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 :
(a) potassium dichromate solution and sulphur dioxide

(b) potassium permanganate solution and sulphur dioxide

(c) potassium permanganate solution and lemon juice

(d) potassium dichromate solution and carbon dioxide.

Answer 1

(a) potassium dichromate solution and sulphur dioxide

Sulphur dioxide gas changes acidifed Potassium Dichromate solution from orange to green.

Chemical reaction:

Sulphur dioxide reacts with acidified potassium Dichromate solution to give Chromium Sulphate , Poatssium sulphate and water.

$3S{O}_2\left(g\right)+K_{2}C{r}_2{O}_7\left(aq\right)+H_{2}S{O}_4\left(aq\right)⟶C{r}_2\left(S{O}_4{)}_3\right(aq)+K_{2}S{O}_4(aq)+H_{2}O(l)$