AS & A Level CHEMISTRY9701/41 Paper 4 A Level Structured Questions May/June 2023 Authentic Marking Scheme

Cambridge International AS & A Level
* 2 5 6 3 6 1 9 2 8 2 *




CHEMISTRY 9701/41
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) 311840/6
© UCLES 2023 [Turn over

, 2

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

Write an equation for the decomposition of Cu(NO3)2.

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(c) Cu(NO3)2 is added to water to form solution A.
Fig. 1.1 shows some reactions of solution A.

H 2O
Cu(NO3)2(s) solution A solution C
excess
NH3(aq)
NH3(aq)

precipitate B excess
concentrated HCl

solution D

Fig. 1.1

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 1.1

formula of copper‑containing colour of copper‑containing
species formed species formed
A
B
C
D
[4]




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, 3

(d) EDTA4– is a polydentate ligand.

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

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

A solution of EDTA4– is added to water containing [Ca(H2O)6]2+ to form a new complex,
[CaEDTA]2–, as shown.

equilibrium 1 [Ca(H2O)6]2+ + EDTA4– [CaEDTA]2– + 6H2O

Circle on the structure of EDTA4– in Fig. 1.2 the six atoms that form bonds with the metal
ion.

EDTA4–
O O

–O CCH2 CH2C O–
NCH2CH2N
–O CCH2 CH2C O–

O O

Fig. 1.2
[1]

(iii) The calcium ions in [Ca(H2O)6]2+ and [CaEDTA]2– have a coordination number of 6.

Explain what is meant by coordination number.

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, 4

(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, Kstab, for some metal
ions with EDTA4–.

Table 1.2

complex Kstab

[CaEDTA]2– 5.0 × 1010
[CrEDTA] – 2.5 × 1023
[FeEDTA] – 1.3 × 1025
[PbEDTA]2– 1.1 × 1018


An aqueous solution containing [CaEDTA]2– is added to a solution containing equal
concentrations of Cr 3+(aq), Fe3+(aq) and Pb2+(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), Fe3+(aq) and Pb2+(aq).

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(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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© UCLES 2023 9701/41/M/J/23