Question

With the help of an appropriate example, justify that some of the chemical reactions are determined by a change in colour.

Give a chemical equation for the reaction involved in the above case. 

Give one example of a chemical reaction characterised by a change in colour.

Answer 1

When sulphur dioxide gas is passed through an acidified potassium dichromate solution, the orange colour of the potassium dichromate solution changes to green colour.

\[\ce{3SO2_{(g)} + K2Cr2O7_{(aq)} + H2SO4_{(aq)} -> K2SO4_{(aq)} + Cr2(SO4)3_{(aq)} + H2O_{(l)}}\]