2013 Y6 H2 Chem QP

1

Raffles Institution 2013 9647/Y6/T3/13 [Turn Over

RAFFLES INSTITUTION 2013 YEAR 6 TERM 3 COMMON TEST Higher 2

CHEMISTRY 9647

4 July 2013

2 hours 30 minutes

Additional Materials: OMR Answer Sheet Writing Papers Data Booklet

READ THESE INSTRUCTIONS FIRST DO NOT open this booklet until you are told to do so. Write your name and civics tutorial group in the spaces provided on the cover sheets on pages 11 and 27. This paper consists of three sections A, B and C. Section A (20 marks) consists of 20 multiple-choice questions. Record your answers to this section in soft pencil on the separate OMR Answer Sheet. Section B (35 marks) consists of 4 structured questions. Answers to this section are to be written in the spaces provided in the question paper. Section C (40 marks) consists of 2 free-response questions. Answers to this section are to be written on the writing papers provided. You are to begin each question on a fresh page of paper. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. Write in dark blue or black pen. You may be subject to penalty for writing answers in pencil.

This document consists of 27 printed pages.

2


Section A (20 marks)

For each question, there are four possible answers, A, B, C and D. Choose the one you consider to be correct and record your choice on the OMR Answer Sheet provided. 1 The values of some thermochemical data for barium chloride are given in the table

below.

Lattice energy of barium chloride = 2065 kJ mol1

Standard enthalpy change of hydration of barium ions = 2494 kJ mol1

Standard enthalpy change of hydration of chloride ions = 363 kJ mol1

What is the standard enthalpy change of solution of barium chloride?

A 5285 kJ mol1 B 4922 kJ mol1

C 1155 kJ mol1 D 792 kJ mol1

2 The enthalpy change of neutralisation between aqueous sodium hydroxide and

hydrochloric acid is 57.2 kJ mol1, but the enthalpy change of neutralisation

between aqueous sodium hydroxide and ethanoic acid is 55.2 kJ mol1.

Which statement best explains the numerical difference between these values?

A The ionisation of ethanoic acid to give hydrogen ions in water is an

endothermic process.

B Aqueous ethanoic acid contains fewer hydrogen ions than hydrochloric acid of

the same concentration.

C The reaction between aqueous sodium hydroxide and aqueous ethanoic acid

produces less than 1 mole of water.

D A smaller volume of aqueous ethanoic acid than that of aqueous hydrochloric

acid of the same concentration is required for the neutralisation.

3 Which statement about the equilibrium shown below is correct?

[Fe(H2O)6]3+(aq) + H2O(l) [Fe(H2O)5OH]

2+(aq) + H3O+(aq) H > 0

lilac orange A The equilibrium constant has no units.

B The solution turns lilac when pH is increased.

C The equilibrium constant increases when the mixture is diluted.

D The rate constant of the backward reaction increases with temperature.

3


4 A gaseous reactant, R was injected into a vessel and allowed to reach equilibrium

with its gaseous product, P. The production of P is endothermic.

The following graph shows the change in concentrations of R and P with time.

Which of the following changes occurred at t2?

A More R was added.

B The temperature was increased.

C An inert gas was added at constant pressure.

D The volume of the vessel was reduced at constant temperature.

5 A pure sample of NH3(g) is introduced into an evacuated vessel of constant volume.

This vessel is maintained at constant temperature such that the equilibrium below is

established.

2NH3(g) N2(g) + 3H2(g)

The value of the final pressure is then found to be 40% greater than if only NH3 were

present. What is the mole fraction of H2 in the reaction mixture?

A 0.14 B 0.28 C 0.43 D 0.71

6 A 25.0 cm3 sample of 0.35 mol dm3 HCOOH is titrated with 0.20 mol dm3 KOH.

What is the pH of the solution after an equal volume of KOH has been added to the

acid? Given: Ka (HCOOH) = 1.77 104 mol dm3.

