Download sec chemistry may 2011 marking scheme

UNIVERSITY OF MALTA
SECONDARY EDUCATION CERTIFICATE
SEC
CHEMISTRY
May 2011
MARKING SCHEME
MATRICULATION AND SECONDARY EDUCATION
CERTIFICATE EXAMINATIONS BOARD
Marking scheme – May 2011 Paper 1
Section A
1
boils
increases
steam
dissolves
solvent
solute
electricity
Total
2
(a)
(b) (i)
(ii)
incomplete dissociation / ionization of the molecules
Accept produces few H+ ions
in solution / in water
sodium chloride/ potassium sulfate
1
1
1
1
1
1
1
7 marks
½
½
ammonia solution
1
1
1
do not accept zinc oxide
(c)
In water
H+ /H+ (aq)/ H3O+ (aq)
Cl- / Cl- (aq)
½
½
ignore ions from water
In methylbenzene
HCl
1
DO NOT accept HCl (aq)
Total
3
(a)
Mg + 2HCl →MgCl2 + H2
(b)
(c) (i)
(ii)
5 marks
2
all symbols correct award 1
balancing correct award 1
gas syringe or syringe / calibrated gas jar / inverted measuring
cylinder
Do not accept measuring cylinder
Moles HCl = 20/1000 x 0.15
½
= 0.003
½
2 moles HCl : 1 mole H2
½
moles H2 = 0.0015
½
Vol H2 = 0.0015 x 22.4
½
3
= 0.0336 dm
½
Accept 0.034 dm3
If not all the steps are shown, but some of the steps leading to a
correct answer, award the 2 marks
Total
1
1
1
2
6 marks
4
(a)
Structure of methoxymethane, CH3OCH3
(b)
1
Formula or structure of organic
product
1
(i)
C3H7OH + concentrated C3H6 or structure
H2SO4
C3H7ONa/ C3H7O- Na+
(ii) C3H7OH + sodium metal or structure
C3H7Cl or structure
(iii) C3H7OH + PCl5
1
1
white fumes/ white misty fumes / fumes
(c)
5.
Do not accept effervescence
Total
(a) (i)
(ii)
(b) (i)
(ii)
6.
1
5 marks
conc H2SO4 + KCl(s) →KHSO4 (s) + HCl(g)
all correct formulae award 1
do not accept K2SO4
correct state symbols award 1
Forms dense white fumes (½) with ammonia (½)/
forms fumes of ammonium chloride (½) with ammonia (½) /
turns moist blue litmus (½) red (½).
Accept white ppt with AgNO3
2
hydrogen is lost/ oxidation state of chloride (or chlorine) is
increased/ oxidation state of Mn(IV) is reduced / Cl- lost electrons
accept half-equation
bleaching of hair/ swimwear/ skin conditions/ respiratory problems/
etc
bleaching associated (½) with presence of HOCl (½) /
medical conditions (½) associated with HOCl (½)
Total
1
1
1
1
6 marks
(a)
High pressure
low temperature
1
1
(b)
Solid CO2 : weak intermolecular forces or Van der Waals forces
1
1
(c)
Diamonds: macromolecular structure
Strong / covalent bonds (½) need to be broken (½)
diamond: compact while graphite: layered / hexagon structure
1
½x2
OR
diamond: 4 bonds per C atom; graphite 3 bonds per C atom
OR diamond : no delocalized e-s ; graphite delocalized e-s
2
½x2
½x2
Total
1
6 marks
7
(a) (i)
(ii)
carbon dioxide/ CO2
1
Turns lime-water milky
1
(iii) Ba2+ (aq) + SO42-(aq) → BaSO4(s)
2
Sulfate ion identified 1
Ionic equation correct and all state symbols correct award 1
(b) (i)
(ii)
cation in Q is Al3+ / Zn2+
1
if charge is missing award ½
cation in T is Pb2+
1
if charge is missing award ½
Total
8
6 marks
(a) (i)
moles Na = 2.3/23
½
= 0.1
½
if not all steps are shown but answer correct award 1
1
(ii)
moles O2 = 1.12/ 22.4
½
= 0.05
½
if not all steps are shown but answer correct award 1
1
(iii)
