Download CHEMISTRY

EUROPEAN BACCALAUREATE 2011
CHEMISTRY
DATE: 7 June 2011
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 2011: CHEMISTRY
Question A1
Page 1/3
Marks
a)
Mandelic acid, 2-hydroxy-2-phenylethanoic acid, can be obtained pure from
bitter almonds.
The structural formula of mandelic acid is given below:
Mandelic acid can be found in certain skin care products. For example, it is
used to treat acne.
100 cm3 of an aqueous solution of mandelic acid contains 1.59 g of mandelic
acid.
The pKa of mandelic acid is 3.85 at 25.0 oC.
i. Calculate the molar molecular mass of mandelic acid.
1 mark
Given:
Molar atomic masses (in g mol-1)
H : 1.01 ; C : 12.0 ;
O : 16.0
ii. Calculate the concentration (in mol dm-3) of this mandelic acid solution.
2 marks
iii. Calculate the pH of this mandelic acid solution at 25.0 oC.
3 marks
iv. Use the structure to explain why mandelic acid is soluble in water.
2 marks
v. Explain why mandelic acid is more soluble in an aqueous alkaline
solution.
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A1
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Marks
b)
The concentration of mandelic acid taken from another cosmetic product
is determined by titration using a solution of sodium hydroxide, NaOH(aq).
pH
VNaOH / cm3
The graph above shows the titration of 25.0 cm3 of this cosmetic product with
1.20 x 10-1 mol dm-3 sodium hydroxide solution.
It is assumed that mandelic acid is the only acid in this cosmetic product.
i. Give the equation for the titration using structural formulas.
2 marks
ii. State the pH at the equivalence point and the volume of solution of base
added at the equivalence point.
2 marks
iii. Calculate the concentration (in mol dm-3) of the mandelic acid in this
cosmetic product.
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A1
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Marks
iv. Suggest an appropriate indicator from the table below for this titration.
Explain your choice.
Indicator
pH range
thymol blue
1.2 – 2.8
bromophenol blue
3.0 – 4.6
phenolphthalein
8.3 – 9.8
v. What data concerning the acid can be obtained from the pH value at the
half-equivalence point?
c)
2 marks
1 mark
It is necessary to use a buffer solution in order to maintain a constant pH in
cosmetic products containing mandelic acid.
i. Suggest how a buffer solution using mandelic acid could be prepared (it
is not necessary to include a calculation).
2 marks
ii. In which pH region will this buffer solution be effective?
2 marks
iii. Give equations to show how this buffer solution works when an acid or a
base is added.
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A2
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Marks
a)
Fuel cells are used in spacecraft as a source of electrical energy. Some of
these cells use hydrogen, H2(g), and oxygen, O2(g), as reactants. The gases
diffuse through a porous carbon electrode and react in a basic solution.
Platinum is used to catalyse the reaction.
Given : Standard redox potentials for the relevant couples :
E / V
Couple
b)
H2O(l) / H2(g)
– 0.83
O2(g) / OH-(aq)
+ 0.40
i. Identify the type of reaction which occurs at the positive electrode and
give the corresponding half-equation.
2 marks
ii. Give the half-equation for the reaction occurring at the negative
electrode.
1 mark
iii. Give the overall equation for the reaction occurring in the fuel cell.
1 mark
iv. Explain how the pH changes around each half-cell as the cell works.
2 marks
v. Calculate the e.m.f. of the cell under standard conditions.
1 mark
Fuel cells have recently been made using a basic solution of hydrazine,
N2H4(aq), and oxygen, O2(g), as reactants.
The relevant half-equations are:
N2H4(aq) + 4OH-(aq) ⇌ N2(g) + 4H2O(l) + 4eO2(g) + 2H2O(l) + 4e- ⇌ 4OH-(aq)
i. Give the equation for the overall reaction taking place in the cell.
