The Role of Copper in Strengthening Brown Fumes of Nitric Acid

Why are the brown fumes of nitric acid stronger when copper is added to nitric acid and heated compared to when it is heated alone?

The Role of Copper in Enhancing Nitric Acid Fumes

This is because copper acts as a catalyst in the reaction between nitric acid (HNO₃) and copper (Cu), promoting the formation of nitrogen dioxide gas.

When copper is added to nitric acid and heated, the reaction between nitric acid and copper takes place. This reaction involves the oxidation of copper by nitric acid, leading to the formation of copper nitrate (Cu(NO₃)₂), water (H₂O), and nitrogen dioxide gas (NO₂). The nitrogen dioxide gas presents itself as brown fumes.

Copper acts as a catalyst in this reaction, providing a surface for the reaction to occur more readily. It accelerates the breakdown of nitric acid, facilitating the release of nitrogen dioxide gas. As a result, the presence of copper strengthens the brown fumes of nitric acid compared to when nitric acid is heated alone.