Question

How will you obtain the following? (Write chemical equations)

Washing Soda from Baking Soda
Plaster of Paris from Gypsum

Hint:

- Washing soda is used in detergent preparations and softening of water. - Plaster of Paris is used in making molds and casts.

Answer 1

1) Washing Soda from Baking Soda

Step 1: Thermal decomposition of baking soda (sodium hydrogen carbonate)
\[ \mathrm{2\,NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + CO_2 + H_2O} \] (Soda ash, \(\mathrm{Na_2CO_3}\), is formed.)

Step 2: Hydration to washing soda (decahydrate)
\[ \mathrm{Na_2CO_3 + 10\,H_2O \longrightarrow Na_2CO_3\cdot 10H_2O} \] (Washing soda crystals.)

2) Plaster of Paris from Gypsum

Controlled heating (about \(373\,\text{K}\)) of gypsum
\[ \mathrm{CaSO_4\cdot 2H_2O \xrightarrow{373\,K} CaSO_4\cdot \tfrac{1}{2}H_2O + \tfrac{3}{2}H_2O} \] \(\mathrm{CaSO_4\cdot \tfrac{1}{2}H_2O}\) is
Plaster of Paris (POP).