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1 mark
EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A2
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Marks
ii. Does hydrazine act as an oxidising agent or as a reducing agent in this
reaction? Explain your answer using oxidation numbers.
2 marks
iii. Calculate the volume of oxygen gas used in one hour when the cell
operates under standard conditions to produce a steady current of
500 mA.
3 marks
Given :
The molar volume of a gas under standard conditions : 24.5 dm3 mol-1
1 Faraday = 9,65 x 104 C mol-1
c)
A chemist wished to convert chloride ions, Cl-(aq), into chlorine, Cl2(g).
i. From the table below, which is the most suitable reagent to perform this
experiment? Explain your answer.
2 marks
ii. Give the overall equation for the reaction.
2 marks
Given:
Standard redox potentials
d)
Reduction half-equation
EӨ / V
MnO4-(aq) + 8H+(aq) + 5e- ⇌ Mn2+(aq)+ 4H2O(l)
+ 1.51
Cl2(g) + 2e- ⇌ 2Cl-(aq)
+ 1.36
Cr2O72-(aq) + 14H+(aq) + 6e- ⇌ 2Cr3+(aq) + 7H2O(l)
+ 1.33
Bleach contains sodium hypochlorite, NaClO(aq).
Sodium hypochlorite reacts with an acidified solution of potassium iodide,
KI(aq), to give iodine, I2(aq), which can be titrated with a solution of sodium
thiosulphate, Na2S2O3(aq) of known concentration.
i. Give the equation for the reaction between ClO-(aq) ions and I-(aq) ions
in acid solution to form Cl-(aq) and I2(aq).
2 marks
ii. Give the equation for the reaction between I2(aq) and S2O32-(aq) ions to
form I-(aq) ions and tetrathionate ions S4O62-(aq).
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A2
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Marks
A 25.0 cm3 sample of the bleach was diluted to give 250 cm3 of solution.
25.0 cm3 of this solution was added to an excess of acidified potassium
iodide solution, KI(aq).
The volume of 2.00 x 10-1 mol dm-3 sodium thiosulphate solution required to
titrate this last solution was 18.5 cm3.
iii. Determine the concentration of sodium hypochlorite in this sample of
bleach.
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4 marks
EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A3
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Marks
a)
Ammonia, NH3(g), is manufactured by the Haber-Bosch process. In this
process nitrogen, N2(g) and hydrogen, H2(g) react at high pressure in the
presence of a catalyst.
Explain whether this is a redox reaction or an acid-base reaction
according to Brønsted-Lowry theory.
b)
c)
2 marks
Sodium carbonate, Na2CO3(s), can be obtained industrially by the Solvay
process.
During this process carbon dioxide, CO2(g), is passed through a saturated
solution of sodium chloride, NaCl(aq), and ammonia to produce ammonium
chloride, NH4Cl(aq), and sodium hydrogencarbonate, NaHCO3(s).
The sodium hydrogencarbonate is decomposed by heating to give sodium
carbonate and carbon dioxide among the products.
i. Give the equation for the reaction which leads to the formation of
sodium hydrogencarbonate and ammonium chloride.
2 marks
ii. Give the equation for the thermal decomposition of sodium
hydrogencarbonate.
2 marks
i. Give the equation for the preparation of ammonia from ammonium
chloride, NH4Cl(s) and calcium oxide, CaO(s).
2 marks
ii. Calculate the pH of an aqueous solution of ammonia containing 4.89 g
of ammonia in 500 cm3 of solution at 25.0 oC.
3 marks
Given:
The pKb of NH3(aq) at 25.0 oC : 4.75
Molar atomic masses (in g mol-1):
H : 1.01; N : 14.0
iii. State whether an aqueous solution of ammonium chloride is acidic,
neutral or basic. Give the relevant equation.
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2 marks
EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question A3
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Marks
d)
In 1906, Ostwald developed a method for manufacturing nitric acid,
HNO3(aq), in three successive steps.
