Question

What is the pH of HCl solution when the hydrogen gas electrode shows a potential of -0.22 V at standard temperature and pressure?

a) 2.17 

b) 2.98

c) 3.73

d) 3.14

Answer 1

Answer : c) 3.73

Explanation :

Given, potential of hydrogen gas electrode is = -0.22 V

Reaction on electrode :

       H+  +  e–   →   0.5 H2

By using Nernst equation,

E (H+/H₂) = E°(H+/H2) – 0.059 log (1/ [H+])

E°(H+/H₂) = 0 for SHE

(standard hydrogen electrode SHE, potential is always considered as 0)

-0.22 = -0.059 log (1/[H+])

-0.22 = 0.059 log (H+)

(By definition of pH = - log (H+)

-0.22 = -0.059 pH

   pH = 3.73

c) 3.73