Question

Name a salt blue in color but becomes white upon strong heating.

Answer 1

1. Hydrated Copper sulphate (CuSO₄.5H₂O) also called blue vitriol, is a blue-colored salt that turns white upon strong heating as it loses its water of crystallization.
2. The color of anhydrous copper sulphate is white in color that turns blue when it is in hydrated form.
3. When this blue copper sulphate is heated it again converts into anhydrous form and the color is changed.

The reaction is given as:-

${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\left(\mathrm{blue}\right)\stackrel{\mathrm{Heat}}{\to }{\mathrm{CuSO}}_4\left(\mathrm{s}\right)\left(\mathrm{White}\right)+5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$

Hence, Hydrated Copper sulphate is a salt blue in color but becomes white upon strong heating.