Discuss the industrial production of sodium hydroxide ($NaOH$ - Caustic Soda) and mention its properties and uses.

(N/A) Sodium hydroxide is generally prepared commercially by the electrolysis of sodium chloride in a $Castner-Kellner$ cell. $A$ brine solution is electrolysed using a mercury cathode and a carbon anode. Sodium metal discharged at the cathode combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode.
Cathode: $Na^{+} + e^{-} \xrightarrow{Hg} Na-\text{amalgam}$
Anode: $Cl^{-} \rightarrow \frac{1}{2} Cl_{2} + e^{-}$
The amalgam is treated with water to give sodium hydroxide and hydrogen gas.
$2Na-\text{amalgam} + 2H_{2}O \rightarrow 2NaOH + 2Hg + H_{2}$
Properties: Sodium hydroxide is a white,translucent solid. It melts at $591 \ K$. It is readily soluble in water to give a strong alkaline solution. Crystals of sodium hydroxide are deliquescent.
The sodium hydroxide solution at the surface reacts with the $CO_{2}$ in the atmosphere to form $Na_{2}CO_{3}$.
Uses: $(i)$ The manufacture of soap,paper,artificial silk and a number of chemicals,$(ii)$ In petroleum refining,$(iii)$ In the purification of bauxite,$(iv)$ In the textile industries for mercerising cotton fabrics,$(v)$ For the preparation of pure fats and oils,and $(vi)$ As a laboratory reagent.