Download CHEMISTRY

EUROPEAN BACCALAUREATE 2010
CHEMISTRY
DATE: 11th June 2010
DURATION OF THE EXAM :
3 hours (180 minutes)
PERMITTED MATERIAL :
Calculator (not graphical and not programmable)
INSTRUCTIONS :
 Answer two A questions and two B questions.
 Indicate which four questions you have answered by putting crosses in
the appropriate place on the sheet supplied.
 Use a separate answer sheet for each of the four main questions.
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EN
EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A1
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Marks
a)
Certain flowers such as hydrangeas, display various colours due to the
presence of natural coloured pigments. The appearance of the colours red,
mauve, violet and blue are due to the presence of anthocyanins in the petals.
The violet colour is attributed to the molecule shown below, which is
represented as HA in the questions which follow.
HA can be present as two acid-base couples H2A+(aq) / HA(aq) with
pKa1 = 4.3 and HA(aq) / A–(aq) with pKa2 = 7.0.
H2A+(aq) is red, HA(aq) is violet and A–(aq) is blue.
The value of pKw = 14.0.
i. Define an acid according to Brønsted theory.
1 mark
ii. Identify the acid and the base forms for each of the two couples using
the simplified formulas given above.
2 marks
iii. Write the equation showing the reaction when the acid HA(aq) reacts as
an acid with water.
1 mark
iv. Give the expression for the acid dissociation constant Ka2 for HA(aq).
1 mark
v. Determine the value of Ka2
1 mark
b) The pH of a solution containing HA(aq) is 10.0.
i. From the expression for Ka2 calculate the ratio [A-(aq)]eq
2 marks
[HA(aq)]eq
ii. Deduce the predominant species present and state the colour of the
solution.
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2 marks
EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A1
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Marks
c)
A-(aq) and HA(aq) can react as Brønsted bases.
i. Give the equation for the reaction of HA(aq) behaving as a base with
water.
ii. Give the expression for the base dissociation constant Kb1 for this
reaction.
iii. Prove that Ka1 x Kb1 = Kw
1 mark
2 marks
3 marks
iv. Reproduce the diagram below.
pKa1
pKa2
4.3
7.0
pH
Show on the diagram where the species H2A+(aq), HA(aq) and A–(aq)
predominate and show the colours of the flowers as a function of pH.
v. Explain why the flowers of hydrangeas can change colour according to
the nature of the soil.
d)
2 marks
2 marks
Magnesium ammonium phosphate is a sparingly soluble salt which can be
formed in urine and is also known as ‘uric acid stone’ in medicine. The
formation of the salt can be described by the following simplified equation.
Mg2+(aq) + NH4+(aq) + HPO42-(aq) + H2O(l)
MgNH4PO4 (s) + H3O+(aq)
i. Describe the effect of changing the pH on the formation of the salt.
2 marks
ii. Using the values of Ka and Kb, write the equation for the dominant
reaction that takes place when the HPO42-(aq) ion is present in water.
1 mark
iii. By referring only to the reaction in d) ii. Calculate the pH of a solution of
hydrogenphosphate ions, HPO42-(aq), when the initial concentration of
the ions [HPO42-(aq)] is 1.50 x 10-3 mol dm-3.
2 marks
Given : Ka (HPO42-): 4.30 × 10-13
Kb (HPO42-): 1.60 × 10-7
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A2
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Marks
a)
Two half-cells involving the couples Fe3+(aq)/Fe(s) and Fe2+(aq)/Fe(s) are
joined together to produce an electrochemical cell.
N.B. The values needed can be found at the end of part c).
b)
i. Write the half-equations for the chemical reactions taking place at the
electrodes.
2 marks
ii. Give the overall equation for the reaction taking place in the cell.
1 mark
iii. Calculate the electromotive force (e.m.f.) of the cell operating under
standard conditions.
1 mark
iv. Draw a labelled diagram of the cell and show the direction of electron
flow in the external circuit.
3 marks
Potassium manganate(VII), KMnO4(aq), is an oxidising agent.