O2 : 2O
0.05 : 0.01
moles oxygen atoms = 0.1
1
(b)
(c)
Na : O
0.1 : 0.1
0.1 : 0.1
ratio Na:O = 1 :1
E.F. = NaO
½
½
2
½
½
½
½
if not all steps are shown but answer correct award 2
mass of E.F = 39
½
Ratio formula mass to E.F. mass =2
½
Chemical formula = Na2O2
1
if not all steps are shown but answer correct award 2
Total
3
2
7 marks
9
(a)
cars / internal combustion engine
1
(b) (i)
(ii)
SO2 / CO2 / O3 / CH4 / CFCs
Depending on the answer in (b)(i):
power stations/ combustion of fossil / factories / volcanoes – SO2
cars / power stations/ combustion of fossil fuels / factories – CO2
cars / combustion of fossil fuels –O3
decomposition of organic material – CH4
Aerosols, refrigerants – CFCs
1
1
(c)
Depending on the answer in (b)(i):
respiratory problems / acid rain / skin or eye irritation – SO2
greenhouse effect / global warming – CO2
respiratory problems – O3
greenhouse effect – CH4
depletion of ozone layer – CFCs
1
(d)
CO + N2O → CO2 + N2
OR
2CO + 2NO → 2CO2 + N2 OR
4CO + 2NO2 → 4CO2 + N2
2
all symbols correct award 1
balancing correct award 1
Total
10 (a)
6 marks
2
to show eight electrons around each iodine atom
½x2
sharing of electrons shown in a reasonable manner
1
if proper sharing of electrons not shown do not award 1
(b)
(c)
Weak (½) intermolecular forces (½) or Van der Waals’ forces
a lattice (½) of positive ions (½)
1
2
delocalized electrons/ sea of electrons/ free
electrons from outer shells
award 1
If diagram is correct but no labeling given
award 1
(d)
Copper contains mobile/delocalized electrons
iodine has no free ions/ no free electrons/ is covalent
4
award ½
award ½
Total
1
6 marks
Section A
11 (a) (i)
(ii)
(orange or yellow) / (smoky or sooty) / luminous
any two 1 x 2
Do not accept bright flame
high C:H ratio / unsaturated / presence of triple bond
2
2C6H14 + 13 O2 → 12CO + 14H2O
2
1
all symbols correct award 1
balancing correct award 1
(iii) C6H14
C9H18
1
1
2
(iv) propene
1
reasonable structure showing the double bond
1
if structure incorrect but double bond shown award ½
2
(b) (i)
Substitution / free-radical substitution
Do not accept halogenation or chlorination
1
(ii)
C2H6 + Cl2 → C2H5Cl + HCl
accept products CH3CH2Cl + HCl
all symbols correct award 2
2
Formula of ALL products correct but formulae of reactants incorrect
award 1
Accept correct multiple substitutions
(iii) UV / diffused sunlight / light / photo-catalyzed
Accept heat but not high temperatures
(c) (i)
(ii)
Any valid representation of CH3CHClCH2Cl
all bonds shown
if more than 2 atoms missing in the structure
addition reaction
1
award 1
award ½
1
(d) (i)
(ii)
addition of several monomers (½) with no loss of any atoms (½)
Any reasonable representation showing two units only
if {two units}n is given
award ½
(iii) No
It is not biodegradable/ resistant to chemicals/ lasts for a long time/
animals may ingest it after granulation
(iv) bottles/ packaging/ toys/ construction materials/ piping/ wire coatings
/ plastic bags
Do not accept plastic
Total
5
1
1
1
1
1
1
20 marks
12 (a) (i)
N2 + 3H2
2
2NH3
but if
(ii)
(b) (i)
(ii)
all symbols correct award 1
balancing correct award 1
