Reactions of the halogens

2 marks · Easy

A student adds chlorine to a solution containing sodium bromide. The student starts with 0.100 mol of sodium bromide. After the reaction, all the bromide ions have reacted. Calculate the maximum number of moles of bromine that could be formed, and explain your reasoning.

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0.050 mol of bromine is formed (because 2 moles of bromide ions produce 1 mole of bromine, so 0.100 mol / 2 = 0.050 mol).

Also accept: 0.05 mol; 0.050 moles of Br2; 0.05 mole

Common mistakes: Not dividing by two; Forgetting halogens form diatomic molecules

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Marking points

M1 · 1 mark · Correctly sets up the stoichiometry: 2 Br⁻ → Br₂.

A1 · 1 mark · Calculates that 0.050 mol of Br₂ is formed from 0.100 mol Br⁻.

Worked solution

The equation for the displacement reaction is:

2 moles of Br⁻ are needed to make 1 mole of Br₂. The student starts with 0.100 mol Br⁻ (from NaBr).

So: Number of moles of Br₂ formed = 0.100 mol / 2 = 0.050 mol.