2 marks
Explain why it is not used to determine quantitatively the amount of Fe(II)
ions in a solution of Fe(II) chloride?
c)
Equal volumes of equimolar solutions of potassium manganate(VII),
KMnO4(aq), manganese(II) sulphate, MnSO4(aq), potassium dichromate(VI),
K2Cr2O7(aq), and chromium(III) sulphate, Cr2(SO4)3(aq) are mixed and
allowed to come to equilibrium.
i. State which ion is oxidised and which ion is reduced.
2 marks
ii. Using the half-equations, write the equation for the overall reaction.
3 marks
Given : Standard redox potentials :
Couple
E / V
MnO4-(aq), H+(aq) / Mn2+(aq)
+ 1.51
Cl2(g) / Cl-(aq)
+ 1.36
Cr2O72-(aq), H+(aq) / Cr3+(aq)
+ 1.33
Fe3+(aq) / Fe2+(aq)
+ 0.78
Fe3+(aq) / Fe(s)
- 0.04
Fe2+(aq) / Fe(s)
- 0.44
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A2
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Marks
d)
The most important ores of aluminium and iron comprise of Al2O3 and
Fe2O3 respectively.
Aluminium is obtained from its ore by electrolysis.
Iron is obtained from its ore by heating with carbon monoxide, CO(g). During
this process the carbon monoxide is converted into carbon dioxide, CO2(g).
i. Give the equation for the reduction of aluminium ions during the
electrolysis of aluminium(III) oxide.
The unbalanced equation below
iron(III) oxide and carbon monoxide:
Fe2O3(s) + CO(g)
represents
→
the
reaction
1 mark
between
Fe(s) + CO2(g)
ii. Determine the oxidation numbers of carbon and iron.
2 marks
iii. Give the balanced equation for the reaction.
1 mark
iv. Calculate the mass of iron that could be obtained from 4.50 kg of iron
ore containing 80.0% by mass of Fe2O3 assuming that the remaining
20.0% contains no iron.
3 marks
v. Calculate the charge in coulombs (C) necessary to produce 2.00 kg of
aluminium during the electrolysis of its oxide.
3 marks
vi. If a current of 2.00 x 104 A is used calculate the time it takes to produce
2.00 kg of aluminium by electrolysis of Al2O3.
1 mark
Given: Molar atomic masses (in g mol-1):
O: 16.0
Al: 27.0
Fe: 56.0
1 Faraday (F): 9.65 x 104 C mol-1
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A3
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Marks
a)
A patent for a zinc bromide rechargeable battery was registered with the
European Patent Office in 1992.
The following experiment shows the recharging process of this battery:
an aqueous solution of zinc bromide is electrolysed using graphite
electrodes.
i. Draw a labelled diagram of the cell during the recharging process.
2 marks
ii. Give the half-equations for the reactions taking place at each of the
electrodes and specify the polarity of the electrode associated with
each half-equation.
2 marks
iii. Give the overall equation for the reaction occurring during the
recharging of the battery.
1 mark
iv. Calculate the electromotive force (e.m.f.) when the battery is
discharging under standard conditions.
1 mark
v. In the design given in the patent the container of the battery is made of
poly(ethene) and the electrodes are made of graphite.
2 marks
Explain the choice of these two materials based on their chemical
properties.
Given: Standard redox potentials
EӨ / V
Couple
b)
Zn2+(aq) / Zn(s)
– 0.76
Br2(l) / Br-(aq)
+ 1.07
Cl2(g) / Cl-(aq)
+ 1.36
Swimming pools can be disinfected using a product called ‘bromine sticks’.
The active ingredient in this product has the formula C5H6BrClN2O2.
i. Calculate the percentage by mass of bromine in the active ingredient.
2 marks
ii. One product of the disinfection process is bromide ions. Use the
relevant standard redox potentials to explain what might happen if the
pool has also been treated with chlorine, Cl2(g). Include the relevant
equation in your answer.
2 marks
Given: Molar atomic masses (in g mol-1):
H : 1.01 C : 12.0 N : 14.0 O : 16.0 Cl : 35.5
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Br : 79.9
EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A3
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Marks
c)
The ideal pH for swimming pool water is between 7.2 and 7.6. In order to
maintain the correct pH compounds containing hydrogencarbonate ions,
HCO3-(aq), can be added.
i. Write the equations which show how hydrogencarbonate ions can
control the pH within the region given.
