question_answer

Why does zinc oxide which is white in colour become yellow upon heating?

Answer:

                Zinc oxide (ZnO) crystals upon heating decompose as follows: \[ZnO\,Z{{n}^{2+}}(s)+1/2\,{{O}_{2}}(g)+2{{e}^{-}}\] The excess of \[Z{{n}^{2+}}\] ions formed are trapped in the interstitial spaces and the electrons are also trapped in the neighbourhood. These electrons absorb radiations corresponding to certain specific colour from the light and emit yellow light.