Testing for Gases
There are general tests for gases. Some gases have a specific test.
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-).
ions will turn blue litmus
paper to red,
or universal indicator paper to orange or red.
ions will turn red litmus paper to blue,
or universal indicator paper to blue or purple.
4) Does the gas burn, or support
Note that these two are not the same.
Some gases burn. Only oxygen will support burning.
Test with a lit splint.
gases have a test which only
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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