Oxygen in, oxygen out

The idea

A substance that gains oxygen or loses hydrogen during a reaction is oxidised; a substance that loses oxygen or gains hydrogen is reduced.

The black coat

Heat shiny copper powder in air and its surface turns black. The black stuff is copper(II) oxide, CuO.

What has happened to the copper?

• It has joined with oxygen from the air
• It has lost some oxygen
• It has only got dirty

Follow the atoms

Press the button and watch the ringed atom. Then tap whether each substance was oxidised or reduced.

In or out

A substance that gains oxygen or loses hydrogen during a reaction is oxidised. A substance that loses oxygen or gains hydrogen is reduced.

In CuO + H₂ → Cu + H₂O: copper(II) oxide loses oxygen (reduced) and hydrogen gains oxygen (oxidised).

• Oxidised | Reduced
• Oxygen | gained | lost
• Hydrogen | lost | gained

Notes

A substance that gains oxygen or loses hydrogen during a reaction is oxidised; a substance that loses oxygen or gains hydrogen is reduced.

Check yourself

In 2Cu + O₂ → 2CuO, copper is …

In CuO + H₂ → Cu + H₂O, what happens to CuO?

In N₂ + 3H₂ → 2NH₃, nitrogen gains hydrogen. So nitrogen is …

• reduced, because it gains oxygen. Gaining oxygen is oxidation. Reduction is losing oxygen.
• oxidised, because it gains oxygen — correct. Yes! Gaining oxygen is oxidation.
• neither. Copper gained oxygen: it is oxidised.
• It is oxidised: it loses oxygen. Losing oxygen is reduction. Oxidation is gaining oxygen.
• It is oxidised: it gains hydrogen. CuO did not gain hydrogen. It lost oxygen.
• It is reduced: it loses oxygen — correct. Yes! The oxygen left CuO and joined hydrogen.
• reduced — correct. Yes! Gaining hydrogen is reduction.
• oxidised. Oxidation is gaining oxygen or losing hydrogen. Here hydrogen is gained.
• neither, only oxygen counts. Hydrogen counts too: gaining hydrogen is reduction.