sign not shown award 1 ½
400 - 500 oC
200 – 350 atmospheres
1
1
Pt and Rh catalyst
2NO(g) + O2(g)
1
2
2NO2(g)
all symbols correct award 1
balancing correct award 1
Ignore if
not shown
2
4NO2 + 2H2O + O2 → 4HNO3 OR
2NO2 + H2O → HNO3 + HNO2
all symbols correct award 1
balancing correct award 1
(c) (i)
ΔH is change in (½) enthalpy/ energy / heat (½)
1
represents dynamic equilibrium / equilibrium / reversible
(ii) brown colour increases/ intensifies
equilibrium shifts to the right / forward reaction favoured / more NO2
forms
(iii) brown colour decreases/ fades / turns colourless
1
1
1
Formula mass (NH4)2SO4 = 28 + 8 + 32 + 64 = 132
1
% nitrogen = 28 x 100/ 132
½
= 21%
½
If some steps in the working are missing but ans is correct award full
marks
3CuO(s) + 2NH3(g) → 3Cu(s) + N2(g) + 3 H2O(l)
all symbols correct award 1
balancing correct award 1
2
NH3 is oxidized OR CuO is reduced
1
(d)
(e) (i)
(ii)
½
1
2
because NH3 lost hydrogen / oxidation state of nitrogen increased /
nitrogen lost electrons / CuO lost oxygen / O.S. of copper decreased
½
(iii) black solid decreases/ pink solid formed / condensation on some parts
of apparatus
Total
6
1
20 marks
Marking Scheme - May 2011 Paper 2A
Section A
1
a
Different atoms of the same element having the same number of
protons (or proton number)
½
but different number of neutrons (or mass number) in their nuclei
½
1
If ‘same element’ is omitted or ‘two elements’ given deduct
½ mark.
79
81
atom Br ion Br
b
c
protons
35
35
neutrons
44
46
electrons
35
36
½x6=
3
Award marks for correct values only.
RAM = [(79*51) + (81*49)] / 100
= 80
1
1
2
All the steps must be shown to obtain any marks.
Total
2
a
b
c
d
Zn2+
= +2
H
=0
Loses
Oxidised
Gain
Reduced
Zn → Zn2+ + 2e2H+ + 2e- → H2
½
½
½
½
½
½
1
1
1
2
2
Accept as correct if the equations are given with the electrons
being subtracted instead of added.
No
Total
6 marks
1 1
6 marks
3
ΔHc, is the amount of heat given out when 1 mole of substance is
completely burnt in oxygen (or excess air).
a
C3H8 + 5O2 → 3CO2 + 4H2O
Balanced equation
Correct symbols
3 mol of CO2 = 1 mol C3H8
moles of C3H8 = 4.5 / 3 = 1.5 mol
ΔHc for C3H8 = 3300 / 1.5
= - 2200 kJ mol-1
b
½
½
1
½
½
½
½
1
1
4
Deduct 1 mark if the answer does not include a negative sign.
If not all the steps are shown but some of the steps lead to the
correct answer award full marks.
C3H8 + 5O2 or Energy level of reactants Energy c
CO2 + 4H2O or 2
Energy level
of products Progress of reaction Each correct axis
Each correctly labeled energy level
½
½
Total
4
a
i
ii
b
i
ii
iii
c
Allotropes are different forms of the same element
in the same state.
Rhombic
Monoclinic
Oxidizing agent
Dehydrating agent
(No marks for drying agent as answer)
As an acid
Accept any one of the following:
Vulcanization of rubber / agriculture / matches / gunpowder / etc\
Do not accept: contact process /manufacture of sulfates/ fertilizer.
Total
2 7 marks
½
½
½
½
1
1
1
1
1
1
6 marks
Copper (II) sulfate-5-water is dissolved in water
Award marks if dissolution omitted but students indicates use of
solution.
Magnesium metal is added to the solution.
