Question

For the reduction of $NO^-_3$ ion in an aqueous solution $E^\circ$ is $+ \,0.96\, V$. Values of $E^\circ$ for some metal ions are given below $\, V^{2+}(aq)+2e^- \longrightarrow V;\, \, \, \, \, E^\circ = -1.19\, Vtt$ $\, Fe^{3+}(aq)+3e^- \longrightarrow Fe;\, \, \, \, \, E^\circ = -0.04 V$ $Au^{3+}(aq)+3e^- \longrightarrow Au;\, \, \, \, \, E^\circ = +1.40\, V$ $Hg^{2+}(aq)+2e^- \longrightarrow Hg;\, \, \, \, \, E^\circ = +0.86 V$ The pair(s) of metals that is/are oxidised by $NO^-_3$ in aqueous solution is (are)

• A. $V$ and $Hg$
• B. $Hg$ and $Fe$
• C. $Fe$ and $Au$
• D. $Fe$ and $V$

Answer 1

Answer: (D)

$Fe$ and $V$

Answer 2

Metals with $E^\circ$ value less than 0.96 V will be able to reduce $NO^-_3$
in aqueous solution.Therefore, metals V ($E^\circ$ = - 1.19 V),
Fe ($E^\circ$ = - 0.04 V), Hg ($E^\circ$ = 0.86 V) will all reduce $NO^-_3$ but Au
($E^\circ$ = 1.40 V) cannot reduce $NO^-_3$ in aqueous solution.