Explain the following giving reason:
a) Electrolysis of aqueous solution of sodium and calcium salts give H2 gas at the cathode where as that of copper and silver salts gives these metals at the cathode.
b) An aqueous solution of bromide or iodide gives Br2 or I2 at the anode whereas electrolysis of aqueous solution of fluoride does not give F2 gas at the anode.
a) According to electrochemical series, hydrogen is considered as standard and metals which are more reactive than hydrogen are placed at the top and metals which are less reactive than hydrogen are placed at the bottom. When electrolysis of metal salts which are more reactive than hydrogen are done, hydrogen is liberated at the cathode and metal salts less reactive than hydrogen are done then the metal is deposited at the cathode. Na and Ca are at the top and copper and silver are at the bottom
NaCl + H2O -----> Na+OH- + H2 + 1/2 Cl2
b) Due to overvoltage, reduction potential of water is higher than that of halogen, so halogens are released at anode. But the reduction potential of F– is the highest, oxidation of fluoride ions is not possible. So an aqueous solution of bromide or iodide gives Br2 or I2 at the anode whereas electrolysis of aqueous solution of fluoride does not give F2
NaCl + H2O -----> Na+OH- + H2 + 1/2 Cl2
b) Due to overvoltage, reduction potential of water is higher than that of halogen, so halogens are released at anode. But the reduction potential of F– is the highest, oxidation of fluoride ions is not possible. So an aqueous solution of bromide or iodide gives Br2 or I2 at the anode whereas electrolysis of aqueous solution of fluoride does not give F2