Question

The standard reduction potential at ${25}^o$C for the following half reactions are given against each of them as follows:
$Z{n}^{2+}\left(aq\right)+2e^{-}\rightleftharpoons Zn\left(s\right),-0.76$ V
$C{r}^{3+}\left(aq\right)+3e^{-}\rightleftharpoons Cr\left(s\right),-0.74$ V
$2H^{+}\left(aq\right)+2e^{-}\rightleftharpoons H_2\left(g\right),+0.0$ V
$F{e}^{3+}\left(aq\right)+e^{-}\rightleftharpoons F{e}^{2+}\left(aq\right),0.77$ V
Which is the strongest reducing agent?

• A. $Zn\left(s\right)$
• B. $Cr\left(s\right)$
• C. $H_2\left(g\right)$
• D. $F{e}^{2+}\left(aq\right)$

Answer 1

Answer: (A)

$Zn\left(s\right)$

Given standard reduction potential at ${25}^o$C are:
$Z{n}^{2+}\left(aq\right)+2e^{-}\rightleftharpoons Zn\left(s\right),-0.76$ V
$C{r}^{3+}\left(aq\right)+3e^{-}\rightleftharpoons Cr\left(s\right),-0.74$ V
$2H^{+}\left(aq\right)+2e^{-}\rightleftharpoons H_2\left(g\right),+0.0$ V
$F{e}^{3+}\left(aq\right)+e^{-}\rightleftharpoons F{e}^{2+}\left(aq\right),0.77$ V
Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby get reduced. Higher is the reduction potential more is the tendency to get reduced and stronger is the oxidising agent.

or vice-versa.

Thus lower reduction potential species will be the stronger reducing agent.

$Z{n}^{2+}\left(aq\right)+2e^{-}\rightleftharpoons Zn\left(s\right),-0.76$ V having lowest reduction potential thus $Zn$ is the strongest reducing agent.