GCSE CHEMISTRY - What are the Tests for Gases? - How do I test for a Gas? - How are Gases Tested?

There are general tests for gases. Some gases have a specific test.

General Tests.

1) Does the gas have a colour?

2) Does the gas have a smell?
All gases that smell are poisonous
(but not all poisonous gases smell, eg. carbon monoxide).

3) Does the gas change the colour of moist litmus paper
or moist universal indicator paper?

Some gases are acid or alkaline in water.
Using moist paper allows a little of the gas to dissolve in the water,
to form acid ions (H⁺), or alkaline ions (OH^-).

Acid ions will turn blue litmus paper to red,
or universal indicator paper to orange or red.

Alkaline ions will turn red litmus paper to blue,
or universal indicator paper to blue or purple.

4) Does the gas burn, or support burning?
Note that these two are not the same.
Some gases burn. Only oxygen will support burning.
Test with a lit splint.

Specific Test.

Some gases have a test which only that gas will perform.
The test is specific for the particular gas concerned.
It is the specific test that is the
one to remember, since it positively identifies the gas.

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