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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