Q. 7.102 - An Introduction to General, Organic, and Biological Chemistry

Question

Identify each of the following as an oxidation or a reduction: ($7.6$)

a. ${\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \to \mathrm{Mg}\left(\mathrm{s}\right)$

b. $2{\mathrm{I}}^{-}\left(\mathrm{aq}\right) \to {\mathrm{I}}_2\left(\mathrm{s}\right) +2{\mathrm{e}}^{-}$

c. $\mathrm{Li}\left(\mathrm{s}\right)\to {\mathrm{Li}}^{+} \left(\mathrm{aq}\right) + {\mathrm{e}}^{-}$

d. ${\mathrm{Co}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \to \mathrm{Co}\left(\mathrm{s}\right)$

Step-by-Step Solution

Answer

(a) The given reaction i.e. ${\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \to \mathrm{Mg}\left(\mathrm{s}\right)$ has undergone reduction

(b) The given reaction i.e. $2{\mathrm{I}}^{-}\left(\mathrm{aq}\right) \to {\mathrm{I}}_2\left(\mathrm{s}\right) +2{\mathrm{e}}^{-}$ has undergone oxidation

(c) The given reaction i.e. $\mathrm{Li}\left(\mathrm{s}\right)\to {\mathrm{Li}}^{+} \left(\mathrm{aq}\right) + {\mathrm{e}}^{-}$ has undergone oxidation

(d) The given reaction i.e. ${\mathrm{Co}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \to \mathrm{Co}\left(\mathrm{s}\right)$ has undergone reduction

Part (a) Step 1: Given information

We need to find that the reaction has undergone oxidation or reduction 

Part (a) Step 2: Explanation

We know that

When there is gain of electrons then the reaction will undergo reduction.

And in the given reaction i.e. ${\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \to \mathrm{Mg}\left(\mathrm{s}\right)$ two electrons are gained by magnesium

Therefore, The given reaction has undergone reduction 

Part (b) Step 1: Given information

We need to find that the reaction has undergone oxidation or reduction  

Part (b) Step 2: Explanation

We know that

When there is a loss of electrons then the reaction will undergo oxidation.

And in the given reaction i.e. $2{\mathrm{I}}^{-}\left(\mathrm{aq}\right) \to {\mathrm{I}}_2\left(\mathrm{s}\right) +2{\mathrm{e}}^{-}$ two electrons are lost by iodine

Therefore, The given reaction has undergone oxidation 

Part (c) Step 1: Given information

We need to find that the reaction has undergone oxidation or reduction   

Part (c) Step 2: Explanation

We know that

When there is a loss of electrons then the reaction will undergo oxidation.

And in the given reaction i.e. $\mathrm{Li}\left(\mathrm{s}\right)\to {\mathrm{Li}}^{+} \left(\mathrm{aq}\right) + {\mathrm{e}}^{-}$ one electron is lost by lithium

Therefore, The given reaction has undergone oxidation 

Part (d) Step 1: Given information

We need to find that the reaction has undergone oxidation or reduction  

Part (d) Step 2: Explanation

We know that

When there is a gain of electrons then the reaction will undergo reduction.

And in the given reaction i.e. ${\mathrm{Co}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \to \mathrm{Co}\left(\mathrm{s}\right)$ two electrons are gained by cobalt

Therefore, The given reaction has undergone reduction