A 3.75.1/0.075 B 3.88pH C 8.50pH D 11.74pH

time / min

concentration

t1 t2 t3

4


7 A diprotic acid H2A has Ka1 = 1 104 mol dm3 and Ka2 = 1 10

8 mol dm3. The

corresponding base A2 is titrated with aqueous HCl, both solutions being

0.1 mol dm3. Which of the following diagrams best represents the titration curve?

A

B

C

D

8 Reaction Observation

Metal X is placed in a solution of metal ions Y2+.

X dissolves and Y2+ is displaced from the solution as Y.

Metal Y is placed in acid solution. Gas bubbles form on the surface of Y.

Metal X is placed in a solution of metal ions Z2+.

No observable reaction. There is no observable reaction.

Which reaction would not occur spontaneously?

A X(s) + 2H+(aq) H2(g) + X

2+(aq)

B Z(s) + X2+(aq) X(s) + Z2+(aq)

C Z(s) + 2H+(aq) H2(g) + Z2+(aq)

D Y(s) + Z2+(aq) Z(s) + Y2+(aq)

9 An electric current of 4 A is passed for 200 minutes through molten aluminium oxide

using inert electrodes. What will be the volume of gas liberated at s.t.p.?

A 2.8 dm3 0.125 mol x 22.4

B 5.6 dm3 0.25 mol x 22.4

C 8.4 dm3 (3/4)x0.5 mol x 22.4

D 11.2 dm3

5


10 The sketch below shows a physical property of seven consecutive elements of

Periods 2 and 3 in increasing proton number.

Which physical property does this sketch depict?

A melting point

B atomic radius

C electronegativity

D electrical conductivity

11 T, U and V are oxides of Period 3 elements. The following table lists some

properties of the oxides:

melting point / oC pH when mixed with water

T 920 13

U 1610 7

V 300 2

Which of the following represents the correct set of oxides?

T U V

A MgO Al2O3 P4O10

B SiO2 Al2O3 SO2

C Al2O3 MgO SO2

D Na2O SiO2 P4O10

proton number

6


12 Which compound will give a poor yield when synthesised directly from propene?

A 1-bromopropane B propan-2-ol

C 1-bromopropan-2-ol D ethanoic acid

13 Halogenoalkane is a starting material for synthesising Grignard reagent, which is a

useful intermediate in organic synthesis as shown below.

Which of the following is not a possible product of the following reaction?

A

B

C

D

7


14 Compound X has the following structure:

Which of the following is formed when X is heated with iodine in alkaline solution?

A

B

C

D

15 LSD is a stimulant drug that is often used by the Hippies in the 1970s. Part of the

structure of LSD is shown below.

Which of the following properties can be deduced about LSD from the partial

structure shown above?

A It is insoluble in aqueous nitric acid.

B It reacts with two moles of hydrogen bromide.

C It reacts with ethanoyl chloride to give off pungent white fumes.

D It gives off a fishy smell when heated with aqueous hydrochloric acid.

8


For each of the following questions, one or more of the three numbered statements 1 to 3 may be correct. Decide whether each of the statements is or is not correct (you may find it helpful to put a tick against the statements that you consider to be correct).

The responses A to D should be selected on the basis of

A B C D

1, 2 and 3 are

correct

1 and 2 only are correct


1 only is

correct

No other combination of statements is used as a correct response.

16 Which of the following statements regarding buffer solutions are correct?

1 A CH3COOH / CH3COO buffer can be produced by adding a strong acid to a

solution of CH3COO ions.

2 Within its effective buffering range, increasing the concentrations of the

components of a buffer solution will increase its buffering capacity.

3 If the pH of an acidic buffer solution is greater than the pKa value of the acid, it will have a greater capacity to neutralise added base than added acid.

17 Which statements are correct for a cell set up under standard conditions using the

half-cells below?

Co2+(aq) / Co(s) E = 0.28 V Sn2+(aq) / Sn(s) E = 0.14 V

1 Electrons flow in the external circuit from Co electrode to Sn electrode.

2 The concentration of Co2+(aq) will increase.

3 Reduction occurs at the Sn electrode.

18 Element Z forms a chloride ZCln. When 0.500 g of the chloride reacts with excess

silver nitrate, 1.72 g of AgCl are formed.

