The tests and positive results for hydrogen, oxygen, carbon dioxide and chlorine, and which reactions give which gas.
What you will learn
- Describe the test and result for hydrogen, oxygen, carbon dioxide and chlorine
- Predict which gas a reaction gives off
- Identify gases from a table of results
Four tests to know
- Hydrogen: hold a burning splint at the open end of the tube. It burns with a squeaky pop.
- Oxygen: put a glowing splint into the tube. It relights.
- Carbon dioxide: bubble it through limewater (calcium hydroxide solution). It turns milky: insoluble calcium carbonate forms.
- Chlorine: hold damp litmus paper in it. It is bleached white (blue litmus may go red first). Do it in a fume cupboard: chlorine is toxic.
Glowing splint for oxygen, burning splint for hydrogen: mixing these two up is the commonest slip.
A glowing splint is used for oxygen because it relights only in oxygen, so the result is clear. The litmus paper must be damp because chlorine has to dissolve in the water on it before it can bleach it.
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Four tests to know
- Where the gases come from
- Try it: Test and result
10 practice questions, marked as you go; about 15 minutes in all.
Key terms
Squeaky pop, Glowing, Relights, Limewater, Damp litmus paper, Hydrogen, Carbon dioxide, Oxygen, Chlorine
In this unit: Chemical analysis
Purity and formulations, chromatography and Rf values, tests for gases, and for separate Chemistry the tests for ions and flame emission spectroscopy.