redox reaction

Sodium sulphite is a reducing agent, while acidifiedpotassium dichromate is an oxidizing agent. When they are mixed, redox reaction occurs.

In the redox reaction, the colourless sulphite ions in sodium sulphite areoxidized to colourless sulphate ions, while the orange dichromate ions in acidifiedpotassium dichromate solution are reduced to green chromium(III) ions.

The observation is that the orange acidified potassium dichromate solution ischanged to green.

The two half ionic equations are :
SO3^2-(aq) + H2O(l) → SO4^2-(aq) + 2H^+(aq) + 2e^- ...... (1)
Cr2O7^2-(aq) + 14H^+(aq) + 6e^- → 2Cr^3+(aq) + 7H2O(l) ...... (2)

(1)´3 + (2), the overall ionic equation is
3SO3^2-(aq) + Cr2O7^2-(aq)+ 8H^+(aq) → 3SO4^2-(aq) + 2Cr^3+(aq)+ 4H2O(l)