2 marks
Excess acid can be removed by running the water over a marble, i.e. a
calcium carbonate, CaCO3(s), bed.
ii. Write an equation to show the neutralisation action of marble with an
acid.
1 mark
iii. Calculate the mass of calcium carbonate required to increase the pH of
2.00 x 103 m3 of pool water from 6.5 to 7.2.
4 marks
Given: Molar atomic masses (in g mol-1):
C : 12.0
d)
O : 16.0
Ca : 40.1
Small amounts of ammonium ions, NH4+(aq), are present in good quality
fresh water. However, ammonium ions react with water to form ammonia
which is toxic to aquatic life.
i. Give the equation for this reaction and state the expression for the acid
dissociation constant, Ka, for ammonium ions.
The graph below shows how the ratio of the concentrations
[NH4+(aq)]/[NH3(aq)] changes with temperature, θ (in oC), and pH value.
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2 marks
EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question A3
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Marks
ii. Use the graph to explain what happens to the quality of the water if the
temperature θ increases within the pH range 8.0 to 11.0.
2 marks
iii. Use the graph to calculate the value for the acid dissociation constant of
ammonium ions, Ka, at temperature θ = 0 oC.
2 marks
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B1
Page 1/2
Marks
a)
Many aldehydes have very strong and characteristic smells. This is the
case for cinnamaldehyde, the major component of cinnamon, and vanillin
responsible for the characteristic smell of vanilla pods.
A molecule of cinnamaldehye contains one benzene ring and also contains
one carbon to carbon double bond.
i. A sample of cinnamaldehyde contains 81.8% carbon, 6.10% hydrogen
and 12.1% oxygen by mass.
3 marks
Determine the empirical formula of cinnamaldehyde.
ii. The molar mass of cinnamaldehyde is 132 g mol-1.
1 mark
Determine the molecular formula of cinnamaldehyde.
iii. Give one possible structural formula of cinnamaldehyde.
2 marks
Given: Molar atomic masses (in g mol-1):
H: 1.01
b)
C: 12.0
O: 16.0
The structural formula of vanillin is given below:
i. The molecule of vanillin contains two other functional groups apart from
an aldehyde. State the names of these two other groups.
2 marks
ii. Vanillin can react with ethanol in the presence of concentrated sulphuric
acid. Give the equation for this reaction using structural formulas.
3 marks
iii. Vanillin can also react with ethanoic acid. Give the equation for this
reaction using structural formulas.
3 marks
iv. When vanillin reacts with Fehling’s solution it forms a carboxylate anion.
4 marks
State what will be observed during the reaction and give the equation
for the reaction.
v. Vanillin can react with an acidified solution of hydrogen cyanide,
HCN(aq). Give the mechanism for this reaction.
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3 marks
EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B1
Page 2/2
Marks
c)
Vanillin can react with a basic solution of silver nitrate.
The simplified equation for this reaction is given below:
C6H3OHOCH3CHO(aq) + 2Ag+(aq) + 3OH-(aq) →
C6H3OHOCH3COO-(aq) + 2Ag(s) + 2H2O(l)
A sample of a food additive containing vanillin has a mass of 2.40 x 10-3 g.
2.55 x 10-3 g of silver are formed when the sample undergoes the reaction
above.
i. Calculate the percentage by mass of vanillin in the sample.
3 marks
ii. State the assumption made during the calculation.
1 mark
Given:
Molar atomic mass (in g mol-1):
Ag: 108
Molar molecular mass of vanillin (in g mol-1): 152
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B2
Page 1/3
Marks
a)
The reaction scheme below shows the synthesis of a coloured compound, B,
starting with 4-aminobenzenesulphonic acid, H2N-C6H4-SO3H.
i. Refer to the group enclosed by the box to name the chemical family to
which compound A belongs.
1 mark
ii. Name the type of reaction for the synthesis of compound B and state
the chemical family to which this coloured compound belongs.
2 marks
iii. Explain, by referring to its molecular structure, why compound B is
coloured.
