Identifying Gases
Chemistry: Cambridge International GCSE Supplement, topic 12.5.12
Identifying Gases
Different gases are identified by unique chemical tests, like glowing/lighted splints, or solutions, revealing properties like alkalinity, combustibility, or bleaching ability.
Testing for ammonia (NH3) gas
- A damp red litmus paper is used to spot ammonia gas.
- Ammonia turns damp red litmus paper blue.
- This happens because ammonia is an alkali gas.
Testing for carbon dioxide (CO2) gas
- Chemistry tests carbon dioxide with limewater (calcium hydroxide).
- Carbon dioxide makes limewater turn milky or cloudy.
- This reaction forms calcium carbonate, a white solid.
Testing for chlorine (Cl2) gas
- Chemistry uses damp blue or red litmus paper to identify chlorine.
- Chlorine bleaches the colour from damp litmus paper, making it white.
Testing for hydrogen (H2) gas
- Chemistry uses a lit splint to test for hydrogen.
- Hydrogen makes a 'pop' sound when it meets a lit splint.
- This test shows that hydrogen is flammable.
Testing for oxygen (O2) and sulphur dioxide (SO2) gases
- Chemistry uses a glowing splint test for oxygen. Oxygen relights the glowing splint.
- Chemistry tests sulphur dioxide with acidified potassium manganate(VII) solution.
- Sulphur dioxide changes purple manganate(VII) solution to colourless.
Test yourself on Identifying Gases
Which indicator paper is used to test for ammonia gas, and what is the expected colour change?
What is the specific test for oxygen gas?