III atom
example of donor-acceptor complex such as NH3.BF3
Cl– bonding to AlCl3 by coordinate bonding (or equivalent)
[5]
AlCl4– present in some ionic liquids (with large organic cation)
(QWC)
• legible text and accurate spelling, punctuation and grammar so that meaning is
clear (1)
• a coherent and clearly expressed response using a style appropriate to complex
subject matter (1)
[2]
(b)
(i)
B
B
B
B
B
N
N
N
N
N
B
B
B
B
B
N
N
N
N
N
B
B
B
B
N
N
N
N
N
B
B
B
B
B
N
N
N
Any 3 × (1) for
(1) for alternate B & N atoms in hexagonal rings
(1) for layer structure
(1) for weak intermolecular forces between layers
(1) for isoelectronic / same structure as graphite
(1) for not having delocalised electrons because N
is more electronegative than B
N
[3]
(QWC)
• information organised clearly and coherently, using specialist vocabulary when
appropriate (1)
[1]
(ii)
Each layer “bends” so that opposite edges bond to form a cylinder.
[1]
(iii)
Any one from
lubricant / wear-resistant coating / drill tips / furnace linings
nanotubes as sleeving / catalyst support / semiconductors
[1]
GCE CHEMISTRY Specimen Assessment Materials 152
(c)
(i)
ΔH = ΔHfo H2O(g) + 2ΔHfo BN(s) − ΔHfo B2O3(s) − 2ΔHfo NH3(g)
= 3 (−241.8) + 2(−254.4) − (−1272.8) − 2 (−46.1)
=
(ii)
+ 130.8 kJ mol-1
ΔG =
(1)
(1)
[2]
ΔH − TΔS
ΔG = + 130.8 − 873 ΔS
ΔS
=
=
=
3(188.7) + 2(14.8) − 2(192.3) − (54.0)
+ 157.1 J mol-1 K-1
(1)
+ 0.1571 kJ mol-1 K-1
ΔG = + 130.8 − 873 (0.1571)
= + 130.8 − 137.1
= − 6.3 kJ mol-1
(1)
ΔG negative, so reaction will occur.
(1)
[3]
(Mark consequentially)
(iii)
Gases have higher entropies than solids
(1)
because the freedom of the atoms / molecules is not so restricted as in solids
(1)
[2]
Total [20]
GCE CHEMISTRY Specimen Assessment Materials 153
5.
(a)
(i)
All electrodes are measured against the standard hydrogen electrode (1)
which is defined as having zero value.
(1)
[2]
(ii)
Positive EMF, + 0.56V, so reaction is spontaneous (1)
6 Fe2+ + Cr2O72– + 14H+ → 6Fe3+ + 2Cr3+ + 7H2O
(iii)
Mean titre = 26.02(5) cm3 (third titre too far out to use)
Conc Fe2+ =
(iv)
(v)
26.025 × 0.0200 × 6
= 0.125 mol dm-3
25.0
4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H2O
(1)
[2]
(1)
[2]
(1)
(1)
Overall reaction 2H2 + O2 → 2H2O EMF + 1.23V
Forward (exothermic) reaction used to produce power / heat
Reverse (endothermic) reaction used to store energy
(vii)
[2]
(1)
Mr (NH4)2Fe(SO4)2.6H2O = 392.1 g mol-1
(1)
2+
-3
≡
1 AIS 1 Fe , so conc = 0.125 × 392.1 g dm = 49.0 g dm-3
(Mark consequentially)
Positive EMF, + 0.46V, so reaction occurs to form Fe3+
(vi)
(1)
[2]
(1)
(1)
(1)
[3]
2 × (1)
Advantage:
“Clean” technology with water as only product / convenient method of
storing energy etc.
Disadvantage:
Energy is lost as storage cycle not 100% reversible / problems of storing
gases / run at low temperatures etc.
[2]
(b)
(i)
Iron(II) cation
1s2 2s2 2p6 3s2 3p6 3d6 (or equivalent “electrons in boxes”)
(1)
3d and 4s electrons involved in bonding
3d and 4s levels very similar in energy / different numbers of electrons can be
removed
Bonding can be ionic or covalent
Any 2 points from three × (1)
[3]
(ii)
[Fe(H2O)6]2+
octahedral
(1)
[FeCl4]–
tetrahedral
(1)
[2]
Total [20]
GCE CHEMISTRY Specimen Assessment Materials 154
WELSH JOINT EDUCATION COMMITTEE
CYD-BWYLLGOR ADDYSG CYMRU
General Certificate of Education
Tystysgrif Addysg Gyffredinol
MARK SPECIFICATION GRID
GCE CHEMISTRY
UNIT TEST
Year of Examination (Specimen)
Page 1 of 2
Session: summer/winter
A2 Unit
Assessment Objective
CH 5
Target Totals
Question
Number
1a
Specification
Reference
20.1
AO1
AO2
AO3
Total
Mark
25
45
10
80
Other requirements
Synoptic
Quality of
written
commun.
9
9
1
1bi
20.1
1
1 b ii I
20.1
2
1 b ii II
20.1
2
1ci
18
1
1 c ii
18
1
1 c iii
18
1
1 c iv
18
2
1d
18
2
2ai
16.4
4
2aii
16.4
2
2bi
16.3
2
2biiI
16.3
2
1
2biiII
16.3
1
1
3a
20.2
3b
20.2
1
3c
20.2
1
3di
20.2
1
3dii
20.2
2
3diii
20.2
3div
20.2
3e
20.2
3f
20.2
Raw
Totals:
Paper
13
9
13
1
1
2
2
1
2
14
9
9
GCE CHEMISTRY Specimen Assessment Materials 155
GCE CHEMISTRY
UNIT TEST
Year of Examination (Specimen)
Page 2 of 2
Session: summer/winter
Assessment Objective
A2 Unit CH 5
AO1
AO2
AO3
Total
Mark
25
45
10
80
Target Totals
Questio
n
Number
4a
Paper
Other requirements
Synoptic
Quality of
written
commun.
9
9
Specification
Reference
9
16.2
7
4bi
16.2
4
4 b ii
16.2
4 b iii
16.2
4ci
19.1
4 c ii
19.2
4 c iii
19.2
5ai
15.1
5 a ii
15.1
2
5 a iii
15.2
2
5 a iv
15.2
2
5av
15.1
2
5 a vi
15.1/15.3
3
5 a vii
15.3
9
1
1
2
3
2
20
2
2
9
5bi
17
3
5 b ii
17
2
20
45
80
Raw
Totals:
GCE Chemistry SAMs (2009-2010)/JD
23 February 2009
25
9