JEE Main · 2011 · 10 Apr 2011 · Offline · Redox Reactions and Electrochemistry

The reduction potential of hydrogen half cell will be negative if :

Answer: (B)

Solution

For the hydrogen electrode

2 H^{+} + 2 e^{-} \to H_{2}

, the Nernst equation with

E^{\circ} = 0

gives

E = - \frac{0.059}{2} lo g \frac{p _{H_{2}}}{[ H ^{+} ] ^{2}}

. The potential is negative when the logarithm is positive, that is when

p_{H_{2}} > [H^{+}]^{2}

. Of the conditions offered, a hydrogen pressure of

2 atm

with

[H^{+}] = 1.0 M

gives

\frac{2}{1 ^{2}} = 2 > 1

, making

E

negative.

JEE Main · 2011 · 10 Apr 2011 · Offline · Single correct option