question_answer 28)

Name the processes from which chlorine is obtained as the by- product. What will happen if an aqueous solution of NaCl is subjected to electrolysis?

Answer:

Chlorine is obtained as the bye-product in the following processes: (i) Manufacture of sodium by Down's process. (ii) Manufacture of sodium hydroxide or caustic soda in Nelson's cell. In Down's process, molten sodium chloride is subjected to electrolysis. During electrolysis, sodium is obtained at cathode while Cl2 is obtained at anode as a by product. NaCI(l)   Na+ + Cl? At cathode: Na+ + e? Na At anode:            Cl?Cl + e? 2CI Cl2 If however, an aqueous solution of NaCI is subjected to electrolysis, H2 is evolved at the cathode white Cl2 is obtained at the anode. This is because H+ ions are discharged in preference to Na+ ions since their discharge potential is less. Na+ and OH? remain in the solution. NaCl Na+ (aq) + CI? (aq) H­2O  H+ (aq) + OH?(aq) At cathode. H+ + e? H; H + H H2(g) At anode. Cl?Cl + e?; CI + ClCl2(g)