Metals Meet Acid

Why it matters

Drop a piece of zinc into dilute sulphuric acid and it starts to fizz furiously. Tiny bubbles of gas stream off the metal — and that gas can go POP.

Predict first

When zinc reacts with dilute sulphuric acid, which gas bubbles off?

Zinc + dilute sulphuric acid gives zinc sulphate and hydrogen gas: Zn + H₂SO₄ → ZnSO₄ + H₂. The fizzing bubbles are hydrogen.

• Oxygen
• Hydrogen — correct
• Carbon dioxide
• No gas is produced

What you do

Add zinc to dilute sulphuric acid and watch the reaction: Zn + H₂SO₄ → ZnSO₄ + H₂. Collect the gas and test it with a lit splint.

Check yourself

What are the two products when a metal reacts with a dilute acid?

The general rule is: metal + dilute acid → salt + hydrogen. For zinc and sulphuric acid the salt is zinc sulphate and the gas is hydrogen.

How can you test that the gas given off is hydrogen?

Hydrogen burns with a squeaky pop when a lit splint is brought near it. A relighting glowing splint tests for oxygen, and milky limewater tests for carbon dioxide.

What happens when copper is added to dilute sulphuric acid?

Copper lies below hydrogen in the reactivity series, so it is too unreactive to displace hydrogen from a dilute acid. Unlike zinc, copper does not react.

• A salt and hydrogen gas — correct
• A salt and oxygen gas
• Water and carbon dioxide
• Only a salt, with no gas
• A lit splint makes a squeaky pop sound — correct
• A glowing splint relights
• It turns limewater milky
• It turns blue litmus red
• Nothing — copper does not react with dilute acid — correct
• It fizzes and gives off lots of hydrogen
• It dissolves and gives off oxygen
• It explodes violently