Question

Starting with sodium chloride how would you proceed to prepare 

(i) sodium metal 

(ii) sodium hydroxide 

(iii) sodium peroxide 

(iv) sodium carbonate?

Answer 1

(i) sodium metal:Sodium chloride can be converted into sodium by Downs process. It can be achieved by electrolysis of fused CaCl₂ (60 %) and NaCl (40%) at 1123 K in a special apparatus (Downs cell).

A graphite block is the anode while steel is made the cathode. Metallic Ca and Na are formed at the cathode. Molten Na is supported by dipping in kerosene.

Nacl →Electrolysis Na⁺ + Cl^–

(Molten) At Cathode: 

Na⁺ +e^– → Na At Anode: 

Cl^– - e^– → Cl

(ii)Sodium Hydroxide: By electrolyzing a solution of sodium chloride, we can get Sodium hydroxide. This process is commonly known as Castner- Kellner process. The process is carried out using a mercury cathode and a carbon anode. Sodium metal, deposited at cathode forms an Amalgam by combining with Mercury.

Cathode: Na⁺ +e^– →Hg Na-Amalgam 

Anode; 2 Cl^– → Cl₂ + 2e^– 

Cl + Cl → Cl₂

(iii) Sodium peroxide: After Na metal is gotten from Downs process, it is heated on Aluminium trays in presence of air(without CO₂) to form Sodium peroxide.

2Na + O_2(air) → Na₂O₂

(iv) Sodium carbonate: Sodium hydrogen carbonate is obtained as a precipitate by reacting sodium chloride with ammonium hydrogen carbonate. The resultant crystals can be heated to obtain Sodium Carbonate.

2NH₂ + H₂O → (NH₄)₂CO₃

(NH₄)₂CO₃ + H₂O + CO₂ → 2NH₄HCO₃

2NH₄HCO₃ + NaCl → NH₄Cl + NaHCO₃

The resultant crystals can be heated to obtain Sodium Carbonate.

2NaHCO₃ → Na₂CO₃+ CO₂ + H₂O