A Level Chemistry Exam Paper 4 - May-June 2023, Exams of Chemistry

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Chemistry - 9701 - 41 Paper 4 - A Level Structured

Questions Question Paper - May - June 2023 AS and A

Level - Cambridge International Examination

Cambridge International AS & A Level

CHEMISTRY 9701/

Paper 4 A Level Structured Questions May/June 2023

2 hours

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS

● Answer all questions.

● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.

● Write your name, centre number and candidate number in the boxes at the top of the page.

● Write your answer to each question in the space provided.

● Do not use an erasable pen or correction fluid.

● Do not write on any bar codes.

● You may use a calculator.

● You should show all your working and use appropriate units.

INFORMATION

● The total mark for this paper is 100.

● The number of marks for each question or part question is shown in brackets [ ].

● The Periodic Table is printed in the question paper.

● Important values, constants and standards are printed in the question paper.

This document has 28 pages. Any blank pages are indicated.

DC (EF/CT)

311840/

© UCLES 2023

[Turn over

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solution

1 (a) Group 2 nitrates decompose when heated.

Describe how the thermal stability of Group 2 nitrates changes with increasing

proton number. Explain your answer.

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

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........... [3]

(b) Copper(II) nitrate decomposes in a similar manner to Group 2

nitrates. Write an equation for the decomposition of

Cu(NO 3

)

2

.

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

........... [1]

(c) Cu(NO

3

)

2

is added to water to form

solution A. Fig. 1.1 shows some

reactions of solution A.

H

2

O

NH

3

(aq)

excess

NH

3

(aq

)

excess

concentrated

HC l

Fig. 1.

Complete Table 1.1 to show the formula and colour of each of the

copper-containing species present in A , B , C and D.

Table 1.

formula of

copper-containing

species formed

colour of

copper-containing

species formed

A

precipitat

solution solution Cu(NO 3

)

2

(

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B

C

D

[4]

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(d) EDTA

4– is a polydentate ligand.

(i) Explain what is meant by a polydentate ligand.

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

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

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

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

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

.......... [2]

(ii) Group 2 metal ions can form complexes similar to those of transition

elements.

A solution of EDTA

4– is added to water containing [Ca(H 2

O)

6

]

2+ to form a new

complex, [CaEDTA]

2– , as shown.

equilibrium 1 [Ca(H 2

O)

6

]

2+

• EDTA

4– [CaEDTA]

2–

• 6H 2

O

Circle on the structure of EDTA

4– in Fig. 1.2 the six atoms that form bonds with

the metal ion.

EDTA

4–

O O

• O CCH 2

O CCH 2

NCH

2

CH

2

N

CH

2

C O

CH

2

C O

O O

Fig. 1.

(iii) The calcium ions in [Ca(H 2

O)

6

]

2+ and [CaEDTA]

2– have a coordination

number of 6. Explain what is meant by coordination number.

[1]

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.......... [1]

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(iv) The complex [CaEDTA]

2– can be used to remove toxic metals from the body.

Table 1.2 shows the numerical values for the stability constants, K stab

, for

some metal ions with EDTA

4– .

Table 1.

complex K

stab

[CaEDTA]

2– 5.0 × 10

10

[CrEDTA]

• 2.5 × 10

23

[FeEDTA]

1.3 × 10

25

[PbEDTA]

2–

1.1 × 10

18

An aqueous solution containing [CaEDTA]

2–

is added to a solution containing

equal concentrations of Cr

3 +

(aq), Fe

3 +

(aq) and Pb

2 +

(aq). The resulting

mixture is left to reach a state of equilibrium.

State the type of reaction when [CaEDTA]

2 – reacts with Cr

3 + (aq), Fe

3 + (aq) and

Pb

2 +

(aq).

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

.......... [1]

(v) Deduce the relative concentrations of [CrEDTA]

• , [FeEDTA] - and [PbEDTA]

2–

present in the resulting mixture.

Explain your answer.

.......................................... > ..........................................

> ..........................................

highest concentration lowest concentration

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

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......... [1]

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(e) The number of moles of water of crystallisation in a hydrated ionic salt can be

determined by titration using aqueous EDTA

4– ions with a suitable indicator.

• 0.255 g of hydrated chromium(III) sulfate, Cr 2

(SO

4

)

3

• n H 2

O, is dissolved in

water and made up to 100 cm

3 in a volumetric flask.

• 25.0 cm

3 of this solution requires 26.2 cm

3 of 0.00800 mol dm

• aqueous

EDTA

4– ions to reach the end-point.

The reaction occurs as shown.

[Cr(H 2

O)

6

]

3 +

• EDTA

4 –

[CrEDTA]

• 6H 2

O

Use the data to calculate the value of n in the formula of

Cr 2

(SO

4

)

3

• n H 2

O. Show your working.

n =....................................................[3]

(f) A solution of Cr

3 +

(aq) and a solution of Fe

3 +

(aq) have different colours.

