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

This question was posed to me in a national level competition.

Asked question is from Electrochemistry in division Electrochemistry of Chemistry – Class 12

Answer 1

The correct option is (c) 3.73

For explanation I would say: Given, potential of hydrogen gas electrode = -0.22 V

Electrode reaction: H^+ + e^– → 0.5 H2

Applying Nernst equation,

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

E°(H+/H₂) = 0 for hydrogen gas electrode

-0.22 = 0.059 log H^+

-0.22 = -0.059pH

pH= 3.73.