½
Any one of the following:
• Pink deposit of copper
• Magnesium dissolves
• Blue solution gets paler / colorless solution.
1
Mg + CuSO4→ Cu + MgSO4
5
All symbols correct
½
1
a
3
Alternative answer
1
Heat / react magnesium with copper (II) oxide.
Do not accept ‘mix’
Any one of the following:
• A violent reaction occurs
• Pink copper forms
• Black colour of copper(II) oxide disappears
• White magnesium oxide forms
Mg + CuO → Cu + MgO
•
•
•
b
1
All symbols correct
calcium oxide
is added to warm dilute nitric acid
until excess solid remains.
•
•
•
The solid is filtered off.
The filtrate is added to sodium carbonate solution.
Calcium carbonate precipitate is filtered off.
In the last step the student must indicate
formation of ppt or filtration to get ½ mark.
Do not accept CaO with H2SO4.
Total
3 1
½
½
½
½
½
½
3
6 marks
6
½x4=
2
a
b
c
d
i
ii
Award ½ mark for each correct charge.
Award ½ mark for each correct diagram.
Ionic or electrovalent bonding
It is the electrostatic attraction between oppositely charged ions.
Do not accept a bond between metal and non-metal.
Na2O
Award ½ mark for MgO.
Covalent bonding
Accept any two of the following:
• SiO2 has a giant (or macromolecular) covalent structure
• Silicon and oxygen atoms are held together by very strong
covalent bonds.
• These bonds require very high temperature/energy to break.
Total
1
1
1
2
1
1
½x2=
1
7 marks
1
7
a
b
2
i
1
1
Butanoic acid
Esterification
ii
All formulae correct
Equilibrium sign
1
1
1
2
Any of the following:
iii
•
•
•
Neutralizes the butanoic acid
Removes the smell of the acid
Makes it possible to smell the fruity ester.
1
Total
4 6 marks
8
a
The reaction would be to violent / Na too reactive / rxn dangerous
Only award marks for the drawing and/or labelling of the
following:
c
½
½
½
½
• Combustion tube / glass tube (drawn and labeled)
• Boat containing solid CuO (drawn and labeled)
• Heating the CuO
• Burning excess hydrogen.
Any one of the following:
b
i
ii
1
• Does not produce CO2, which is a greenhouse gas
• Non-pollutant / clean fuel
• Renewable fuel
• Saves on fossil fuels
Any one of the following:
•
•
•
1
High cost of hydrogen.
Hydrogen cannot be liquefied at room temperature.
Dangerous gas (explosive)
1
Total
A = CaCO3 (do not accept ‘calcium cabonate’)
A = limestone
9
a
2
5 marks
½
½
B = Ca(OH)2
B = slaked lime
Do not award marks for lime water.
2
½
½
CaCO3 (s) + H2O (l) + CO2 (g) → Ca(HCO3)2 (aq)
b
•
•
c
•
•
Balanced equation and all formulae correct
All state symbols correct
1
1
Boiling the tap water / Distill (Do not accept heat)
thermally decomposes the Ca(HCO3)2 OR (produces CO2
gas, water and calcium carbonate)
CaCO3 precipitates out of solution
The suspension is filtered to remove the CaCO3 OR water
collected as distillate
½
½
Total
5 ½
½
2
2
6 marks
10
a
i
ii
iii
b
i
ii
Oxygen
Approximately 79 cm3
1
1
Accept ans as percentage
• Oxygen reacts with carbon
• forming gaseous CO2
Nitrogen
Any two of the following:
• Unreactive / does not react with food
• Removes O2 / slows the bacterial growth / slows the decay
of the food / keeps food fresh / food preservation.
• Slows the oxidation of food / retains the flavour of the food
• Liquid N2 used to fast freeze food.
Total
6 ½
½
1
1
½x2=
1
5 marks
Section B
11
a
i
ii
A catalyst is a substance that
• Alters / increases the rate of reaction but
• is still present at the end of the reaction / without being
used up
Deduct 1 mark for ‘Does not take part in the reaction’
• During the reaction oxygen is produced / increase in
volume.
