Which gas is it? Testing common gases
Collect gases from different reactions, test each with a glowing splint, a burning splint, limewater and damp litmus, and identify it.
Core concept
Common gases can be identified by simple tests: oxygen relights a glowing splint, hydrogen pops, carbon dioxide turns limewater milky, ammonia turns red litmus blue
Topic: Gases
Most gases are colourless, so chemists identify them by tests. oxygen: A gas in the air that living things need to breathe and that fire needs to burn. All key words relights a glowing splint, because it helps things burn. Hydrogen burns with a squeaky pop when a lighted splint is held at the mouth of the tube. carbon dioxide: A gas we breathe out. Plants take it in to make their food. All key words turns limewater milky and puts out a flame. Ammonia has a sharp smell and turns damp red litmus paper blue, because it is alkaline. Nitrogen gives none of these results: it simply puts out a flame. Air is mostly nitrogen with about one fifth oxygen.
What you will learn
- Carry out the tests for oxygen, hydrogen, carbon dioxide and ammonia.
- Identify a gas from its test results.
- Link each gas to a reaction that produces it.
Before you start
- Know that acids and alkalis change the colour of litmus.
Materials
- Gas samples collected in test tubes, limewater, red litmus paper, wooden splints
Equipment
- Test tubes with stoppers, spirit lamp, tongs
Procedure
- Choose a gas sample and try the tests: glowing splint, burning splint, limewater and damp red litmus.
- Use the results to decide which gas it is.
- Place each sample under the right gas.