Identifying gases (Edexcel GCSE Chemistry): Revision Notes
📚 Revision Notes
Identifying gases
It is important to use unique tests for different gases to avoid uncertainty in identification. Each test provides a distinct observation, helping to accurately identify the gas present.
infoNote
1. Oxygen (O₂)
Test: Oxygen supports combustion. Place a glowing splint inside a test tube containing the gas.
- Positive Result: The glowing splint relights, confirming oxygen is present.
infoNote
2. Hydrogen (H₂)
Test: Hydrogen ignites in air. Hold a lighted splint near the mouth of a test tube containing hydrogen.
- Positive Result: A squeaky pop sound indicates the presence of hydrogen.
infoNote
3. Carbon Dioxide (CO₂)
Test: Bubble the gas through limewater, which is a solution of calcium hydroxide.
- Positive Result: The limewater turns milky or cloudy white due to the formation of calcium carbonate, confirming carbon dioxide is present.
infoNote
4. Chlorine (Cl₂)
Test: Chlorine is an acidic gas and acts as a bleach. Use damp litmus paper to test for chlorine.
- Damp blue litmus paper: The paper first turns red, then white (bleached).
- Damp red litmus paper: The paper is bleached white directly.
- Positive Result: Bleaching of the litmus paper confirms chlorine is present.