1
1
2
½
•
•
•
A known volume of hydrogen peroxide
is placed in container connected to a gas syringe
a small amount of MnO2 is added.
½
½
½
•
•
The reaction is left for a fixed amount of time
the volume (of oxygen produced) is measured at several
intervals.
½
½
3
Award marks if the sections in bold are mentioned
Accept correct if the decrease in mass of hydrogen peroxide is
followed (no gas syringe but must include balance)
iii
b
i
ii
c
i
ii
iii
Correct x-axis
Correct y-axis (Do not accept
‘products)
Each correctly labelled curve
Or a relevant graph showing a decrease in the mass of hydrogen
peroxide.
The decrease in the concentration of the reactants with time or the
increase in the concentration of products with time.
• particles move faster (or higher kinetic energy) / more
collisions.
• particles collide with more energy
• more of the collisions result in a reaction / more successful
collisons (Do not accept ‘makes rxn faster’)
Decrease
Increase
5 minutes
The rate of reaction approximately doubles when the temperature
increases by 10 oC
7 ½
½
3
1, 1
1
1
1
1
3
1
1
1
1
2
d
i
ii
Any of the following:
• The rate of reaction increases in the presence of sunlight/
light.
• Light is a form of energy and therefore it increases the rate
of reaction / the energy of the reactants increases.
• Reaction is photo-catalysed.
The green colour of the chlorine gas disappears as the reaction
proceeds.
2
1
Faster
½
F2 more reactive / better oxidizing agent
½
iii
1
Total
12
a
i
ii
iii
iv
v
b
i
ii
iii
A compound that contains only carbon and hydrogen atoms.
• Carbon can catenate / form chains of C atoms
• An atom of carbon can form stable (or strong) covalent
bonds with other carbon atoms.
Gases (or fuel gas) (Do not accept LPG)
Petrol (or gasoline) / naphtha
Any two from:
• different sized molecules / different RMM / more or less
(carbon) atoms (in molecules) / different structures. Ignore
different densities.
• fuels have different boiling points
• fuels condense at different temperatures.
Cracking is the process where
• large hydrocarbon molecules are broken into smaller
hydrocarbon molecules.
• High temperatures
• High pressure / a catalyst
C10H22 → C8H18 + C2H4
Accept other correct equations
The greenhouse effect / global warming
No
Crude oil is a non-renewable resource
Any two from:
• Toxic carbon monoxide gas is given off / formation of
carboxy haemoglobin / does not allow O2 to reach brain
• Inefficient use of the fuel / not all the energy of the fuel is
used)
• Soot produced / impurities remain
8 20 marks
1
1
1
½
½
1
2
1
1x2=
2
1
½
½
3
1
1
½
½
1
1x2=
2
c
i
ii
iii
C9H18O6
RMM = (12*9)+(1*18)+(16*6) =
= 222
½
½
1
If not all the steps are shown but some of the steps lead to the
correct answer award full marks.
3 moles of gases are produced.
3 * 22.4 dm3 =
67.2 dm3
1
½
½
V1 / T1 = V2 / T2
T2 = 273 + 500 = 773K (award ½ for 273 and ½ for 500)
V2 = (67.2 / 273) * 773
= 190 dm3
1
½,½
½
½
Total
13
a
i
i
iii
iv
v
b
i
A = Chlorine
B = Hydrogen
C = Sodium hydroxide
2Cl- → Cl2 + 2e-
2
2
3
20 marks
1
1
1
3
All symbols correct
Balancing correct
Accept as correct if the equations are given with the electrons
being subtracted instead of added.
2H+ + 2e- → H2
All symbols correct
Balancing correct
Accept as correct if the equations are given with the electrons
being subtracted instead of added.
