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The test for oxygen is to put a glowing splint into a test tube of the gas: if oxygen is present, the splint relights. Free notes and 9 questions answered.
Testing for Oxygen Gas is part of Identification of common gases in GCSE AQA Higher Chemistry.
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The test for oxygen is to put a glowing splint into a test tube of the gas: if oxygen is present, the splint relights. Free notes and 9 questions answered.
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Use this lesson to stay inside Identification of common gases while connecting the detail back to the wider Topic 8: Chemical analysis topic.
Read the core explanations from Testing for Oxygen Gas before testing yourself from memory.
Oxygen is everywhere around us, but how do you prove it's there? You can't see it, smell it, or taste it. Yet oxygen is crucial for combustion - without it, nothing burns. This invisible gas has a signature behaviour that gives it away every time.
In chemistry practicals, you'll often produce gases and need to identify them. Oxygen might be released when you decompose hydrogen peroxide, or when plants photosynthesise. The glowing splint test is your go-to method for confirming oxygen's presence.
Here's what happens step by step. You light a wooden splint, then blow it out so it's no longer flaming but still glowing red-hot at the tip. When you insert this glowing splint into a test tube containing oxygen, something dramatic happens - the splint bursts back into flame.
**Trap**: Many students think any hot object will relight in oxygen. Actually, the splint needs to be glowing (around 250°C) to provide the activation energy for combustion. A cold splint won't work.
Worked example: Performing the Oxygen Test
Test an unknown gas to see if it contains oxygen
Answer: If oxygen is present, the glowing splint will relight. If not, it will just go out.
The science behind this test is all about combustion. When wood burns, it needs three things: fuel (the wood), heat (from the glowing tip), and oxygen. Remove any one of these and combustion stops.
In normal air (21% oxygen), a glowing splint will eventually go out because there isn't enough oxygen concentration to sustain combustion. But in pure oxygen or oxygen-rich mixtures, there's plenty of oxygen molecules available. The glowing tip provides enough heat energy to start the combustion reaction again.
The key is oxygen concentration. Air contains about 21% oxygen, which isn't quite enough to relight a glowing splint. But if your gas sample contains 30% or more oxygen, you'll see that dramatic relighting effect.
You'll encounter oxygen in several classic chemistry experiments. Knowing where it comes from helps you predict when to use this test.
The most common source is decomposing hydrogen peroxide with manganese dioxide catalyst: $2H_2O_2 \rightarrow 2H_2O + O_2$. The oxygen gas bubbles off and can be collected in a test tube for testing.
Electrolysis of water also produces oxygen at the positive electrode (anode): $4OH^- \rightarrow 2H_2O + O_2 + 4e^-$. You'll see bubbles forming that you can test with a glowing splint.
Exam questions about gas tests are straightforward if you know the exact wording examiners expect. For oxygen, you must mention both the glowing splint AND the relighting.
**Common exam mistake**: Writing 'the splint lights up' instead of 'the splint relights'. The examiner wants to see you understand the splint was already glowing before being inserted into the gas.
The glowing splint test is reliable, quick, and requires no special equipment. It's been used by chemists for centuries because oxygen's role in combustion makes it uniquely detectable this way. Master this test and you'll never struggle to identify oxygen in your practicals.
Exam precision note: In Testing for Oxygen Gas - Test for oxygen - Identification of common gases, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
The oxygen test is a qualitative test. A glowing splint relights because oxygen supports combustion. In exam answers, the key point is the observation: the splint relights. Simply saying that oxygen burns is not precise enough because the splint is already glowing before the test is done.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The test for oxygen is to put a glowing splint into a test tube of the gas: if oxygen is present, the splint relights. If oxygen is not present, the splint will just go out.
Oxygen relights a glowing splint because oxygen supports combustion: with a high concentration of oxygen, the glowing tip provides enough heat to start the combustion reaction again. Air contains only about 21% oxygen, which is not enough to relight the splint.
The glowing splint test is done by lighting a wooden splint in a Bunsen flame, then blowing it out gently so the tip is still glowing. The glowing end is quickly put into the gas sample before it cools; if the splint relights, oxygen is present.
The most common mistake in the oxygen test is writing that the splint lights up instead of saying the glowing splint relights. A correct answer shows that the splint was already glowing before it was put into the gas.
Oxygen is often made in the lab by decomposing hydrogen peroxide with a manganese dioxide catalyst: 2H₂O₂ → 2H₂O + O₂. It is also produced at the positive electrode (anode) during electrolysis of water.
A glowing splint doesn't relight in normal air because air is only about 21% oxygen, which isn't quite enough to relight it. A gas sample needs about 30% or more oxygen for the glowing splint to burst back into flame.
A qualitative test shows whether something is present, rather than how much of it there is. The glowing splint test is a qualitative test for oxygen: if the glowing splint relights, oxygen is present.
The splint must be glowing, at around 250°C, because the hot tip provides the activation energy for combustion. A cold splint won't relight in oxygen, so the splint is lit, blown out and quickly put into the gas while still glowing.
Combustion needs three things: fuel, heat and oxygen. In the glowing splint test, the wood is the fuel and the glowing tip provides heat, so the splint relights only if there is enough oxygen.