Another 0.500 g sample of the chloride is heated strongly. When the residue is

treated with an excess silver nitrate solution, only 1.57 g of AgCl is precipitated.

Which of the following statements about the element are correct?

1 Z burns in oxygen with a yellow flame.

2 The oxidation state of Z in the residue is +3.

3 Z is in Period 3.

9



A B C D

1, 2 and 3 are

correct



1 only is

correct

No other combination of statements is used as a correct response. 19 Which of the following naturally-occurring molecules have all of the features listed

below?

At least five chiral carbons.

At least one secondary alcohol.

Either a carboxylic acid or a carboxylic acid derivative.

1

Thromoxane (TXA2)

2

Queuosine

3

Cortisol

10



A B C D

1, 2 and 3 are

correct



1 only is

correct

No other combination of statements is used as a correct response. 20 Citric acid, which causes the sharp taste of lemon juice, has the following structure.

Which of the following reacts in a stoichiometric ratio with 1 mol of citric acid?

1 1.5 mol of Mg(s)

2 3 mol of Na2CO3(s)

3 4 mol of HCl(g)

11


RAFFLES INSTITUTION 2013 Year 6 Term 3 Common Test

H2 Chemistry

COVER SHEET

Name: ( )

CT Group:

For Examiners Use Only

Section

Marks

A / 20

B

Q1 / 10

Q2 / 8

Q3 / 6

Q4 / 11

C

Q1 / 20

Q2 / 20

Penalty (Circle) 0 / 1

Total / 95

Percentage / 100

Grade

Penalty

Incorrect number of significant figures.

Missing OR wrong units.

Answers written in pencil.

Did not start question in Section C on a fresh page.

12


Section B (35 marks)

This section consists of four questions. Answer all the questions in this section in the spaces provided.

B1 Planning (P) The Matsutake mushroom is a delicacy added to many Japanese foods. One of the

components isolated from these mushrooms is methyl cinnamate which gives these mushrooms a rich and spicy aroma. Methyl cinnamate can be prepared from cinnamic acid and methanol.

OH

O

O

O

+CH3OH+ H2O

cinnamic acid methanol methyl cinnamate

compound cinnamic acid methanol methyl cinnamate

molar mass / g mol1 148 32 162

boiling point / oC 300 65 261

melting point / oC 133 98 38

(a) 10.8 g of cinnamic acid was reacted with 30 cm3 of methanol, which was in

excess, together with about 8 to 10 drops of concentrated sulfuric acid. The volume of methanol used was about 10 times more than the actual volume needed as a reactant. The addition of concentrated sulfuric acid to the mixture was highly exothermic. The reaction mixture was then heated under reflux for about five hours before the unreacted methanol was recovered by distillation.

(i) Write a plan for the preparation of methyl cinnamate.

In your plan, you should:

give a step-by-step description of the procedures you would use to prepare methyl cinnamate, and

state the capacities of the apparatus used.

. . . . . . .

For

Examiners

Use

13


. . . . . . . . . .

(ii) Draw a labelled diagram of the assembled apparatus to show how you

would recover the remaining methanol from the reaction mixture. Indicate on your diagram the reading on the thermometer.

(iii) The excess methanol was used to drive the equilibrium position to the right. Suggest another reason why methanol was used in excess for this experiment.

. . .

[6]

For

Examiners

Use

14


(b) The methyl cinnamate was purified according to the following procedure: 1. Transfer the reaction mixture containing methyl cinnamate and unreacted

cinnamic acid to a separatory funnel.

2. Add 50 cm3 of ethoxyethane, CH3CH2OCH2CH3, to the separatory funnel.

3. Add 50 cm3 of saturated sodium hydrogencarbonate solution to the separatory funnel.

4. Shake the mixture and discard the lower aqueous layer.

5. Repeat Steps 3 and 4 until no more effervescence in the aqueous layer is

observed. Suggest why the mixture must be washed with saturated sodium hydrogencarbonate solution until no more effervescence was observed.

