Edexcel IAL Chemistry 8.7 Disproportionation reactions

Assign the element's initial value and both product values, demonstrate one increase and one decrease and balance the ionic equation if the question asks for it.

Exam points

Identify disproportionation by tracking one element to higher and lower oxidation states.
Justify chlorine or manganese disproportionation with all three oxidation numbers.
Balance an ionic disproportionation equation with atoms, charge and state symbols.

[Maximum number: 2]

Chlorine dioxide, $\mathrm{ClO}_{2}$ , can be used to treat water to make it safe for drinking. The molecule is a free radical. One suggested structure is shown.

Figure for Question 8.7—A disproportionation reaction involves an element in a single species being simultaneously oxidised and reduced question 1 — Edexcel A-Level Chemistry AS

Chlorine dioxide can be made from potassium chlorate(V), $\mathrm{KClO}_{3}$ , in a two-step process.

Step 1 Potassium chlorate(V) reacts with concentrated sulfuric acid to form compound A.

Step 2 Compound A then undergoes a disproportionation reaction to form chlorine dioxide and hydrogen chlorate(VII), $\mathrm{HClO}_{4}$ .

In Step 2, compound A undergoes disproportionation. Deduce the possible range of oxidation numbers for the chlorine in compound A. Justify your answer.

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8.7—A disproportionation reaction involves an element in a single species being simultaneously oxidised and reduced question 1