CBSE Class 10 Science 2019 · Paper 31/1/1/C · Question 7(b)

Acids, Bases and Salts 3 marks Medium

(a)Why is electrolysis of brine called ‘Chlor-alkali process’ ? Write the chemical equation involved in this process.
(b)A few crystals of hydrated copper sulphate are heated in a dry test-tube. Enlist any two observations.

Answer

Brine electrolysis gives chlorine and an alkali, NaOH; heated hydrated copper sulphate turns white and gives water droplets.

(a) The electrolysis of brine gives chlorine ("chlor") and sodium hydroxide, an alkali ("alkali"), so it is called the chlor-alkali process:

2 NaCl (a q) + 2 H_{2} O (l) ⟶ 2 NaOH (a q) + Cl_{2} (g) + H_{2} (g)

(b) (i) The blue crystals turn white, as anhydrous copper sulphate forms. (ii) Droplets of water appear on the cooler inner walls of the test tube. (

CuSO_{4} \cdot 5 H_{2} O heat CuSO_{4} + 5 H_{2} O

)

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