[1] (c)

The ethoxyethane layer was collected and dried with anhydrous calcium chloride. The ethoxyethane was then evaporated to recover the crude methyl cinnamate, which was subsequently purified by recrystallisation and air-dried. Two possible solvents, A and B can be used for the recrystallisation of methyl cinnamate. The table below gives data about the solubility of methyl cinnamate in solvents A and B.

Solubility of methyl cinnamate /g per 100 g of solvent

Temperature / oC Solvent A Solvent B

10 6.0 2.0

70 11.0 9.5

During recrystallisation, 50 g of one of these solvents was saturated with the methyl cinnamate at 70 oC and the solution was then cooled at 10 oC.

tap

stopper

ethoxyethane layer

sodium hydrogencarbonate layer

separatory funnel

For

Examiners

Use

15


(i) Explain why the use of solvent A, rather than solvent B, would lead to a lower yield of recrystallised methyl cinnamate. . . . .

(ii) Calculate the final mass of methyl cinnamate that would be obtained if solvent B was used.

[2] (d) With reference to relevant data on page 12, explain how you would check the

purity of your product.

[1]

[Total: 10]

For

Examiners

Use

16


B2 (a) Iron ore is a mixture of iron(II) and iron(III) oxides. The ore goes through a series of redox reactions in the blast furnace to extract iron.

Iron(II) oxide can be reduced by carbon or carbon monoxide as shown below.

Reaction Hr / kJ mol1 Gr

/ kJ mol1

(1) FeO + C CO + Fe +161 +114

(2) FeO + CO CO2 + Fe 11.01 5.64

(i) Given the above data, calculate the standard entropy change of

reaction, Sr, of reactions (1) and (2).

(ii) Comment and explain the difference in the values obtained in (a)(i).

. . . . . . . . .

For

Examiners

Use

17


(iii) During the extraction of iron, the interior of the blast furnace has different temperatures as shown in the diagram below. This results in different reducing agents reacting with the iron ore in different regions. Using the information on page 16, deduce which reactions, (1) or (2), will take place at 700 oC and 1500 oC respectively. Write down the reaction number in the boxes below.

[5] (b) Iron(III) oxide, Fe2O3, is also reduced by carbon monoxide in the blast

furnace. Using the following data, draw an energy cycle and calculate the standard

enthalpy change of reaction for the reduction of iron(III) oxide by carbon monoxide to extract iron.

standard enthalpy change of formation of iron(III) oxide = 824 kJ mol1 standard enthalpy change of combustion of carbon monoxide = 283 kJ mol1

[3] [Total: 8]

Reaction ____

Reaction ____

700oC

1500oC

iron slag

hot air out

hot air in

iron ore and limestone

1900oC

hot air in

For

Examiners

Use

18


B3 Selective precipitation is a technique in which one ion is selectively removed from a mixture of ions by precipitation. The numerical values of the solubility product of the sparingly soluble salts in water at 25 oC are given as follows:

Ksp of AgCl = 1.77 x 1010 ; Ksp of Ag2CrO4 = 1.12 x 10

12

A solution of AgNO3 is added slowly and continuously to a solution containing Cl

(aq)

and CrO42(aq) of concentration 0.010 mol dm3 each.

It is assumed that the addition of AgNO3 solution does not change the overall solution volume to any significant degree.

(a) Show that AgCl precipitates before Ag2CrO4.

[2] (b) Calculate the concentration of Cl when the first trace of Ag2CrO4 precipitate

appears.

[1]

For

Examiners

Use

19


(c) After the AgCl precipitate is removed and more aqueous AgNO3 is added to

the remaining solution, a suspension of reddish brown Ag2CrO4 is obtained. With the aid of equations, describe and explain what happens when dilute nitric acid is added to this suspension of Ag2CrO4.

.. .. .. .. .. .. .. .. .. ..

