DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ1.3e

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.3.hl.TZ1.3e
Level hl Paper 3 Time zone TZ1
Command term Determine Question number e Adapted from N/A
e.
[Maximum mark: 3]
19M.3.hl.TZ1.3e

Lithium has many uses.

(e)

Lithium forms a crystalline lattice with the unit cell structure shown below.

X-ray diffraction shows that the length of the edge of the unit cell is 3.51 × 10−8 cm.

Determine the density of lithium, in g cm−3, using sections 2 and 6 of the data booklet.

[3]

Markscheme

mass of Li in unit cell = «  2 × 6.94  g mo l − 1 6.02 × 10 23  mo l − 1 » 2.31 × 10–23 g    [✔]

volume of unit cell = «(3.51 × 10–8 cm)3 =» 4.32 × 10–23 cm3    [✔]

«density =  2.31 × 10 − 23  g 4.32 × 10 − 23  c m 3 =» 0.535 «g cm–3»    [✔]

 

Note: Award [3] for correct final answer.

Examiners report

Most candidates had difficulty determining the number of atoms in lithium in a unit cell, even with a diagram provided. However, ECF marks were frequently scored.

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