Question

The standard reduction potential of $Z n$ and $Ag$ in water at $298 K$ are,
$Zn ^{2+}+2 e^{-} \rightarrow Zn ; E^{\circ}=-0.76 \,V$ and
$Ag ^{+}+e^{-} \rightarrow Ag ; E^{\circ}=+0.80 \,V$
Which of the following reactions takes place?

• A. $Zn ^{2+}{ }_{(a q)}+ Ag ^{+}{ }_{(a q)} \rightarrow Zn _{(a q)}+ Ag _{(s)}$
• B. $Zn _{(s)}+ Ag _{(a q)} \rightarrow Zn ^{2+}{ }_{(a q)}+ Ag ^{+}{ }_{(a q)}$
• C. $Zn ^{2+}{ }_{(a q)}+2 Ag _{(s)} \rightarrow 2 Ag ^{+}{ }_{(a q)}+ Zn _{(s)}$
• D. $Zn _{(s)}+2 Ag ^{+}_{(a q)} \rightarrow Zn ^{2+}{ }_{(a q)}+2 Ag _{(s)}$

Answer 1

Answer: (D)

The values of standard reduction potential of $Zn$ and $Ag$ suggest that $Zn$ would undergo oxidation (lower reduction potential) and $Ag$ would undergo reduction (higher reduction potential). So the cell reaction must be

$Zn +2 Ag ^{+} \rightarrow Zn ^{2+}+2 Ag$