Q = IT
Q = 86500 * 3600 = 3.114 x 108 C
1
1
2
1
1
2
no of moles of electrons = 3.114 x 108 / 96500
= 3227 moles
2 mol of e : 1 mol of Cl2
Moles of Cl2 = 3227 / 2 = 1614 moles
Mass of Cl2 = (1614 * 71) / 1000
= 114.6 kg
Deduct 1 mark if the answer is given in grams.
Any one of the following:
• Sterilizing potable water / Manufacture of bleaching
products
• Production of plastics (such as PVC)
• Extraction of Bromine
½
½
½
½
1
1
9 1
2
3
1
Semi-permeable membrane / asbestos or polymer membrane
(award ½ mark for ‘membrane’ only or diaphragm)
ii
iii
c
i
ii
1
½
½
+
It allows Na ions from the brine to pass through
Na+ combines with the OH- ions forming NaOH.
Manufacture of paper / soaps / detergents / Purification of bauxite/
Production of Aluminium / absorption of acidic gases - industrial
Drain cleaning agents – domestic
As a strong alkali / neutralization of acids / tests for cations - lab
Hydrogen chloride
1
1
1
a
i
Acid / detect ammonia
ii
iii
A solution of known concentration.
• A substance which ionizes completely in water
• to give OH- ions.
C2O4H2.2H2O
RMM = (12*2)+(16*4)+(1*2)+(18*2) =
= 126
If not all the steps are shown but some of the steps lead to the
correct answer award full marks.
moles of C2O4H2
= 1.85 / 126
= 0.0147 mol
1
20 marks
1
½
½
1
1
i
ii
1
1
1
2
1
Do not award marks if measuring cylinder / teat pipette is given.
moles of C2O4H2 in 25 cm3 = 0.0147 / 10 = 0.00147 mol
1 mole of C2O4H2 : 2 moles of NaOH
1
1
moles of NaOH in 15 cm3 = 0.00147 * 2 = 0.00294 mol
conc of NaOH = (0.00294 * 1000) / 15
= 0.196 mol dm-3
1
1
1
If not all the steps are shown but some of the steps lead to the
correct answer award full marks.
Deduct ½ mark if no suitable units are given.
2
2
If not all the steps are shown but some of the steps lead to the
correct answer award full marks.
Detect the end-point / stop the titration
Accept ‘to indicate complete neutralization’
No
Gradual changes in colour / no sharp end-point
Pipette / bulb pipette / graduated pipette
iii
iv
1
1
1
iv
b
3
1
Total
14
2
10 5
•
c
i
•
CO2 is absorbed by the solution. (award the ½ mark if CO2
only is mentioned)
Reacts with NaOH to give the carbonate.
ii
Neutralisation reaction
2NaOH (aq) + CO2 (g) → Na2CO3 (aq) + H2O (l)
Balanced equation
All state symbols correct
iii
Exothermic
Total
11 ½
½
2
1
1
1
2
1
20 marks
Marking Scheme – May 2011 Paper 2B
SECTION A
1
a i
5 neutrons
ii 6 neutrons
b i
6 electrons
ii No charge, neutral
c
(10 X 1) + (11 X 4)
1 + 4
= 10.8
1
1
1
1
1
Total
2
a
i
ii
b
3
i
ii
a
b
c
d
2H+ + CO32- → H2O + CO2
All formulae correct
All charges correct
1
1
All formulae correct
All charges correct
Hydrogen / H+ / Hydrogen ions
Do not Accept H2
Reduction in oxidation state of hydrogen, Gain of electrons by the hydrogen
ions
Total
1
1
1
1
Zn + 2H+ → Zn2+ + H2
a
i
ii
b
c
i
6 marks
1 mole of C3H8 = (12 X 4 + 1 X 8) = 44 g
?
=
66 g
½
½
66/44 =
1.5 moles
1.5 moles = 3330 KJ
1 mole
= ?
3330
= 2220 KJ mol-1
1.5
The quantity of heat released when 1 mole of substance
is completely burned in excess of air
Exothermic
½
½
½
½
Total
4
1
6 marks
When an element is present in 2 or more different forms
without a change of state
Rhombic
Monoclinic (needle shape)
Accept plastic sulfur
Accept any three of the following:
Oxidizing agent
Dehydrating agent
Drying agent
Acid.
