Metals Meet Nitric Acid

Why it matters

Drop zinc into hydrochloric acid and hear the fizz of hydrogen. Drop it into nitric acid and the fizz vanishes, replaced by a silent, toxic redox dance.

The idea in plain words

Analyze the redox: Copper loses electrons to become blue Cu²⁺, while nitrogen in HNO₃ gains electrons to form NO gas.

Predict first

Why does nitric acid not release hydrogen gas with most metals?

Nitric acid is a powerful oxidizer. It oxidizes the hydrogen produced during the initial reaction into water, releasing nitrogen oxides (like NO or NO₂) instead.

• Nitric acid is too weak to react with metals
• Nitric acid is a strong oxidizing agent that converts any formed hydrogen into water — correct
• The metal forms a protective oxide layer instantly
• Hydrogen gas is absorbed by the solution

What you do

React copper and zinc with nitric acid. Observe the colour change for copper and the lack of hydrogen bubbles for both.

Check yourself

What is the primary reason hydrogen gas is not evolved when metals react with nitric acid?

Nitric acid is a strong oxidizing agent. It oxidizes the nascent hydrogen produced into water, resulting in the evolution of nitrogen oxides instead.

When copper reacts with nitric acid, the solution turns blue. What causes this?

The blue colour is characteristic of aqueous copper(II) ions, Cu²⁺, formed in the product copper(II) nitrate.

Based on the provided reaction data, what gas is produced when zinc reacts with nitric acid?

With dilute nitric acid, zinc gives nitrous oxide: 4Zn + 10HNO₃ → 4Zn(NO₃)₂ + 5H₂O + N₂O. (Concentrated HNO₃ gives NO₂.)

• Nitric acid does not contain hydrogen atoms
• The hydrogen formed is oxidized to water by the nitric acid — correct
• The reaction requires heat to release hydrogen
• Metals do not react with acids to form gases
• Formation of copper(II) nitrate, Cu(NO₃)₂ — correct
• Formation of copper(I) oxide
• Dilution of the acid
• Presence of nitrogen dioxide gas dissolved in water
• Hydrogen (H₂)
• Nitrous oxide (N₂O) — correct
• Nitrogen dioxide (NO₂)
• Ammonia (NH₃)