Acids, Bases and Salts - More About Salts: Family of Salt, Chemicals from Common Salt

Salts are formed by the neutralization reaction between an acid and a base. Salts of a strong acid and a strong base are neutral with $pH = 7$. Salts of a strong acid and a weak base are acidic with $pH < 7$. Salts of a strong base and a weak acid are basic with $pH > 7$.

Common salt ($NaCl$) is a vital raw material for various chemicals including Sodium Hydroxide, Bleaching Powder, Baking Soda, and Washing Soda.

The Chlor-alkali process involves the electrolysis of an aqueous solution of sodium chloride (brine). It produces sodium hydroxide ($NaOH$) at the cathode, chlorine gas ($Cl_2$) at the anode, and hydrogen gas ($H_2$) at the cathode.

Bleaching Powder ($CaOCl_2$) is produced by the action of chlorine on dry slaked lime ($Ca(OH)_2$). It is used for bleaching cotton and linen in the textile industry and as a disinfectant for water.

Baking Soda ($NaHCO_3$) is produced using the Solvay process: $NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3$. When heated during cooking, it decomposes: $2NaHCO_3 \xrightarrow{\text{Heat}} Na_2CO_3 + H_2O + CO_2$.

Washing Soda ($Na_2CO_3 \cdot 10H_2O$) is obtained by the recrystallization of sodium carbonate. It is a basic salt used in glass, soap, and paper industries and for removing permanent hardness of water.

Water of Crystallisation is the fixed number of water molecules present in one formula unit of a salt. For example, Copper Sulphate crystals contain 5 molecules of water ($CuSO_4 \cdot 5H_2O$).

Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$) is obtained by heating Gypsum ($CaSO_4 \cdot 2H_2O$) at $373 \text{ K}$. If mixed with water, it changes back to Gypsum, forming a hard solid mass.