Analysing Gases

Edited by Jamie (ScienceAid Editor), Taylor (ScienceAid Editor)


Methods of Collection

  1. 1
    Over Water.
    One way for gases to be collected is over water, but this can only be done with gases that are insoluble or just slightly soluble in water, otherwise they would dissolve and you wouldn't be able to collect them. For example: carbon dioxide, oxygen and hydrogen. For this method, a container is filled with water, a test tube is also partially filled with water and inverted and submerged in the water - it remains full. A pipe is put under the test tube, and as gas bubbles up into the test tube, it forces water from it; so that the gas is collected in the tube.
    the collection of gas over water
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  2. 2
    Displace Air.
    Another, more simple method, is to displace air rather than water. If the gas has a density lower than that of air, it can be collected by upward delivery. If, on the other hand, the gas has a density higher than air, it must be collected by downward delivery, or it will escape.
    collection of gas by upward and downward delivery
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  3. 3
    The next method of collection is the gas syringe. It's not only for collecting gases, but also for measuring the volume of the gas collected.
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Gas Testing Method


Collect gas

Put in a burning match. It will pop.



Collect gas.

Put in a glowing match. It will reignite.

Carbon Dioxide


Bubble gas through lime water (CaOH).

The water will turn cloudy.

Sulphur Dioxide


Collect gas.

Bubble through orange potassium dichromate solution. Solution turns green.

Hydrogen Chloride


Collect gas.

Mix with ammonia gas. Forms dense white fumes.



Collect gas

Add damp red litmus paper. Paper turns blue.


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Categories : Applied

Recent edits by: Jamie (ScienceAid Editor)

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