Accept to make sulfates.
One out of:
agriculture / gunpowder / matches / vulcanization of rubber
Total
1 ½
½
1
5 marks
½
½
1
1
1x3
1
7 marks
5
a
b
i
ii
i
ii
iii
Sodium
Silver
Forms very strong bonds with other elements
that are not easily broken
or
Forms stable compounds that are difficult to reduce.
Rubidium
Zn + 2AgNO3 → Zn(NO3 )2 + 2Ag
1
1
½
½
Correct Equation
Correct Balancing
Total
6
1
1
6 marks
a
Correct Structure
Correct Bonding
b
i
Red litmus – no change
Blue litmus to red
ii
Inverted funnel + labelling
(Beaker / test-tube) with water + labelling
Inverted funnel touching the water
½,½
1
½
½
Total
7
a
b
Ethanoic acid
Effervescence / gas evolved (or given off)
c
CH3COOH + CH3OH
1
1
CH3COO CH3 + H2O
Accept molecular formulae
Conc. H2SO4 OR Dry HCl
Sweet / fruity smell/characteristic smell of ester
d
e
Correct formulae
Equilibrium sign
Total
8
a
b
c
i
ii
Copper is less reactive than hydrogen or
Copper is below hydrogen in the reactivity series or
Copper cannot displace hydrogen from an acid
Two of: fume cupboard
Safety glasses / gloves / lab coat (Accept only one safety wear)
No flames in proximity of the gas
Make small volumes
One of: It does not cause any pollution
A renewable source of energy
Saves on fossil fuels
Accept: does not produce greenhouse gases
One of:Too costly to produce
Explosive (Too dangerous)
Cannot be liquified at rtp
2 1
1
1
1
6 marks
1
1
1
1
1
Total
½,½
½,½
1
6 marks
5 marks
9
a
b
Substance A = calcium oxide / quicklime
Substance B = calcium hydroxide / slaked lime / lime water
i
ii
iii
1
1
CaCO3 + H2O + CO2 → Ca(HCO3)2
Advantage = provides calcium important for bones and teeth
Disadvantage = Furring / wastage of soap / blocking pipes / scaling
Sodium carbonate OR washing soda OR Na2CO3.10H2O / Na2CO3
Total
10
a
b
i
ii
iii
i
ii
Oxygen / O2
Approximately 79 cm3
Ozone
Nitrogen
Any two of the following:
• Unreactive / does not react with food
• Removes O2 / slows the bacterial growth / slows the decay of the food
/ keeps food fresh / food preservation.
• Slows the oxidation of food / retains the flavour of the food
• Liquid N2 used to fast freeze food.
Do not accept ‘not to crush food’
Total
3 2
1
1
1
7 marks
1
1
1
1
1
1
6 marks
11
a
i
SECTION B
A substance that
Alters / increases the rate of the reaction
Is still present at the end of the reaction
1
1
Deduct 1 mark for ‘Does not take part in the reaction’
ii
Axis
Correct position of graphs and labelling
iii
b
i
ii
SO3 – Vanadium pentoxide / Vanadium(V) oxide
NH3 – Iron
Surface area
Heat / increase in temperature
Increase concentration
1,1
1 ½, 1 ½
1
1
1
1
1
Accept catalyst
iii
Axis
Correct position of graphs – shape
c
i
ii
Any of the following:
• The rate of reaction increases in the presence of sunlight /light.
• Light is a form of energy and therefore it increases the rate of reaction
/ the energy of the reactants increases.
• Reaction is photo-catalysed.
