Question

Identify each of the following as an oxidation or a reduction:

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

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

c.${\mathrm{Cr}}^{3+}\left(\mathrm{aq}\right)+3{\mathrm{e}}^{-}\to \mathrm{Cr}\left(\mathrm{s}\right)$

d.$2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2\left(\mathrm{g}\right)$

Short answer

(a) The reaction is reduction reaction.

(b) The reaction is oxidation reaction.

(c) The reaction is reduction reaction.

(d) The reaction is reduction reaction.

Step-by-step solution

Part (a) Step 1: Given Information

We are given the equations and we have to find out whether these reactions are oxidation or a reduction.

Part (a) Step 2: Explanation

Now, in ${\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+{\mathrm{e}}^{-}\to 2\mathrm{Na}\left(\mathrm{s}\right)$

$1$electron is getting reduced from Na in product side and the reaction in which an atom loses its electron is called reduction.

Hence, the given reaction is reduction.

Part (b) Step 1: Given Information

We are given the equations and we have to find out whether these reactions are oxidation or a reduction.

Part (b) Step 2: Explanation

Now, in $\mathrm{Ni}\left(\mathrm{s}\right)\to {\mathrm{Ni}}^{2+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}$

$2$electron is getting add in Ni in product side and the reaction in which an atom gains its electron is called oxidation.

Hence, the given reaction is oxidation.

Part (c) Step 1: Given Information

We are given the equations and we have to find out whether these reactions are oxidation or a reduction.

Part (c) Step 2: Explanation

Now, in ${\mathrm{Cr}}^{3+}\left(\mathrm{aq}\right)+3{\mathrm{e}}^{-}\to \mathrm{Cr}\left(\mathrm{s}\right)$

$3$electron is getting reduced from Cr in product side and the reaction in which an atom loses its electron is called reduction.

Hence, the given reaction is reduction

Part (d) Step 1: Given Information

We are given the equations and we have to find out whether these reactions are oxidation or a reduction.

Part (d) Step 2: Explanation

Now, in $2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2\left(\mathrm{g}\right)$

$2$electron is getting reduced from H in product side and the reaction in which an atom loses its electron is called reduction.

Hence, the given reaction is reduction