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Date May 2018 Marks available 1 Reference code 18M.3.hl.TZ1.5
Level HL Paper 3 Time zone TZ1
Command term Outline Question number 5 Adapted from N/A

Question

Aluminium is produced by the electrolysis of a molten electrolyte containing bauxite.

The graph of the resistance of aluminium with temperature is shown below.

M18/4/CHEMI/HP3/ENG/TZ1/05.d

The diagram illustrates the crystal structure of aluminium metal with the unit cell indicated. Outline the significance of the unit cell.

M18/4/CHEMI/HP3/ENG/TZ1/05.b

[1]
b.

When X-rays of wavelength 0.154 nm are directed at a crystal of aluminium, the first order diffraction pattern is observed at 18°. Determine the separation of layers of aluminium atoms in the crystal, in m, using section 1 of the data booklet.

[2]
c.

Deduce what the shape of the graph indicates about aluminium.

[2]
d.i.

Outline why the resistance of aluminium increases above 1.2 K.

[1]
d.ii.

The concentration of aluminium in drinking water can be reduced by precipitating aluminium hydroxide. Calculate the maximum concentration of aluminium ions in water of pH 7 at 298 K. Solubility product of aluminium hydroxide = 3.3 × 10−34 at 298 K.

[2]
e.

Markscheme

the smallest repeating unit «from which the crystal structure can be derived»

 

Accept “building block that the structure is made from”.

[1 mark]

b.

« = 2d sin θ»

1 × 1.54 × 10–10 = 2 × d × sin 18

d «\(\frac{{1.54 \times {{10}^{ - 10}}{\text{ m}}}}{{2 \times 0.309}}\)» = 2.49 × 10–10 «m»

 

Award [2] for correct final answer.

[2 marks]

c.

type 1

superconductor

[2 marks]

d.i.

collisions between electrons and «lattice of metal» ions become more frequent

OR

thermal oscillations/vibrations disrupt the Cooper electron pairs

[1 mark]

d.ii.

Ksp = [Al3+][OH]3 «= 3.3 × 10–34»

[Al3] = «\(\frac{{3.3 \times {{10}^{ - 34}}}}{{{{(1 \times {{10}^{ - 7}})}^3}}} = \)» 3.3 × 10–13 «mol dm–3»

 

Award [2] for correct final answer.

[2 marks]

e.

Examiners report

[N/A]
b.
[N/A]
c.
[N/A]
d.i.
[N/A]
d.ii.
[N/A]
e.

Syllabus sections

Options » A: Materials » A.8 Superconducting metals and X-ray crystallography (HL only)
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