Question

What happens when copper reacts with concentrated nitric acid? What is the colour of the gas released during the reaction?

Hint:

Nitrogen dioxide (NO$_2$) is a toxic gas, so reactions involving concentrated nitric acid should be performed in a well-ventilated area or under a fume hood.

Answer 1

When copper (Cu) reacts with concentrated nitric acid (HNO$_3$), it undergoes an oxidation-reduction reaction. The copper metal is oxidized to copperions (Cu$^{2+}$), which form a blue solution of coppernitrate (Cu(NO$_3$)$_2$). The concentrated nitric acid acts as the oxidizing agent, and the nitrogen in it is reduced. This reduction produces nitrogen dioxide (NO$_2$), which is a toxic gas with a characteristic reddish-brown color.