Question

When a blue coloured copper salt is heated strongly, it forms a white copper salt. The white copper salt can be reconverted into blue copper salt by adding a liquid X.
(a) Write the formula of blue copper salt.
(b) Write the formula of white copper salt.
(c) What substance is lost when blue copper salt is converted into white copper salt?
​(d) Name the liquid X.

Answer 1

(a) The formula for blue copper salt is CuSO₄.5H₂O.

(b) The formula for white copper salt is CuSO₄.

(c) Copper sulphate crystals are blue in colour, which on heating lose all the water of crystallization and become anhydrous.

${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}\to \underset{\mathrm{anhydrous}}{{\mathrm{CuSO}}_4}+5{\mathrm{H}}_2\mathrm{O}$

(d)When anhydrous copper sulphate gets few drops of water it becomes hydrous, and imparts blue colour to copper sulphate crystals.

$\underset{\mathrm{anhydrous}}{{\mathrm{CuSO}}_4}+5{\mathrm{H}}_2\mathrm{O}\to {\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}$

So, X must be water.