[3]

[Total: 6]

B4 Use of the Data Booklet is relevant to this question. (a)

The standard electrode potential of bromate(V) ions in acidic medium is represented by the equation:

2BrO3(aq) + 12H+(aq) + 10e Br2(aq) + 6H2O(l) E

= +1.52 V

(i) Draw a fully labelled diagram to show how the above standard electrode potential may be determined.

For

Examiners

Use

20


(ii) Use E data to predict and explain what might happen when a solution of acidified bromate(V) ions is added separately to the following reagents in and . Write balanced equations for any reactions that occur.

Excess aqueous potassium iodide

... ... ... ... ... ... ... ... ... ... ... ... ... ... ...

Acidified potassium dichromate(VI)

... ... ... ... ... ... ...

[6]

For

Examiners

Use

21


(b) The leadacid accumulator is a storage battery because it can be recharged. It consists of a series of cells, and each cell contains an electrolyte of sulfuric acid as well as two electrodes, one made of lead and the other, lead dioxide. The relevant reduction potentials are given below.

PbSO4(s) + 2e Pb(s) + SO4

2(aq) E= 0.13 V

PbO2(s) + 4H+(aq) + SO4

2(aq) + 2e PbSO4(s) + 2H2O(l) E = +1.47 V

(i) Write the overall equation for the reaction upon discharge, and

calculate the voltage delivered by the battery if it contains a series of 6 cells.

(ii) State the polarity (i.e. + or ) of the respective electrodes by filling up the box below.

electrode polarity

Pb

PbO2

(iii) Suggest a reason why the battery is rechargeable.

... ... ...

(iv) Explain why the measurement of the electrolyte density can be used

to indicate the extent of discharge of the cell.

... ... ...

[5]

[Total: 11]

For

Examiners

Use

22


Section C (40 marks)

This section consists of two questions. Answer all questions from this section. Begin each question on a fresh page of paper.

C1 This question is mainly about organic compounds that are found in some animals

and bacteria.

(a) Mandelonitrile is synthesised and stored in special glands by some species of millipedes such as Apheloria corrigata and Pachydesmus crassicutis. When the millipede is attacked, the stored mandelonitrile undergoes an enzyme-catalysed reaction to yield a mixture of toxic hydrogen cyanide and benzaldehye, which is ejected to ward off predators.

O

Henzyme

OH

CN

+ HCN

mandelonitrile benzaldehyde hydrogen cyanide

(i) The reverse of the above reaction can be carried out in the laboratory using a trace amount of aqueous potassium cyanide. Describe the mechanism of this reverse reaction.

Under suitable conditions, mandelonitrile can be converted into compounds

W and X as shown in the reaction scheme below.

OH

CN

mandelic acid

Cl

ClOH

NH2 O

W mandelonitrile X

(ii) With reference to the different hybridisation states of the nitrogen

atoms in the CN and NH2 groups, explain why mandelonitrile, unlike compound W, is effectively neutral and not basic.

(iii) When one mole of compound X is treated with one mole of

dimethylamine, (CH3)2NH, a neutral organic product Y is obtained. Suggest the structure for Y and explain the different reactivities of the two chlorine atoms in X.

(iv) In an experiment, 0.20 mol of compound X was added to 1 dm3 of

0.10 mol dm3 sodium hydroxide solution. Calculate the approximate pH of the resultant solution formed, with reasoning shown.

[10]

23


(b) Benzaldehyde, present in the toxic secretion of the Apheloria corrigata millipedes, is known to be repellent to ants. When treated with concentrated sodium hydroxide, benzaldehyde undergoes the following reaction first studied by Stanislao Cannizzaro in 1853:

O

H

concentrated NaOH

O

O-Na+OH+

(i) Determine the oxidation number of each of the labelled carbon atoms, , and , in the three compounds and hence, or otherwise, state the type of reaction which occurs.

(ii) Using benzaldehyde as the reactant, the mechanism for Cannizzaro reaction is shown below:

O

HOH

O-

-:OH

O

H

H

O

O-

O-

+

-OH

O-

O-

H + H2O

:O-

O-H +

H2O

O

O-

O-

+

O

O-

OH

+

Deuterium, D, is the

isotope of hydrogen.

