GCSE · Chemistry · AQA · Spec 8462

Metal oxides and oxidation

Heat shiny copper in a flame and it turns black. Nothing has burnt away — the copper has picked something up from the air. What, and what's that change called?

Sort it · Follow the oxygen

Oxidised or reduced?

Each card shows one change. Look at the substance on the LEFT of the arrow. Did it gain oxygen or lose oxygen? Pick a card, then put it in a column.

Still to sort

Oxidised (0)

The substance has gained oxygen.

Where the line is: It started with no oxygen and ended up joined to oxygen, as part of an oxide.

Reduced (0)

The substance has lost oxygen.

Where the line is: It started as an oxide and ended up without that oxygen. An oxide on the left is a clue, not a verdict.

6 of 6 still to sort.

Notice the pairs: the same metal can go either way. What decides it is the direction the oxygen moves.

Exam line: Always name the substance and say what happened to its oxygen: 'the copper gains oxygen, so it is oxidised.'

Watch out: Seeing the word 'oxide' is not the same as oxidation. An oxide that loses its oxygen has been reduced.

Zoom in: magnesium meets oxygen

Tap each part of the equation and watch where the oxygen ends up.

Tap a molecule to see what it does in the reaction.

What do you really think?

Where did the magnesium go?

A strip of magnesium is heated. It burns with a dazzling white flame and leaves a white powder behind.

Which of these is closest to what you think is going on?

Burning destroys some of the magnesium, so the white powder is what's left over — less stuff than we started with.The magnesium loses oxygen when it burns — that's why it's called oxidation.It only counts as oxidation because there's a flame. No flame, no oxidation.The magnesium has joined with oxygen from the air to make magnesium oxide, so it has gained oxygen.

How sure are you?

I'm sureI think soI'm guessing

Burning destroys some of the magnesium, so the white powder is what's left over — less stuff than we started with.

This is a common misconception

Burning looks like destruction, but nothing is burnt away here. The magnesium combines with oxygen from the air, and the white powder is magnesium oxide. The magnesium hasn't gone anywhere — it's in the powder, now joined to oxygen. So if you could catch every speck of that powder, it would weigh more than the magnesium you started with, because oxygen has been added.

The magnesium loses oxygen when it burns — that's why it's called oxidation.

This is a common misconception

This is the swap that catches the most people. Oxidation is GAIN of oxygen. The magnesium started with no oxygen at all and ended up combined with it. Losing oxygen is the opposite change, and it has a different name: reduction.

It only counts as oxidation because there's a flame. No flame, no oxidation.

This is a common misconception

The flame just tells you this reaction is fast and gives out lots of energy. It isn't the test. Copper heated in air doesn't burst into flames, but it still turns into copper oxide — it still gains oxygen, so it is still oxidised.

The magnesium has joined with oxygen from the air to make magnesium oxide, so it has gained oxygen.

This matches the evidence

Spot on. You followed the oxygen from the air into the powder. The magnesium gained oxygen, which is why the change is called oxidation.

Don't judge by the flame or by the word 'oxide'. Ask one question: did this substance gain oxygen or lose it?

Your turn to explain

Write it, then mark it

Zinc is heated in oxygen and forms zinc oxide. (a) Explain why this is an oxidation reaction. (b) Zinc oxide can be changed back into zinc. Explain why that change is a reduction. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

(a) The zinc gains oxygen / combines with oxygen. (1 mark)
(a) Gain of oxygen is oxidation (so the zinc is oxidised). (1 mark)
(b) The zinc oxide loses its oxygen / the oxygen is removed from it. (1 mark)
(b) Loss of oxygen is reduction (so the zinc oxide is reduced). (1 mark)

Model answer

(a) When zinc reacts with oxygen, the zinc combines with the oxygen to make zinc oxide, so the zinc has gained oxygen. Gaining oxygen is oxidation, so the zinc is oxidised. (b) When zinc oxide is turned back into zinc, the oxygen is taken away from it, so the zinc oxide loses oxygen. Losing oxygen is reduction, so the zinc oxide is reduced.

Say which way the oxygen went, then name the change. Gain of oxygen: oxidation. Loss of oxygen: reduction.

Exam line: Each half of the answer needs two things: what happened to the oxygen, and the name of the change.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Follow the oxygen: gain it and you're oxidised, lose it and you're reduced.

What you need to know

Metals react with oxygen to produce metal oxides.
Oxidation is the gain of oxygen.
Reduction is the loss of oxygen.
To explain a change, say which substance gained or lost oxygen, then name the change.

The big picture

When a metal reacts with oxygen it forms a metal oxide. The metal has gained oxygen, so the reaction is an oxidation. The opposite change is reduction: a substance that loses oxygen has been reduced. To decide which is happening, follow the oxygen.

Key points

1Metal + oxygen → metal oxide, for example magnesium + oxygen → magnesium oxide.

2A metal reacting with oxygen is an oxidation reaction, because the metal gains oxygen.

3A substance that loses oxygen is reduced — for example, copper oxide giving up its oxygen to leave copper.

4An 'oxide' in the name is not the verdict: check whether the substance gained its oxygen or lost it.

.we-_R_18slubsnpfiv5ubrb_ [data-we-step]{display:flex !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-solution]{display:block !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-reveal]{display:none !important}

Worked example

Problem

Tin is heated in air and forms tin oxide. Is the tin oxidised or reduced? Explain your answer.

⚠ Watch out

Swapping the two definitions — saying a metal that reacts with oxygen has 'lost' oxygen, or calling any change with an oxide in it 'oxidation'. Oxidation is gain of oxygen; reduction is loss of oxygen.

🧠

Memory hook

Follow the oxygen. Oxygen ON: Oxidised (the two O-words go together). Oxygen off: reduced.

✓

Check yourself

Cover the page. Lithium reacts with oxygen to make lithium oxide. Is the lithium oxidised or reduced, and what is your reason in one short phrase? (Check: oxidised, because the lithium gains oxygen.)

Flashcards

(7)

What do metals form when they react with oxygen?

Metal oxides — for example, magnesium + oxygen → magnesium oxide.

Oxidation, in terms of oxygen

Gain of oxygen.

Reduction, in terms of oxygen

Loss of oxygen.

Why is a metal reacting with oxygen called an oxidation reaction?

Because the metal gains oxygen.

An oxide changes into its metal. Oxidised or reduced?

Reduced — the oxide has lost its oxygen.

Does 'oxide' in the starting substance mean the change is oxidation?

No. Check the direction: an oxide that loses its oxygen is reduced.

Does a substance have to burn with a flame to be oxidised?

No. Copper heated in air doesn't burn, but it still gains oxygen to form copper oxide, so it is oxidised.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

Oxidised or reduced?

Where did the magnesium go?

Write it, then mark it

More AQA GCSE Chemistry topics