Brine is electrolysed by using inert electrodes. The reaction at anode is_______

Options

A. `Cl_((aq))^(-) rarr (1)/(2) Cl_(2)(g) + e^(-), " "E_("Cell")^(Ө) = 1.36 V`
B. `2H_(2)O + (l) rarr O_(2)(g) + 4H^(+) + 4e^(-) : " "E_("Cell")^(Ө) = 1.23V`
C. `Na_((aq))^(+) + e^(-) rarr Na(s), " " E_("Cell")^(Ө)= 2.71 V`
D. `H_((aq))^(+) + e^(-) rarr (1)/(2) H_(2)(g), " "E_("Cell")^(Ө)= 0.00 V`

Answer

A

Explanation

Brine is electrolysed by using inert electrodes. The possible reactions occurring at anode are
`Cl_((aq))^(-) rarr (1)/(2) Cl_(2)(g) + e^(-), " "E_("Cell")^(Ө) = 1.36 V`
`2H_(2)O + (l) rarr O_(2)(g) + 4H^(+) + 4e^(-) : " "E_("Cell")^(Ө) = 1.23V`
The reaction at anode with lower value of `E^@` is preferred and therefore water should get oxidised in preference to `Cl^(-)(aq)`. However, `Cl_2` is produced instead of `O_2`. This unexpected result is explained on the basis of the fact that water needs greater voltage for oxidation to `O_2` (as it is kinetically slow process) than that needed for oxidation of `Cl^-` ions to `Cl_2`