Explain why the two complexes have different colours.

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........... [2]

[Total: 19]

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BLANK PAGE

Cr Cr

Cr Cr

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2 (a) Some transition element complexes can show stereoisomerism.

State two types of stereoisomerism shown by transition element complexes.

1 ...............................................................................................................................

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

2 ................................................................................................................................................

[1]

(b) The complexes [Pt(NH 3

)

2

C l 2

] and [Pt( en ) 2

]

2+ have the same geometry (shape)

around the metal ion.

[Pt(NH 3

)

2

C l 2

] exists as two stereoisomers whereas [Pt( en ) 2

]

2+ only has one

possible structure. State the geometry around the metal ion.

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

........... [1]

(c) The complex [Cr( en ) 3

]

2 +

exists as two stereoisomers whereas the

complex [Cr(OCH 2

CH

2

NH

2

)

3

]

−

exists as four stereoisomers.

Complete the three-dimensional diagrams in Fig. 2.1 to show the four

stereoisomers of [Cr(OCH 2

CH

2

NH

2

)

3

]

−

.

Represent the ligand

• OCH

2

CH

2

NH

2

by using.

O N

Fig. 2.

[3]

intermediate

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(d) The complex [Cr(OCH 2

CH

2

NH

2

)

3

]

−

is formed by reacting Cr

2 +

(aq) with the

conjugate base of 2 - aminoethanol.

A synthesis of 2 - aminoethanol is shown in Fig. 2.2.

oxirane 2-aminoethanol

O

H C C

H

+

NH

3

OH

H

2

N

H H

Fig. 2.

(i) Suggest the mechanism for step 1 of the reaction of oxirane with ammonia in

Fig. 2.3.

Include all relevant curly arrows, lone pairs of electrons, charges and

partial charges. Draw the structure of the organic intermediate.

oxirane 2-aminoethanol

O

H C C

H

step

step

OH

H

2

N

H H

H

3

N

Fig. 2.

[3]

(ii) A small amount of by-product E , shown in Fig. 2.4, is produced during the

reaction shown in Fig. 2.2.

E

HO OH

N

H

Fig. 2.

Suggest how the formation of by-product E can be minimised.

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.......... [1]

F

0

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(iii) Compound F , C 4

H

9

NO, can be formed from the reaction of by-product E ,

C

4

H

11

NO

2

, with concentrated H 2

SO

4

.

Compound F is a saturated and basic organic compound.

Suggest a structure for compound F. State the type of reaction undergone by

E to form F.

type of reaction

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

[2]

[Total: 11]

[

]

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3

3 2 2

3

3

3

3 (a) Aqueous acidified iodate(V) ions, IO

, react with iodide ions, as shown.

IO

• • 6H

• 5 I

• 3 I + 3H O

The initial rate of this reaction is investigated. Table 3.1 shows the results

obtained.

Table 3.

experime

nt

• –

[IO

3

] / mol dm [H

] / mol dm

3

[I

• ] / mol

dm

initial rate / mol dm

3 min

1 0.0400 0.0150 0.0250 4.20 × 10

2 0.120 to be

calculated

0.0125 7.09 × 10

The rate equation for this reaction is rate = k [IO

• ][H

]

2 [I

• ]

2 .

(i) Explain what is meant by order of reaction.

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

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

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

.......... [1]

(ii) Complete Table 3.2.

Table 3.

the order of reaction with respect to

[IO

3

]

the order of reaction with respect

to [H

]

the order of reaction with respect

to [I

• ]

the overall order of reaction

[1]

(iii) Use your answer to (a)(ii) to sketch lines in Fig. 3.1 to show the relationship

between the initial rates and the concentrations of [IO

• ] and [I - ].

initial rate

0

[IO

0 ]

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initial rate

0

[I

• ]

Fig. 3.

0

3

[

]

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(iv) Use data from Table 3.1 to calculate the rate constant, k , for this reaction.

Include the units of k.

k = .............................. units......................[2]

(v) Use data from Table 3.1 to calculate the concentration of hydrogen ions,

[H

], in experiment 2.

[H

] = .............................. mol dm

3 [1]

(vi) This reaction is repeated in two separate experiments.

The experiments are carried out at the same temperature and with the

same concentrations of I

• and IO - .

One experiment takes place at pH 1.0 and the other experiment takes

place at pH 2.0. Calculate the value of

rate at pH 1. 0

.

rate at pH 2.

value of

rate at pH 1.

rate at pH 2.

= ..............................

[1]

(b) In aqueous solution, iron(III) ions react with iodide ions, as shown.

2Fe

3+

• 2 I

2Fe

2+

• I 2

The initial rate of reaction is first order with respect to Fe

3+ and second order

with respect to I

.

