Question

The chemical reaction between two substances is characterised by a change in colour from orange to green. These two substances are most likely to be ______.

Options

• potassium dichromate solution and sulphur dioxide

• potassium permanganate solution and sulphur dioxide

• potassium permanganate solution and lemon juice

• potassium dichromate solution and carbon dioxide

Answer 1

The chemical reaction between two substances is characterised by a change in colour from orange to green. These two substances are most likely to be potassium dichromate solution and sulphur dioxide.

Explanation:

Potassium dichromate (K₂Cr₂O₇) is an oxidising agent that naturally forms a bright orange solution due to its dichromate ions. When sulphur dioxide (SO₂) gas is passed through it, a redox reaction occurs where the sulphur dioxide acts as a reducing agent. This reduces the chromium ions from an oxidation state of +6 (orange) to +3 (green), turning the entire solution green.