Alkali Metals: Sodium and Its Compounds

Sodium Hydroxide (NaOH):

Manufacture of NaOH by Diaphragm cell:

A diaphragm cell is an electrolytic cell that consists of a steel tank with two compartments separated by a diaphragm of asbestos or metal oxide with a polymer. Graphite or titanium rod acts as an anode. Steel mesh acts as a cathode.

Sodium hydroxide can be manufactured by electrolysis of saturated brine solution using diaphragm cell.

NaCl(aq) ⇌ Na⁺ + Cl^–
H2O ⇌ H⁺ + OH^–

At anode: 2Cl^– → Cl₂ + 2e^–
At cathode: 2H⁺ + 2e^– → H₂

Na⁺ and OH^– ions present in solution combine with each other to form NaOH.
When saturated brine solution is passed through anode compartment, chlorine gas is collected at the anode, and hydrogen gas is collected at the cathode.
Na⁺ ions present in the anode compartment pass into the cathode compartment where Na⁺ ions combine with OH^– ion to form an aqueous solution of NaOH. This solution is subjected to crystallization to get solid NaOH.

Physical properties of NaOH:

1. NaOH is white, crystalline, deliquescent solid.
2. It is highly soluble in water and alcohol.
3. It is soapy to touch and bitter in taste.
4. It has a corrosive action on animal and vegetable tissue.

Chemical properties:

1. Action with carbon monoxide:

NaOH + CO → HCOONa(sodium formate)

2. Precipitations reactions:

CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄
FeSO₄ + 2NaOH → Fe(OH)₂ + Na₂SO₄
FeCl₃ + 3NaOH → Fe(OH)₃ + 3NaCl
ZnSO₄ + 2NaOH → Zn(OH)₂ + Na₂SO₄
Zn(OH)₂ + 2NaOH → Na₂ZnO₂ + H₂O
AlCl₃ + 3NaOH → Al(OH)₃ + 3NaCl

Uses of NaOH:

• Manufacture of paper, soap, cellulose, etc.
• Purifying oil.
• Extraction of aluminium metal.
• As lab reagent.