Tests for gases

Many reactions produce gases which can help identify the mechanisms and products involved. It is therefore important to be able to test for several common gases.

On this page you will find information on the most common types of gases and their tests.

This page will be updated further in the near future, however here are some tests for common gases given off in reactions


To test for hydrogen a small sample can be ignited. Hydrogen will make a squeaky pop when lit in air, care needs to be taken with this test as large amounts of hydrogen are very explosive in air.

Hydrogen reacts very quickly with oxygen to form water.


Oxygen supports combustion so a good method of testing for oxygen is to take a glowing splint and place it in a sample of gas, if it re-ignites the gas is oxygen.

This is a simple but effective test for oxygen. There are sometimes confusions as the splint can create a pop very slightly on re-ignition, which sometimes is mistaken for hydrogen. A hydrogen pop is much more violent, sometimes enough to completely extinguish the splint.

 Carbon Dioxide

There are two tests for carbon dioxide. Firstly it will extinguish a flame, however, as any oxygen free gas will also extinguish a flame this is a poor gas test and may result in misidentification.

The best way of testing for Carbon dioxide is to bubble it through lime water. A positive test will result in the lime water turning milky. Lime water turns milky as the Calcium hydroxide (chemical name for limewater) reacts with carbon dioxide to form Calcium Carbonate which is insoluble in water and thus forms a milky white precipitate.