Question

From the list of formulae given below, choose one, in each case corresponding to the salt having the given description:

$\mathrm{AgCl},{\mathrm{CuCO}}_3,{\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O},{\mathrm{ZnCO}}_3,{\mathrm{PbCl}}_2,\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2,\mathrm{NaCl},{\mathrm{KNO}}_3,{\mathrm{FeCl}}_2$

On heating this salt changes from green to black.

Answer 1

Copper carbonate is a green-colored salt that when heated decomposes to form Copper oxide along with Carbon dioxide.

$$\begin{gathered} {\mathrm{CuCO}}_3\left(\mathrm{s}\right)\to \mathrm{CuO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right) \\ (\mathrm{Copper}\mathrm{carbonate})(\mathrm{Copper}\mathrm{oxide})(\mathrm{Carbon}\mathrm{dioxide}) \end{gathered}$$

Copper oxide is black.

Hence, the answer is ${\mathrm{CuCO}}_3$