In the electrolysis of aqueous sodium chloride solution, which of the half cell reactions will occur at anode?

Options

A. `Na^(+) (aq) + e^(-) rarr Na(s) E^@ =-2.71` volts
B. `2H_2O(l) rarr O_2 + 4H^+ +4e^(-)E_("cell")^(@) = 1.23` volts
C. `H^(+)(aq) + e^(-) rarr (1)/(2) H_2 " " E_("cell")^@ = 0.00` volts
D. `Cl^(-)(aq) rarr 1/2 Cl_2 + e^(-)" "E_("cell")^(@)=1.36` volts

Answer

D

Explanation

During electrollysis of aqueous
`NaCl rarr Na^(+) Cl^(-)`
`H_2O rarr H^+ OH^-`
`Na^(+) e^(-) rarr Na(E_("cell")^(0) = -2.71 V)`
`H^2 + e^(-) rarr (1)/(2) H_2 + OH^(-)`
(i) At anode, two reaction are possible
`Cl^(-) rarr 1/2 Cl_2 + e^(-),E_("cell")^(@) = 136 V`
`2H_2O rarr O_2 + 4H^+ 4e^-, E_("cell")^(@) = 123 V`.
(ii) The reaction at anode with lower value of `E^@` Should be preferred, but oxidation of `O_2` is kinetically show process and needs hight voltage thus reaction (i) takes place.