In the first step, ammonia is combusted in oxygen, O2(g), from the air at a
high temperature (700 oC) in the presence of a catalyst to obtain nitrogen
monoxide, NO(g), and water.
In the second step, after cooling the nitrogen monoxide to 200 oC, it is
oxidised to nitrogen dioxide, NO2(g).
In the third step , nitrogen dioxide reacts with water to form nitric acid and
nitrogen monoxide.
i. Give the relevant equations for the three steps to produce nitric acid.
4 marks
ii. A factory produces 5.00 x 105 kg of pure nitric acid each day.
Calculate the volume of ammonia required under standard conditions to
obtain this mass of acid each day.
4 marks
Given :
The molar volume of a gas under standard conditions : 24.5 dm3 mol-1
Molar atomic masses (in g mol-1):
H : 1.01 ; N : 14.0 ; O : 16.0
e)
Silver, Ag(s), can react with nitric acid, HNO3(aq), to give a solution of silver
nitrate, AgNO3(aq), and nitrogen monoxide, NO(g).
i. Give the overall equation for this redox reaction.
2 marks
ii. Use the redox potentials given in the following table to explain why
gold, Au(s), does not react with nitric acid.
2 marks
Given: Standard redox potentials:
EӨ / V
Couple
Ag+(aq) / Ag(s)
+ 0.80
NO3-(aq) / NO(g)
+ 0.96
Au3+(aq) / Au(s)
+ 1.42
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B1
Page 1/2
Marks
a)
Aldehydes can be readily converted to nitriles by reacting with compound X.
Nitriles can then be hydrolysed by boiling with hydrochloric acid, HCl(aq) to
give carboxylic acids as shown below:
X

HC
l
Consider the following reactions:
A X
 B HC
l C
where C represents the compound CH3CH(OH)COOH
i. Give the IUPAC name and write the structural formula of compound A.
2 marks
ii. Give the IUPAC name of compound C.
1 mark
iii. Give the formula of the reagent X involved in the conversion of A to B.
1 mark
iv. Give the mechanism for the conversion of A to B. Use ‘curly arrows’ to
show the movement of pairs of electrons.
3 marks
Compound A can be prepared by oxidising another compound.
v. Give the IUPAC name and write the structural formula of this other
compound.
2 marks
vi. Give the IUPAC name of the product obtained by oxidising compound A
with an acidified solution of potassium dichromate, K2Cr2O7(aq).
1 mark
vii. State, with an explanation, whether compound C is a stronger or weaker
acid than propanoic acid.
3 marks
When propanoic acid is dissolved in a non polar solvent it appears to have a
molar molecular mass which is double the expected value.
viii. Suggest a reason, based on its molecular structure, to explain this
behaviour.
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2 marks
EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B1
Page 2/2
Marks
b)
Compound D has a molar molecular mass of 118 g mol-1.
The percentage composition by mass of this compound is:
C: 50.8 % ; H: 8.50 %; O: 40.7 %.
i. Show that the molecular formula of compound D is C5H10O3.
2 marks
Given :
Molar atomic masses (in g mol-1):
H : 1.01 ; C: 12.0 ; O : 16.0
Boiling compound D with sodium hydroxide solution followed by neutralisation
with acid to give compound, C, with the formula CH3CH(OH)COOH, and an
alcohol E.
ii. Give the structural formulas and the IUPAC names of compounds D and
E.
4 marks
iii. Give the equation for the reversible reaction between compounds C and
E to form compound D.
2 marks
iv. State the necessary experimental conditions for the reaction described
in b)iii. above to take place.
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B2
Page 1/3
Marks
a)
Consider the following amines:
dopamine
tyramine
adrenalin
noradrenalin
i. For each of the amines state whether it is a primary, secondary or
tertiary amine.
2 marks
ii. State the name of another functional group possessed by all these four
amines.
1 mark
iii. Explain whether noradrenalin or tyramine will be more soluble in water.
