Question

Following 2 sections can occur at cathode in electrolysis of aqueous sodium chloride. i. Na + + e - ----> Na (s) E 0 = -2.71 V ii. 2H​2o + 2 e - ----> H2 + 2OH - E 0 =-0.83V Which reaction takes place preferentially and why?

Answer 1

Na⁺  + e⁻   ==>  Na     E₀ = - 2.71 V

2 H₂O + 2 e⁻  ===>   H₂ + 2 OH⁻       E₀ = - 0.83 V

Here water has reduction potential of  -0.83 V and Sodium has - 2.71V.  Water can be reduced easily by any other element having reduction potential less than - 0.83.  So Water can be reduced easily by many metals.

Sodium cannot be reduced unless another metal has a reduction potential less than -2.71V.  

So  the second reaction of reduction of water, happens preferentially.