JAMB Chemistry 2021 Paper

Concept:A breathalyzer detects alcohol in exhaled air using a chemical reaction that changes colour.Explanation:The exhaled alcohol is oxidised by acidified potassium dichromate. The reagent is a mixture of potassium dichromate and sulphuric acid. In this reaction, orange dichromate ions are reduced to green chromium(III) ions. The colour change confirms the presence of alcohol. The reaction is: $3\mathrm{C}_2\mathrm{H}_5\mathrm{OH} + 2\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7 + 8\mathrm{H}_2\mathrm{SO}_4 \rightarrow$ green product.Thus, the breath test reagent is potassium dichromate acidified with sulphuric acid.Answer:D. Potassium dichromatic-sulphuric acid.