3 marks
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B2
Page 2/3
Marks
b)
c)
Consider the following nitrogen-containing compounds:
A.
(CH3)3N
B.
C6H5NH2
C.
CH3(CH2)2NH2
D.
CH3CH2NHCH3
E.
NH3
i. For each amine state whether it is primary, secondary or tertiary.
3 marks
ii. Name compounds B and C.
2 marks
iii. Among the five compounds above, compound B, C6H5NH2, is the
weakest base. Explain why.
2 marks
Captopril® is a medicine used to control high blood pressure. It possesses
an amide group and can be synthesised from the two molecules A and B
below:
i. Name the oxygen-containing functional group in molecule A.
1 mark
ii. Does molecule A exhibits optical isomerism? If so, draw the molecule
and identify the chiral carbon atom with an asterisk (*). Explain your
answer.
2 marks
iii. Knowing that one of the products is hydrogen chloride, HCl(g), and
using structural formulas, write the overall equation for the reaction
between A and B to form Captopril®.
2 marks
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B2
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Marks
d)
The IUPAC name of the amino acid leucine is 2-amino-4-methylpentanoic
acid.
i. Give the simplified structural formula for a molecule of leucine.
1 mark
ii. Explain the term ‘isoelectric point’ of an amino acid.
1 mark
iii. The isoelectric point of leucine is 6.0.
3 marks
Give the simplified structural formulas of the major species present in
aqueous solutions of leucine with the following pH values.
1o) pH = 6.0
2o) pH = 1.0
3o) pH = 13.0
iv. By referring to its molecular structure explain why leucine is a solid at
room temperature (25 oC).
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2 marks
EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B3
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Marks
a)
The structure formulas below are of the molecules of two lipids, X and Y.
One of the lipids is a fat (solid) the other is an oil (liquid).
X
Y
i. Name the functional group common to compounds X and Y.
1 mark
ii. Name the two reactants necessary to make compound X.
2 marks
iii. Indicate which of the two compounds X or Y is an oil.
3 marks
Explain why it is a liquid at room temperature.
iv. Oils, such as vegetable oils, can be modified chemically to make
margarine, that is they can be turned into fats (solids).
Name the chemical reagent necessary to carry out this transformation.
b)
1 mark
Compound Y can react with iodine, I2(aq).
During this reaction the brown colour of the iodine solution disappears.
i. Explain how compound Y reacts with iodine.
2 marks
ii. Calculate the mass of compound Y that reacts completely with 100 g of
iodine.
3 marks
Given:
Molar atomic mass (in g mol-1):
I: 127
Molar molecular mass of compound Y (in g mol-1): 878
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B3
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Marks
c)
d)
Compound X can react with potassium hydroxide, KOH(aq), to form a soap.
i. Give the equation for this reaction using simplified structural formulas
and name the type of reaction that takes place.
3 marks
ii. Using a diagram, explain the detergent properties of soaps.
3 marks
iii. Explain why the soap obtained in c) i. is not so efficient in hard water,
i.e. in the presence of a relatively high concentration of calcium ions,
Ca2+(aq).
1 mark
After a certain time fats and oils turn rancid.
Generally these unpleasant smells are due to the oxidation of the fatty acids.
The addition of molecules called ‘antioxidants’ can help prevent rancidity.
The structural formulas of two antioxidants are shown below:
BHT
THBQ
i. Name a functional group that is common to these two compounds.
1 mark
ii. Explain, in terms of their molecular structures, why both of these
antioxidants are soluble in fats and oils.
1 mark
iii. Only one of these compounds is also slightly soluble in water.
State which of the two compounds this is and explain this difference in
solubity.
2 marks
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EUROPEAN BACCALAUREATE 2010: CHEMISTRY
Question B3
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Marks
e)
Ascorbic acid, known as Vitamin C, is another example of an antioxidant.
It has the following structure:
When it functions as an antioxidant the ascorbic acid molecule loses two
hydrogen ions, H+(aq) from the two hydroxyl groups, –OH, attached to the
ring.
Using structural formulas write the corresponding half-equation for this
oxidation process.
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2 marks