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.
(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.
(iii) Sodium peroxide
First, is electrolysed to result in the formation of Na metal (Downs process). This sodium metal is then heated on aluminium trays in air to form its peroxide.
(iv) Sodium carbonate is prepared by Solvay process. Sodium hydrogen carbonate is precipitated in a reaction of sodium chloride and ammonium hydrogen carbonate.
These sodium hydrogen carbonate crystals are, heated to give sodium carbonate.
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 and .
(ii) Quick lime combines with silica to form slag.
(iii) When chloride is added to slaked lime, it gives bleaching powder.
(iv) calcium nitrate, on heating, decomposes to give calcium oxide.
Q: 18. Describe two important uses of each of the following:
(i) Caustic soda
(ii) Sodium carbonate
(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