Question

Question:Consider the following reduction potentials:

$$\begin{gathered} {\mathbf{Co}}^{\mathbf{3}\mathbf{+}}\mathbf{+}\mathbf{3}\mathbf{e}\to \mathbf{Co}\mathbf{;}\mathbf{E}\mathbf{°}\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{26}\mathbf{V} \\ {\mathbf{Co}}^{\mathbf{2}\mathbf{+}}\mathbf{+}\mathbf{2}\mathbf{e}\to \mathbf{Co}\mathbf{;}\mathbf{E}\mathbf{°}\mathbf{=}\mathbf{-}\mathbf{0}\mathbf{.}\mathbf{28}\mathbf{V} \end{gathered}$$

a. When cobalt metal dissolves in 1.0 Mnitric acid,

will be the primary product (assuming

standard conditions)?

b. Is it possible to change the concentration of$\mathbf{HNO}\mathbf{3}$

to get a different result in part a?

Short answer

1. $C{o}^{2+}$will be the primary product.

No, we cannot get a different result by making any change in the concentration of$HN{O}_3$

Step-by-step solution

 Analyzing the given data

The given half-reactions are:

$$\begin{gathered} C{o}^{3+}+3e^{-}\underset{}{\to }Co\left(E°=1.26V\right) \\ C{o}^{2+}+2e^{-}\underset{}{\to }Co\left(E°=-0.28V\right) \end{gathered}$$

Determining whether Co3+ or Co2+ is the primary product when cobalt metal dissolves in 1.0 M nitric acid

When cobalt is a reactant, we get either Co³⁺orCo²⁺. The first half-reaction in the above two reactions has a greater potential to be reduced. This means that the second half-reaction can be more easily oxidized. So, the primarily oxidized one will be Co²⁺. Hence, Co²⁺will be the primary product

Determining whether it is possible to change the concentration of HNO3 to get a different result in part a

No, we cannot get a different resultby making any changes in the concentration of HNO₃because the reaction is dependent on the reduction potential of the reactants and not the concentration. Also, since the first half-reaction in the above two reactions has a greater potential to be reduced than the second half-reaction, the main product will always be Co^2+, irrespective of the concentration.