Lab Tests for Gases

Test for oxygen :

Gas collected is able to relight a glowing splint (light a wooden splint, blow it out and then insert it quickly into the gas chamber)

Test for carbon dioxide :

  1. Bubbling carbon dioxide through lime water (calcium hydroxide) makes it cloudy due to solid precipitates of calcium carbonate.
    Ca(OH)2 (aq) + CO2 (g) --> CaCO3 (s) + H2O (aq)

  2. Putting a lit splint into the gas collection chamber will put out the fire, as CO2 does not support combustion.

  3. Dissolved carbon dioxide lowers the pH of a solution. Carbon dioxide reacts with water to form carbonic acid.
    CO2 (g) + H2O (aq) <==> H2CO3 (aq)

Test for nitrogen :

Nitrogen is extremely neutral and there does not change the color of moist litmus or indicator paper, neither does it have color or smell. It is also non-combustible and will put out a lit splint.

Test for hydrogen:

Burns with a 'pop' sound - which is actually a small explosion as hydrogen is extremely flammable!

Test for chlorine gas :

  1. It is green-yellow in color, and smells pungent.

  2. It turns moist litmus/universal indicator paper red, then white.

  3. Since it is not combustible, it puts out a lit splint just like carbon dioxide.

To absorb carbon dioxide :

Place a strong alkaline/base in solid form (pellets, flakes) such as sodium hydroxide (NaOH), potassium hydroxide (KOH) or lithium hydroxide (LiOH) to absorb carbon dioxide.