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Testing for Gases

There are general tests for gases
and some gases have a specific test.

What are the General Tests for Gases?

1)  Does the Gas have a Colour?

2)  Does the Gas have a Smell?

All gases that have a smell are poisonous
but not all poisonous gases have a smell
for example carbon monoxide
is a poisonous gas that does not smell.

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 make blue litmus paper turn red,
or universal indicator paper turn orange or red.

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

4)  Does the Gas Burn or Support Burning?

Note that these two are not the same thing.
Some gases burn. Only oxygen will support burning.
Test with a lit splint.


What is the Specific Test for a Gas?

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.


See also the methods used for collecting gases.

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