CAIE A-Level Chemistry 11.3.1 Halide Ions as Reducing Agents

Practise ranking chloride, bromide and iodide reducing strength and using it to explain redox outcomes.

Exam points

state that reducing strength increases from Cl− to Br− to I− down Group 17
identify oxidation of a halide ion by its electron loss and formation of the corresponding halogen
explain why chloride gives the highest HX yield with concentrated H2SO4 while bromide and iodide reduce it

[Maximum number: 2]

The chlorides of some of the Period 3 elements are shown in Table 2.1.

Table 2.1

An excess of $\mathrm{Cl}^{-}(\mathrm{aq})$ is added to $1 \mathrm{~cm}^{3}$ of $\mathrm{Br}_{2}(\mathrm{aq})$ .

Describe what is observed. Explain your answer.

M1 orange colour (of solution) remains / no visible reaction

M2

bromine $/ \mathrm{Br}_{2}$ cannot oxidise chloride/Ct

OR

bromine $/ \mathrm{Br}_{2}$ is not a strong enough oxidising agent (to oxidise chloride/Cl-)

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11.3.1—Reactivity of halide ions as reducing agents question 1