DP Chemistry (last assessment 2024)

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Question 23M.3.HL.TZ1.5

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Date May 2023 Marks available [Maximum mark: 9] Reference code 23M.3.HL.TZ1.5
Level HL Paper 3 Time zone TZ1
Command term Calculate, Determine, Identify, Show Question number 5 Adapted from N/A
5.
[Maximum mark: 9]
23M.3.HL.TZ1.5

Copper forms a face-centred cubic structure:

(a.i)

Identify the coordination number and number of atoms per unit cell for this structure.

 

Coordination number:

 

 

Number of atoms per unit cell:

 

 

 

[2]

Markscheme

Coordination number: 12 ✓
Number of atoms per unit cell: 4 ✓

(a.ii)

The edge length of a unit cell of copper is 3.61 × 10−8 cm. Determine the density of copper, in g cm−3, using your answer to part (a)(i) and sections 2 and 6 of the data booklet.

[3]

Markscheme

V= «(3.61 × 10−8 cm)3 =» 4.70 × 10−23 «cm3» ✓
Mass of unit cell = «63.55 g mol−1 × 4 ÷ 6.02 × 1023 » 4.22 × 10−22 « g » ✓
4.22 × 10−22 g ÷4.70 × 10−23 «cm3» 8.98 g cm−3 ✓

Award [3] for correct final answer.

(b)

The Ksp of copper (II) hydroxide is 2.2 × 10−20. Calculate the molar solubility of Cu2+ (aq) ions in a solution of pH 9.

[2]

Markscheme

Ksp =[Cu2+][OH−]2
OR
2.2 × 10−20 =[Cu2+] × (10−5)2 ✓

[Cu2+] «= Ksp/[OH−]2 =2.2 x 10−20/(10−5)2»
= 2.2 ×10−10«mol dm−3» ✓


Award [2] for correct final answer.

The Haber–Weiss reaction produces hydroxyl radicals.

H2O2 + •O2− → O2 + OH− + •OH

(c)

Show the two-step mechanism by which Cu2+ ions can catalyse this reaction by reacting with the superoxide ion, •O2−, in the first step.

[2]

Markscheme

Cu2+ + •O2− → Cu+ + O2 ✓
Cu+ + H2O2 → Cu2+ + OH− + •OH ✓