Question

generally zinc oxide exists in white colour but sometimes it appears yellow colour why give equation

Answer 1

When zinc carbonate which is of white colour is heated, it decomposes to form zinc oxide and carbon dioxide gas. Experimentally, it is seen that when zinc carbonate is heated it first changes it's colour from white to yellow. This yellow coloured product is zinc oxide. Now, when it is allowed to cool down for sometime, it changes to white colour which is also zinc oxide. So, when hot, it appears yellow and when cool, it appears white.
Equations:-
ZnCO3 -------Heat-------› ZnO (yellow) + CO2.
ZnO (yellow) ------Cool-------› ZnO (White).

Thanks.

Answer 2

when zinc carbonate is heated it decomposes into zinc oxide and carbon dioxide
when it is obtained the color of the compound is yellow but when it is allowed to cool down it obtains white colour