Question

A piece of copper wire is placed in a solution of nitric acid. 1. Write the balanced net ionic equation. 2.Which species is reduced in this reaction?

Answer 1

Redox is a chemical process that involves changing the oxidation states of atoms. The actual or formal transfer of electrons between chemical species is defined by redox reactions, which usually include one species (the reducing agent) suffering oxidation (losing electrons) while another species (the oxidising agent) experiences reduction (gains electrons). The chemical species that loses an electron is said to have been oxidised, whereas the chemical species that gains an electron is said to have been reduced.

Complete answer:
Copper is a reddish-brown metal that is commonly used in plumbing and electrical wiring, and is probably best known in the United States as the penny. (However, since 1983, pennies have been manufactured of zinc encased in a paper-thin copper foil to give them their classic look.) Copper is oxidised by concentrated nitric acid, $HN{{O}_{3}}$ , to generate $C{{u}^{2+}}$ ions, and then the nitric acid is reduced to nitrogen dioxide, a toxic brown gas with a noxious odour:
$Cu\left( s \right)~\text{ }+~\text{ }4HN{{O}_{3}}\left( aq \right)~\text{ }\to \text{ }Cu{{(N{{O}_{3}})}_{2}}\left( aq \right)~\text{ }+~\text{ }2N{{O}_{2}}\left( g \right)~\text{ }+~\text{ }2{{H}_{2}}O\left( l \right)$
Copper is oxidised to $C{{u}^{2+}}$ in the presence of concentrated nitric acid. And nitrogen is reduced to nitric oxide as a nitrate ion.
$C u \rightarrow C u^{2+}+2 e^{-}$
And nitrate, $N(+V)$ is reduced to $\mathrm{NO}_{2}, N(+I V)$ given conc. nitric acid....
$\mathrm{NO}_{3}^{-}+2 \mathrm{H}^{+}+e^{-} \rightarrow \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)(i i)$
we take the sum $\ldots . .(i)+2 \times(i i)$ to eliminate the electrons $\mathrm{Cu}+2 \mathrm{NO}_{3}^{-}+4 \mathrm{H}^{+}+2 e^{-} \rightarrow \mathrm{Cu}^{2+}+2 \mathrm{NO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)+2 e^{-}$
to give
$\mathrm{Cu}+2 \mathrm{NO}_{3}^{-}+4 \mathrm{H}^{+} \rightarrow \mathrm{Cu}^{2+}+2 \mathrm{NO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)$
as the net ionic equation
or we can add $2 \times N O_{3}^{-}$ to both sides to give.
$\mathrm{Cu}+4 \mathrm{HNO}_{3} \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{NO}_{2}(\mathrm{~g}) \uparrow+2 \mathrm{H}_{2} \mathrm{O}(l)$ .

Note:
Many organic reactions are redox reactions because they include changes in oxidation levels but no clear electron transfer. For example, when wood is burned with molecular oxygen, the oxidation state of carbon atoms in the wood increases while the oxidation state of oxygen atoms drops, resulting in the formation of carbon dioxide and water. The oxygen atoms go through reduction and gain electrons, whereas the carbon atoms go through oxidation and lose electrons. In this reaction, oxygen is the oxidising agent and carbon is the reducing agent.