127.

What difficulities arise in the extraction of sodium? How these difficulties are overcome?

Difficulties in the extraction of sodium: The sodium metal cannot be extracted by the usual procedure due to the following reasons:
1. Sodium is a very strong reducing agent and it cannot be obtained by the reduction of sodium oxide with a reducing agent such as carbon.
2. It cannot be prepared from its aqueous solution by metal displacement method as the liberated metal reacts with water.
3. The metal cannot be isolated by the electrolysis of the aqueous solution of its salt such as NaCl because the sodium formed at cathode at once reacts with water producing sodium hydroxide and liberates hydrogen gas.
The above difficulties are solved by carrying out the electrolysis of sodium chloride containing some calcium chloride and potassium fluoride also in the molten state.

Molten sodium chloride cannot be used due to the following reasons:
(i) The melting point of sodium chloride (1085K) is very high and it is quite difficult to keep the sodium chloride in the molten state at such a high temperature during its electrolysis.

(ii) Since the boiling point of sodium is 1160K, the metal tends to change into vapours at a high temperature of electrolysis.

(iii) At the high temperature of electrolysis, both liberated sodium and molten sodium chloride tend to form a fog which is very difficult to separate.

(iv) The product of electrolysis (sodium and chlorine) can react chemically with the apparatus used for electrolysis at high temperature.
The main function of calcium chloride and potassium fluoride is to lower the melting point of sodium chloride from 1085K to 873K. This is because the above-mentioned difficulties are only due to the high melting point of sodium chloride.