Question

For the reduction of $NO_{3}^{-}$ ion in an aqueous solution, ${{E}^{{}^\circ }}$ is +0.96 V. Values of ${{E}^{{}^\circ }}$ for some metals ions are given below
${{V}^{2+}}(aq)+2{{e}^{-}}\to V\,\,\,\,{{E}^{{}^\circ }}=-1.19\,\,V$
$F{{e}^{3+}}(aq)+3{{e}^{-}}\to Fe\,\,\,\,\,{{E}^{{}^\circ }}=-0.04\,V$
$A{{u}^{3+}}+3{{e}^{-}}\to Au\,\,\,\,{{E}^{{}^\circ }}=+1.40\,V$
$H{{g}^{2+}}+2{{e}^{-}}\to Hg\,\,\,\,{{E}^{{}^\circ }}=+0.86\,V$
The pair(s) metals that is (are) oxidized 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

In the question for reduction of $NO_{3}^{-}$ ion in an aqueous solution ${{E}^{{}^\circ }}$ value is given as +0.96 V. If the standard reduction potentials (${{E}^{{}^\circ }}$) values of metal will be less than the value of $NO_{3}^{-}$ then only they can be able to get oxidized by $NO_{3}^{-}$ in aqueous solution. The question has multiple correct options.

Complete answer:
From your chemistry lessons you have learned about the standard reduction potential.
Standard reduction potential of a molecule is defined as the reduction potential of molecules in specific standard conditions. It is determined by subtracting the reduction potential for the reaction that is taking place at anode from the standard reduction potential of the reaction taking place at cathode.
In the question we have asked to find the metals which get oxidized by $NO_{3}^{-}$ ion in aqueous solution. Here , $NO_{3}^{-}$ will oxidize only those metals which will have lower standard reduction potential than $NO_{3}^{-}$.
So, the value of standard reduction potential($E{}^\circ$) of $NO_{3}^{-}$ is given as +0.96 V
Let us check the standard reduction potential value of metals that are given in the question,
So, the standard reduction potential value of V, Fe and Hg will be less than $NO_{3}^{-}$ thus they can get oxidized by $NO_{3}^{-}$.But the $E{}^\circ$value of Au that is +1.40 V is more than the standard reduction potential value of $NO_{3}^{-}$.

Thus the correct option will be (A), (B) and (D).

Note:
The reduction potential value of a given molecule is considered as the negative value of its oxidation potential. It measures the ability of any chemical species to acquire electrons and thus get reduced. The minus sign in the reduction potential is important because it is reverse of oxidation and it is used in determining the direction of any reaction. Reduction potential is measured in Volts or millivolts.