Question

'A' is a blue coloured crystalline salt. On heating, it loses blue colour and to give 'B'. When water is added, 'B' gives back to 'A'. Identify A and B, write the equation.

Answer 1

Since ‘A’ is a blue coloured crystalline salt, it is CuSO₄. 5H₂O (Blue vitriol). On heating, it loses all five water molecules and becomes colourless anhydrous CuSO₄.

\[\ce{\underset{\text{(A)}}{CuSO4.5H2O} ⇌[heating][cooling]\underset{\text{anhy. copper sulphate} Colourless (B)}{CuSO4 + 5H2O}}\]

When water is added ‘B’ gives back A.