The electrolysis of aqueous solutions

3 marks · Normal

When electrolysing concentrated sodium chloride solution, a student expected to collect 10 cm³ of gas at each electrode. However, only 6 cm³ of chlorine gas was collected at the anode. Calculate the percentage of chlorine gas lost, and explain a possible reason for this observation.

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40% (±1)

(a) 40%

(b) Because chlorine is soluble in water

Also accept: Chlorine is lost because it dissolves in water

Common mistakes: Incorrect calculation for percentage loss

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Marking points

M1 · 1 mark · Correctly determines volume of chlorine lost (10 - 6 = 4 cm³)

M2 · 1 mark · Uses correct calculation: (4/10) × 100 (follow-through)

A1 · 1 mark · Arrives at final answer: 40% and explanation that chlorine dissolves in water (follow-through)

Worked solution

Expected chlorine gas = 10 cm³; actual collected = 6 cm³; lost = 10 - 6 = 4 cm³.

Chlorine is lost because it is soluble in water, so not all the chlorine gas is collected.