GCSE · Chemistry · AQA · Spec 8462

Test for oxygen

A splint that has almost gone out, with just a red glowing tip, bursts back into flame in a test tube of oxygen. That one moment is the whole test.

The test for oxygen

Open stages 3 and 4. That's where the test is actually decided.

Start with a glowing splintNot a flame. Just a red, glowing tip on the end of the splint.
Put it into the test tube of gasPush the glowing end into the test tube, so it meets the gas you are testing.

Why does it relight?

What is actually happening in the tube?

A splint with only a glowing tip goes into a test tube of oxygen, and it bursts back into flame.

Which explanation is closest to what you think right now?

The oxygen catches fire. The flame you see is the oxygen burning.The splint is still burning, just barely. Oxygen helps things burn, and the tube has far more oxygen than air, so the splint bursts back into flame.It doesn't matter if the splint is glowing or already lit. The oxygen makes it burn either way, so both work.Air has oxygen in it too, so a glowing splint would relight in a test tube of air as well.

How sure are you?

I'm sureI think soI'm guessing

The oxygen catches fire. The flame you see is the oxygen burning.

This is a common misconception

A really common idea, but it's the wrong way round. Oxygen doesn't burn. The thing burning is the wood of the splint. Oxygen is what burning needs: it supports burning, and the more oxygen there is around the splint, the more strongly the splint burns. So the flame is the splint, helped along by all that oxygen.

The splint is still burning, just barely. Oxygen helps things burn, and the tube has far more oxygen than air, so the splint bursts back into flame.

This matches the evidence

Exactly right. A glowing splint is only just burning. In ordinary air it simply keeps glowing or fades. In a tube of oxygen it suddenly meets far more of the gas that keeps burning going, so it relights. Oxygen supports burning; it does not burn itself.

It doesn't matter if the splint is glowing or already lit. The oxygen makes it burn either way, so both work.

This is a common misconception

This is the one that catches people out. A lit splint already has a flame, so it has nothing to relight. You would have no clear change to watch for. The test only works with a glowing splint, because relighting is the result you are looking for, and only a splint without a flame can relight.

Air has oxygen in it too, so a glowing splint would relight in a test tube of air as well.

This is a common misconception

You're right that air contains oxygen. But it's only some oxygen, mixed in with other gases, and that isn't enough to bring a glowing splint back to a flame. That's exactly why the test works: a relight tells you the splint has met far more oxygen than air can give it.

Oxygen doesn't burn; it helps things burn. A glowing splint is barely burning, so a tube of oxygen brings its flame back.

Reading the result

What the splint tells you, and what it doesn't

Choose what the splint does, then follow it to what you can conclude.

What the splint does

2 possible results.

On A glowing splint goes into a test tube of the gas. 2 branches to choose from.

Watch out: A splint that doesn't relight can't tell you the gas's name. It only rules oxygen out.

Your turn to write it

Say it the way that scores

Describe the test for oxygen. Give the result you would see if the gas is oxygen. [2 marks]

Your answer

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

The mark scheme

A glowing splint is put into (a test tube of) the gas. The word glowing is needed: a lit or burning splint does not get this point. (1 mark)
The splint relights. 'Burns brighter' or 'burns more' does not get this point, because a glowing splint has no flame to make brighter. (1 mark)

Model answer

Put a glowing splint into a test tube of the gas. If the gas is oxygen, the splint relights.

Two words carry this answer: glowing (never lit) and relights (never 'burns brighter').

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

One glowing splint, one thing to watch for, one gas identified.

What you need to know

You test for oxygen with a glowing splint: one with a red tip and no flame.
The glowing splint goes into a test tube of the gas you want to identify.
If the splint relights, bursting back into flame, the gas is oxygen.

The big picture

To test a gas for oxygen, put a glowing splint into a test tube of the gas. If the splint relights, the gas is oxygen. It works because oxygen supports burning: a splint that is only just burning bursts back into flame when it meets far more oxygen than air contains.

Key points

1Method: put a glowing splint into a test tube of the gas.

2Result for oxygen: the splint relights.

3Glowing, not lit: a lit splint already has a flame, so it has nothing to relight.

4Oxygen doesn't burn itself. It supports burning, and the splint is what burns.

5No relight means the gas is not oxygen, but the test can't tell you what the gas is.

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Worked example

Problem

A student tests three test tubes of gas, P, Q and R. In P, a glowing splint relights. In Q, a glowing splint does not relight. For R, the student used a lit splint, and it kept burning. What can the student conclude about each tube?

⚠ Watch out

Writing 'a lit splint' instead of 'a glowing splint', or saying the splint 'burns brighter' instead of 'relights'. The test needs a glowing splint, and the result for oxygen is that it relights.

🧠

Memory hook

Glow in, flame back: if the splint gets its flame back, the gas is oxygen.

✓

Check yourself

Cover the page and say it out loud, in order: what goes into the test tube, the one thing you watch for, and what that tells you about the gas.

Flashcards

(6)

What kind of splint do you use to test a gas for oxygen?

A glowing splint: a red tip with no flame.

Where does the glowing splint go?

Into a test tube of the gas you are testing.

What happens to a glowing splint in oxygen?

It relights: it bursts back into flame.

Does oxygen burn?

No. Oxygen supports burning. In this test, the splint is what burns.

Why doesn't a glowing splint relight in air?

Air contains only some oxygen, which is not enough to bring the flame back.

In the oxygen test, which part is the observation and which is the conclusion?

Observation: the splint relights. Conclusion: the gas is oxygen.

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.

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What is actually happening in the tube?

What the splint tells you, and what it doesn't

Say it the way that scores

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