Question

Name a carbonate which gives yellow residue on heating but the residue turns white on cooling.

Answer 1

Zinc Carbonate (${\mathrm{ZnCO}}_3$) is a white amorphous solid which on heating gives CO₂ and yellow colour residue i.e. Zinc Oxide ($\mathrm{ZnO}$).

Reaction: -

${\mathrm{ZnCO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{ZnO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

$\mathrm{ZnO}$ (Zinc oxide) is a yellow colour residue which turns white on cooling.