Ncert Exercises & Solutions

Why does white ZnO (s) becomes yellow upon heating?

On heating ZnO loses oxygen as follows

ZnO \overset{Heat}{⟶} {Zn}^{2 +} + \frac{1}{2} O_{2} + 2 e^{-}

Zn²⁺ ions and electrons move to interstitial sites and F-centres are formed which impart yellow colour to ZnO(s).