Question

When blue copper sulphate crystals are heated, they become _______________ (white/black).

Answer 1

• In blue copper sulfate crystals (CuSO₄.5H₂O), water molecules are trapped in them (known as the water of crystallization).
• While heating, it undergoes dehydration due to loss of water.
• As a result, the color of the crystals changes from blue to white.

$\underset{(\mathrm{copper}\mathrm{sulfate}-\mathrm{hydrated})}{{\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}\stackrel{\mathrm{heat}}{\to }\underset{(\mathrm{copper}\mathrm{sulfate}-\mathrm{anhydrous})}{{\mathrm{CuSO}}_4\left(\mathrm{s}\right)}+\underset{\mathrm{water}}{5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)}$

Hence, when blue copper sulfate crystals are heated, they become white.