Question

Question 10.16 Starting with sodium chloride how would you proceed to prepare
(i) sodium metal

(ii) sodium hydroxide

(iii) sodium peroxide

(iv) sodium carbonate?

Class XI The s-Block Elements Page 306

Answer 1

(i) Sodium metal:- It is manufactured by electrolysis of a fused mixture of NaCl
(40%) and CaCl2 (60%) in Down's cell at 873 K. Na, liberated at the cathode is collected, in kerosene oil While Cl2 is evolved at the anode.

NaCl ------->Na+ + Cl- {electrolysis}
At cathode, Na+ + e---->Na
at anode, 2Cl- ---->Cl2 + 2e-

(ii)Sodium hydroxide: It is manufactured by electrolysis of an aqueous solutlon of NaCl (brine) in Castner-Kellner cell using mercury cathode and carbon anode. Sodium metal which is discharged at the cathode combines with mercury to form sodium amalgam, Cl2 gas is evolved at the anode.

at cathode, Na+ + e- ---> Na-amalgam
at anode, 2Cl- --->Cl2 + 2e-

The sodium amalgam thus obtained is treated with water to form sodium hydroxide and Hydrogen gas.
2Na-amalgam + 2H2O--->2NaOH + 2Hg + H2

(iii)Sodium peroxide:It is obtained by heating sodium metal (which is obtained by the electrolysis of molten NaCl), in excess of air. The intially formed sodium oxide reacts with more O2 to form Na2O2.

4Na + O2 ---> 2Na2O
2Na2O + O2 -->2Na2O2

(iv) sodium carbonate:- it is obtained with help of Solvay ammonia process. When CO2 is passed through a concentrated solution of brine (aqueous solution of NaCl) saturated with ammonia , NaHCO3 gets precipitated. NaHCO3 9n subsequent heating gives Na2CO3.

NaCl + NH3 + CO2 + H2O --->NaHCO3↓+ NH4Cl

2NaHCO3 -->Na2CO3 + CO2 + H2O

Answer 2

NaCl(molten)electrolysis -------------->Na+ + Cl-

1. while electrolysis of NaCl of molten state produce Na metal (above reaction )
2. when the Na react with amalgam and H2O it gives NaOH

2Na-amalgam + H2O ------> NaOH

3. from the first reaction

2Na + O2 --------> 2Na2O2

4.when NH4CO3, NaCl, NH4Cl react each

other produces the following reaction

NH4CO3+ NaCl+NH4Cl------>NaHCO3

NaHCO3 (on heating) ------> Na2CO3

hope this answer is useful for u