Chemistry Class 11 NCERT Solutions: Chapter 10 the s Block Elements Part 6

Q: 16. Starting with sodium chloride how would you proceed to prepare

(i) Sodium metal

(ii) Sodium hydroxide

(iii) Sodium peroxide

(iv) Sodium carbonate

Answer:

(A) Sodium can be extracted from sodium chloride by Downs process. This process involves the electrolysis of fused Equation and Equation at a temperature of 1123 K in Downs cell.

Steel is the cathode and a block of graphite acts as the anode. Metallic Na and Ca are formed at cathode. Molten sodium is taken out of the cell and collected over kerosene.

Equation

Molten

At Cathode: Equation

At Anode: Equation

Equation

(ii) Sodium hydroxide can be prepared by the electrolysis of sodium chloride. This is called Castner-Kellner process. In this process, the brine solution is electrolysed using a carbon anode and a mercury cathode. The sodium metal, which is discharged at cathode, combines with mercury to form an amalgam.

Equation

Equation

(iii) Sodium peroxide

First, Equation is electrolysed to result in the formation of Na metal (Downs process). This sodium metal is then heated on aluminium trays in air Equation to form its peroxide.

Equation

(iv) Sodium carbonate is prepared by Solvay process. Sodium hydrogen carbonate is precipitated in a reaction of sodium chloride and ammonium hydrogen carbonate.

Equation

Equation

Equation

These sodium hydrogen carbonate crystals are, heated to give sodium carbonate.

Equation

Q: 17. What happens when

(i) Magnesium is burnt in air

(ii) Quick lime is heated with silica

(iii) Chlorine reacts with slaked lime

(iv) Calcium nitrate is heated

(i) Magnesium burns in air with a dazzling light to form Equation and Equation .

Equation

Equation

(ii) Quick lime Equation combines with silica Equation to form slag.

Equation

(iii) When chloride is added to slaked lime, it gives bleaching powder.

Equation

(iv) calcium nitrate, on heating, decomposes to give calcium oxide.

Equation

Q: 18. Describe two important uses of each of the following:

(i) Caustic soda

(ii) Sodium carbonate

(iii) Quicklime

Answer:

(i) Uses of caustic soda

(A) It is used in soap industry

(B) It is used as a reagent in laboratory

(ii) Uses of sodium carbonate

(A) It is generally used in glass and soap industry.

(B) It is used as a water softener

(iii) Uses of quick lime

(A) It is used as a starting material for obtaining slaked lime

(B) It is used in the manufacture of glass and cement

Explore Solutions for Chemistry