Test for hydrogen — AQA GCSE Combined Science
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Test for hydrogen explained
Hydrogen is identified by its reaction with a burning splint.
Read the full explanation
Collect the gas in a test tube, light a splint, then hold the burning splint at the open end of the tube. Hydrogen burns rapidly with oxygen from the air, producing a squeaky pop. The test works because hydrogen is flammable and reacts exothermically: 2H₂ + O₂ → 2H₂O. The pop is the rapid expansion of hot gases and water vapour. Do not insert the splint into the tube, because the gas may not be mixed with enough oxygen and the pop can be weaker or the flame may be extinguished. The test is assessed by describing the correct procedure and the positive result, and by distinguishing hydrogen from other gases such as oxygen, which relights a glowing splint.
Your focus
- Describe the procedure for the test for hydrogen using a burning splint.
- State the positive result: hydrogen burns rapidly with a pop sound.
- Explain why the splint is held at the open end of the test tube rather than inserted into it.
Test for hydrogen exam tips
Marking Points
- A burning splint is held at the open end of a test tube containing the gas.
- Hydrogen burns rapidly and produces a pop sound.
- The reaction is hydrogen reacting with oxygen from the air to form water: 2H₂ + O₂ → 2H₂O.
- The test is positive only when a burning splint is used, not a glowing splint.
- The splint should not be inserted deep into the test tube; it is held at the open end.
Examiner Tips
- 💡State both the procedure and the result: 'Hold a burning splint at the open end of the test tube; a pop sound shows hydrogen.'
- 💡Use the word 'burning' rather than 'lit' or 'glowing' when describing the splint.
- 💡If asked to compare tests, contrast the burning splint pop for hydrogen with the glowing splint relighting for oxygen.
Common Mistakes
- Using a glowing splint instead of a burning splint: a glowing splint tests for oxygen, not hydrogen; always light the splint first.
- Saying hydrogen relights a glowing splint: that is the oxygen test; hydrogen gives a pop with a burning splint.
- Inserting the burning splint into the tube: this can extinguish the flame or give a weak result; hold it at the open end.