2 marks
iv. Explain why the pKb of noradrenalin (pKb = 5.42) is higher than the pKb
of adrenalin (pKb = 4.84).
2 marks
.
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B2
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Marks
b)
Consider the following amino acids:
glycine (Gly)
alanine (Ala)
phenylalanine (Phe)
i. Explain why the pKa of the –COOH functional group of alanine is lower
than that of propanoic acid.
2 marks
ii. Glycine and propanoic acid have virtually identical molar molecular
masses. Explain why the melting point of glycine is very much higher
than the melting point of propanoic acid.
2 marks
Alanine can show optical activity and amphoteric behaviour.
iii. Define the two underlined terms.
2 marks
iv. Show the three-dimensional representations of the two enantiomers of
alanine.
1 mark
v. Explain why glycine does not exhibit optical activity.
1 mark
vi. Give appropriate equations to illustrate the amphoteric behaviour of
alanine in aqueous solution.
2 marks
The primary structure of a tripepetide is Ala-Gly-Phe
vii. Give the simplified structural formula of this tripeptide formed from the
condensation of these three amino acids.
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2 marks
EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B2
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Marks
c)
Kevlar is an example of a synthetic polymer formed from the reaction of 1,4diaminobenzene and benzene-1,4-dicarboxylic acid.
i. Give the structural formulas of 1,4-diaminobenzene and benzene-1,4dicarboxylic acid
2 marks
ii. Give the simplified structural formula of the repeating unit of Kevlar.
2 marks
iii. Explain why Kevlar is water resistant but is dissolved by acid.
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B3
Page 1/2
Marks
a)
One of the essential fatty acids is linoleic acid. This acid cannot be
synthesised by the human body and therefore must come from food.
The formula of linoleic acid is shown below:
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
The degree of unsaturation of linoleic acid can be determined by the addition
of iodine, I2(aq).
The iodine number represents the mass (in grams) of iodine which adds to
100 g of an unsaturated compound.
i. Give the equation for the reaction of iodine with linoleic acid.
2 marks
ii. Calculate the iodine number for linoleic acid.
3 marks
iii. Give the simplified formula of the triglyceride formed between
propane-1,2,3-triol and linoleic acid.
2 marks
iv. Show that the iodine number of the triglyceride obtained in a) iii. is 174.
1 mark
Given :
Molar molecular masses (in g mol-1):
linoleic acid : 280 ; triglyceride of linoleic acid : 878
Molar atomic mass (in g mol-1):
I : 127
Hydrogenation can be used to decrease the degree of unsaturation of certain
oils during the production of margarine.
Generally triglcerides in margarine have an iodine number of about 85.
v. Assuming that the triglycerides present in margarine have a similar
molar molecular mass to the triglyceride of linoleic acid, state the
number of C=C double bonds present in a molecule of a margarine
triglyceride.
1 mark
vi. Explain the difference in melting points between the starting oil and the
partially hydrogenated fat.
2 marks
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EUROPEAN BACCALAUREATE 2011: CHEMISTRY
Question B3
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Marks
b)
Complete hydrogenation of the triglyceride of linoleic acid leads to the
formation of the triglyceride of octadecanoic acid.
This product can be used to make soap.
i. Give the equation for the saponification reaction using structural
formulas and give the IUPAC names of the products of the reaction.
4 marks
ii. Calculate the volume of 10.0 mol dm-3 potassium hydroxide solution,
KOH(aq), required to saponify 1.00 x 103 kg of the triglyceride of
octadecanoic acid.
2 marks
Given:
Molar molecular mass (in g mol-1):
triglyceride of octadecanoic acid : 890
c)
In aqueous solution soaps form an emulsion with fats.
i. With the help of a labelled diagram explain how soap acts as an
emulsifier.
3 marks
ii. Explain why hard water prevents soap from working.
2 marks
iii. Why do synthetic anionic detergents work effectively in hard water
conditions?
1 mark
iv. State the disadvantages of using synthetic detergents.
2 marks
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