The mechanism for this reaction has three

steps. Each step involves only two ions

reacting together.

Suggest equations for the three steps of this mechanism. Identify the

rate-determining step. step 1

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........

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step 2

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

......

step 3

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

......

rate-determining step

= .............................

[3]

[Total: 10]

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4 (a) State the hybridisation of the carbon atoms and the C–C–H bond angle in

benzene, C 6

H

6

. Explain how orbital overlap leads to the formation of σ and π

bonds in benzene.

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........... [3]

(b) Compound Z can be synthesised from benzene in three steps by the route shown

in Fig. 4.1.

benzene Z

NH

2

step 1 step 3

step 2

Fig. 4.

(i) Draw structures for X and Y in Fig. 4.1. [2]

(ii) Give the reagents and conditions for steps 1, 2 and 3.

X Y

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step 1

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

.....

step 2

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

.....

step 3

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

.....

[3]

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(c) Compound W is an isomer of Z.

W

NH

2

Fig. 4.

Give the systematic name of W.

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

........... [1]

(d) Complete Table 4.1 to show the number of peaks observed in the carbon- 13 NMR

spectrum for W and Z.

Table 4.

compoun

d

number of peaks

observed

W

Z

[1]

[Total: 10]

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5 (a) The exhaust systems of most modern gasoline-fuelled cars contain a catalytic

converter with three metal catalysts.

These metals act as heterogeneous catalysts.

(i) Name three metal catalysts used in catalytic converters.

1 ................................. 2 ................................. 3 .................................

[1]

(ii) Explain what is meant by a heterogeneous catalyst.

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

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

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

.......... [1]

(b) The exhaust systems of many diesel-fuelled cars contain an additional system

to reduce vehicle emissions. This uses a liquid that is added to the exhaust

system.

This liquid contains urea, (NH 2

)

2

CO, which decomposes on heating to isocyanic

acid, HNCO, and ammonia.

reaction 1 (NH 2

)

2

CO HNCO + NH

3

Isocyanic acid reacts with water vapour to form ammonia and

carbon dioxide. reaction 2 HNCO(g) + H 2

O(g)

NH

3

(g) + CO 2

(g)

Some values for standard enthalpy changes of formation, Δ H f

o

, and standard

entropies, S

o

,

are given in Table 5.1.

Table 5.

compound Δ H f

o / kJ mol

• S

o / J K

mol

HNCO(g) –101.7 +238.

H

2

O(g) –241.8 +188.

NH

3

(g) –45.9 +192.

CO

2

(g) –393.5 +213.

(i) Explain what is meant by the term entropy of a system.

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

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.......... [1]

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(ii) Use the data in Table 5.1 to calculate Δ G

o for reaction 2 at

25 °C. Show your working.

Δ G

o = .............................. kJ mol

–1 [4]

(c) The ammonia formed in reactions 1 and 2 can be used to remove nitrogen

dioxide from exhaust emissions, as shown.

reaction 3 8NH 3

+ 6NO

2

7N

2

+ 12H

2

O

Use the equations for reactions 1, 2 and 3 to construct an overall equation for the

reduction of NO 2

by (NH 2

)

2

CO.

............................................................................................................................................. [1]

(d) Isocyanic acid, HNCO, can form cyanuric acid, C

3

H

3

N

3

O

3

, under certain conditions.

C

3

H

3

N

3

O

3

has a cyclic structure containing alternating carbon and nitrogen atoms

in the ring system.

Suggest a structure for cyanuric acid.

[1]

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(e) Isocyanic acid, HNCO, is a weak acid.

HNCO + H

2

O H

3

O

• NCO

p K a

= 3.70 at 25

°C

(i) Write the mathematical expressions for p K a

and pH.

p K a

=

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

......

pH =

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

........

[1]

(ii) Calculate the pH of 0.120 mol dm

–3

HNCO(aq). Give your answer to three

significant figures.

pH =...........................[2]

(iii) Calculate the percentage of HNCO molecules that are ionised in 0.120 mol

dm

–3 HNCO.

percentage ionisation of HNCO =......................[1]

[Total: 13]

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BLANK PAGE

O

N

H

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6 (a) Compound H has the structural formula CH 2

=CHCH(NH

2

)COOH.

(i) Name all the functional groups in H.

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

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

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

.......... [2]

(ii) Compound H exhibits stereoisomerism.

Draw three-dimensional structures for the two stereoisomers

of H. Name this type of stereoisomerism.

type of stereoisomerism

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

[2]

(b) Compound H can be prepared from the reaction of J with an excess of hot

aqueous acid.

J

O

O

Fig. 6.1

(i) Complete Fig. 6.2 to show the equation for this

reaction. O

O

+ CH =CHCH(NH )COOH +

2 2

N

H

O

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Fig. 6.2

[1]