This page shows the main methods for generating and collecting the main four gases that are used in school science.
Hazards may be associated with certain gases so before generating a gas, make sure you are fully competent to do so and have the relevant safety information to hand. CLEAPSS or the SSERC can provide this information. The relevant Hazcard numbers are listed in each section.
Chlorine can be classed as Toxic, Irritant and a Danger to the environment.
This gas must be collected in a fume cupboard
14 cm3 of concentrated hydrochloric acid (Corrosive) is added to at least 3 g of potassium manganate(VII) (Oxidising, Harmful, Danger to the environment). Details can be found on CLEAPSS Recipe card 26 and CLEAPSS Hazcards 22A, 47A and 81.
An alternate method involves taking 5 mol dm-3 hydrochloric acid (Irritant) and adding it to 30 cm3 of recently purchased (10–14% available chlorine) sodium chlorate(I) solution (Corrosive). The mixture should be stirred well.
If the reaction is slow, it is often because old sodium chlorate(I) has been used. This will have less than the required 10% available chlorine (as it applies to both methods). Details can be found on CLEAPSS Recipe Card 26 and CLEAPSS Hazcards 22A, 47A and 89.
Always collect the gas by downward delivery.
Oxygen is classed as an oxidising agent.
The most common method involves taking 50 cm3 of 20 vol hydrogen peroxide (Irritant) and adding it slowly to manganese(IV) oxide powder (Harmful). Oxygen should be collected over water.
Details can be found on CLEAPSS Recipe Card 27 and CLEAPSS Hazcards 50, 60 and 69.
To make CO2, take 42 cm3 of 2 mol dm-3 hydrochloric acid (Irritant) and add it slowly to a pile of marble chips. CO2 should be collected by downward delivery or over water (slightly soluble).
Details can be found on CLEAPSS Recipe Card 26 and CLEAPSS Hazcards 20 and 47A.
Hydrogen is classified as extremely flammable
Hydrogen can be made by adding 28 cm3 of 3 mol dm-3 hydrochloric acid (Corrosive) slowly to a pile of zinc granules and 1 g of hydrated copper sulphate (Harmful).
The hydrogen should be collected by upward delivery or over water.
Details can be found on CLEAPSS Recipe Card 26 and CLEAPSS Hazcards 47A and 48.