Yellow green colour fades
iii
Do not accept white fumes of HCl / explosion
Faster
Total
4 1,1
1,1
2
1
1
20 marks
12
a
b
i
ii
A = Concentrated NaCl / brine
B = Hydrogen
Substance C = Sodium hydroxide
2Cl- - 2e → Cl2
iii
2H+ + 2e → H2
i
86500 x 60 x 60
= 311400000C
1 mole = 96500C
? = 311400000C
311400000/96500
=3227 mol
2 moles of e
→
1 mole of Cl2
3226.94moles →
? moles
3226.94/2
= 1613.5 moles of Cl2
1 mole of Cl2 = 35.5 x 2 = 71g
1613.47 moles
=
1613.47 x 71
114556 g OR 114.6 kg
One of : Hydrogen chloride/Hydrochloric acid
Manufacture of plastics PVC
Manufacture of bleaching products/Bleaching Agent
Sterilizing of water
Extraction of Bromine
Industrial use: Manufacture of paper OR Manufacture of soap OR
Purification of bauxite/Production of Aluminium
Domestic use: Drain cleaner/unblocker
Laboratory use: Neutralization of acids / alkali
Hydrogen chloride (No marks given for giving Hydrochloric acid as
answer)
Production of hydrochloric acid / acid
ii
iii
iv
c
i
ii
d
i
ii
Correct equation
Correct Balancing & Charges
Correct Equation
Correct Balancing & Charges
1
1
½
½
1
1
1
1
1
1
1
Total
5 1
1
1
1
1
1
1
1
1
1
20 marks
13
a
b
i
Fractional Distillation
A=Gas fuel / gas
B=Petrol / gasoline / naphtha
C=Fuel Oil / oil
D=Asphalt / paraffin wax / tar / lubricating oil
1
1
1
1
1
ii
1, 1
1, 1
iii
iv
c
d
ii
ii
iii
No marks awarded for structures with carbon and/or hydrogen having
the incorrect number of bonds
Half a mark is awarded if basic chain is correct but hydrogen atoms not
written down
Any one of:
Kerosene = aircraft fuel
Paraffin oil = heating oil
CH4 + 2O2 → CO2 + 2 H2O
For using CH4
Correct equation and balancing
Catalytic cracking OR Cracking
• High temperatures
• High pressure / a catalyst
No
Crude oil is a non-renewable resource or similar
Carbon monoxide
Any two form
• Toxic carbon monoxide gas is given off / formation of carboxy
haemoglobin / does not allow O2 to reach brain
• Inefficient use of the fuel / not all the energy of the fuel is used
• Soot produced / impurities remain
6 1
1
1
1
1
½
½
1
1
1
Total
1,1
20 marks
14
a
i
ii
iii
b
i
ii
iii
iv
v
vi
RMM of Na2CO3 = 106
1 mole = 106g
0.5 moles = ?
106 x 0.5 =
53g
Any three of the following:
Balance = to weigh the solid
Volumetric flask = to make a solution of 1 dm3
Watch glass/petri dish/weighing boat = to weigh 53g of solid
Funnel = to transfer solid to beaker
Wash bottle = to wash apparatus that contained solid
Beaker / flask = to carry out the dissolving
Stirrer = to dissolve the solid
Two out of;
all watch glass/petri dish and funnel are washed properly
all washings go into the beaker
when the solution is made to the mark the reading is taken at eye-level
precise weighing
1000 cm3 = 0.5 moles
25 cm3 = ?
25 x 0.5
1000
= 0.0125 moles
½
½
½
½
1,1
1,1
1,1
1,1
1
1
1 mole of Na2CO3 reacts with 2 moles of HCl
0.0125 moles
reacts with 2 x 0.0125 moles
0.025 moles
½
½
34.5 cm3 = 0.025 moles
1000 cm3 = ?
1000 x 0.025
34.5
= 0.72 mol dm-3
1
1
To determine the end point / stop the titration
No
Gradual changes in colour / no sharp end-point
The volumetric pipette is used to measure the 25 cm3 of Na2CO3
and transfer it into the conical flask
The burette is used to measure the volume of acid
that is required to neutralize the Na2CO3
Total
7 1
1
1
½
½
½
½
20 marks