Testing for hydrogen
Hydrogen is colourless and has no smell. So how do we know a tube holds hydrogen? By setting light to it.
Activity 16.8
- Set up the apparatus shown in figure 16.2 and collect several samples of hydrogen (H2) gas (since a gas jar needs a large volume of gas, use about five test tubes instead).
- Close the mouth of the tube holding the collected gas sample firmly, take it out of the water, and insert a lighted splint into the tube.
(Carry out this activity with your science teacher.)
The observation
The gas burns with a "pop" sound.
The identifying test
By this means hydrogen (H2) gas can be identified easily. The "pop" is its signature.
Why is there a sound?
The hydrogen in the tube has mixed with the oxygen of the air. Bring a flame near and the mixture burns all at once — and that sudden combustion makes the "pop".
Do not confuse it with the oxygen test
For hydrogen a lighted splint is used and a "pop" results. For oxygen a glowing splint is used and it relights. Both the apparatus and the result differ.