Question

How would you represent a half cell in which H⁺ ions of conc. 0.2 M get reduced into hydrogen gas at atmospheric pressure?

Answer 1

The representation of a half-cell in which H⁺ ions of concentration 0.2 M are reduced to hydrogen gas at atmospheric pressure is written as

\[\ce{Pt_{(s)} | H2_{(g)} (1 atm) | H{^{+}_{(aq)}} (0.2 M)}\]

Where

Pt_(s): Platinum electrode (inert), used because hydrogen is a gas and cannot serve as an electrode itself.

H_2(g) (1 atm): Hydrogen gas at 1 atmosphere pressure.

`bb("H"_("aq")^+)` (0.2 M): Hydrogen ion of concentration 0.2 M (from an acid).

The reaction involved is

\[\ce{2H{^{+}_{(aq)}} + 2e− -> H2_{(g)}}\]

This is a standard hydrogen electrode (SHE) setup, except the acid concentration here is 0.2 M instead of 1 M.