With the aid of the above mechanism, suggest the deuterium-containing organic product(s) that would be obtained for each of the following reactions:

(1) O

Hconcentrated NaOD, D2O

(2) O

Dconcentrated NaOH, H2O

24


(iii) Suggest suitable reagents and conditions to carry out the following 3-step synthesis in which one of the steps must be the Cannizzaro reaction. Show all intermediate products formed.

O

O

O

H

H

O [7]

(c) Compound L is produced by bacterial species such as Bifidobacterium and Streptococcus. In the laboratory, it can be obtained from a six-carbon compound K.

K does not react with sodium nor phenylhydrazine. Upon analysis, it is found to contain 5.6% H and 44.4% O by mass.

When K is refluxed with aqueous sodium hydroxide and the resultant mixture distilled, the distillate does not contain any organic compound. Acidification of the residual mixture left from the distillation yields L as the only organic compound. Warming 1 mole of L with alkaline aqueous iodine produces 1 mole of ethanedioate ions and 1 mole of a yellow precipitate.

(i) Determine the molecular formula of K. (ii) Suggest a suitable structural formula each for K and L. [3] [Total: 20]

25


C2 Magainins are a class of proteins isolated from the African Clawed Frog, Xenopus laevis, found to exhibit potent broad-spectrum antimicrobial activity, and are evaluated for use as drugs for treating diseases.

A major disadvantage of using peptide-based drugs is that their properties may be lost in the body of the patient due to enzymatic hydrolysis. This may be overcome by modifying the structure of the amino acids used.

Typical proteins consist of -amino acids, so named because the amino group is on

the -carbon atom, next to the carboxylic acid group.

An -amino acid, where R is the side group.

A magainin peptide may be modified using -amino acids. A -amino acid has the

amino group on the -carbon atom, which is the second carbon atom from the acid group.

A -amino acid, where R is the side group.

(a) Draw the structure of a tripeptide that consists of all three of the following

-amino acids:

-leucine: R = CH2CH(CH3)2 -lysine: R = CH2CH2CH2CH2NH2 -glutamic acid: R = CH2CH2COOH

[1] (b) Explain how a modified peptide synthesised from -amino acids may be

resistant to enzymatic hydrolysis in the body. [1]

(c) A magainin protein can be modified by replacing some of its -amino acids

with the corresponding -amino acids, with the same R groups. Explain why such a modified protein exhibits similar biological properties.

[2] (d) Describe with an aid of a diagram, the structure of the alpha helix. [3] (e) Generally, helix structures of peptides synthesised from -amino acids are

more stable than the helix structure of a typical peptide of -amino acids. Suggest a reason for this observation.

[1]

26


(f) Aspartic acid is one of the amino acids found in a magainin peptide. Suggest a possible synthesis scheme of aspartic acid from ethene.

[6] (g) The pKa values of aspartic acid are listed below:

pK1 = 1.95 pK2 = 3.71 pK3 = 9.66

(i) Sketch the titration curve when a solution containing the following

species A+ is titrated with aqueous sodium hydroxide.

A+ (ii) Draw the structure of the most abundant species present when the

pH of an aspartic acid solution is adjusted to 2.83. (iii) Describe the movement of the species from part (ii) in an electric

field. [4] (h) Suggest a simple chemical test to distinguish the following two compounds.

X: CH3CH2CH2CONH2 and Y: CH3CH2CH2COO

NH4+

[2] [Total: 20]

END OF PAPER

27


RAFFLES INSTITUTION 2013 Year 6 Term 3 Common Test

H2 Chemistry

COVER SHEET

Name: ( )

CT Group:

For Examiners Use Only

Section

Marks

C1a b / 17

C1c / 3

C2 / 20

Penalty

Incorrect number of significant figures.

Missing OR wrong units.

Answers written in pencil.

Did not start question in Section C on a fresh page.

C

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2013 Y6 H2 Chem QP