Test for oxygen — AQA GCSE Chemistry
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Test for oxygen explained
Oxygen is identified by its ability to relight a glowing splint.
Read the full explanation
A splint is lit, then blown out so that it still glows at the tip. This glowing splint is inserted into a test tube containing the gas. In air, the splint would fade, but in oxygen the glowing tip bursts back into flame because oxygen supports combustion more effectively than air. The key observation is relighting, not a pop. The splint must be glowing, not flaming, before insertion, and it should be lowered into the tube so the gas surrounds the tip. A burning splint popping would indicate hydrogen instead.
Your focus
- Describe the test for oxygen using a glowing splint inserted into a test tube.
- State the positive observation as the splint relighting.
- Explain why oxygen relights a glowing splint but air does not.
Test for oxygen exam tips
Marking Points
- State that a glowing splint is inserted into a test tube containing the gas.
- Describe the positive result as the splint relighting.
- Explain that oxygen supports combustion, so the glowing splint bursts into flame.
- Distinguish this from the hydrogen test, where a burning splint gives a pop rather than a glowing splint relighting.
- Note that the splint must be glowing, not still flaming, before it is inserted.
Examiner Tips
- 💡State the splint condition clearly: glowing, not burning, before insertion.
- 💡Use the exact observation 'relights' rather than vague descriptions such as 'it reacts'.
- 💡When comparing gases, link the oxygen test to supporting combustion and the hydrogen test to a pop sound.
Common Mistakes
- Using a burning splint for oxygen; the correct test uses a glowing splint, while a burning splint is used for hydrogen.
- Saying the splint 'burns brighter' instead of relighting; the correct observation is that the glowing splint relights.
- Leaving the splint flaming before insertion; the correct method extinguishes the flame so the splint is only glowing.