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Preparing gases and testing for them

Summary - collecting five important gases

You need to know how to collect gases produced in reactions by upward and downward delivery, over water and using a gas syringe. You need to be able to explain the method of collection if you are given information about the density and solubility of the gas concerned.

The table summarises the ways in which hydrogen, oxygen, carbon dioxide, ammonia and chlorine may be collected. Note that all these gases may be collected using a gas syringe.

Ways to collect gases

 HydrogenOxygenCarbon dioxideAmmoniaChlorine
less dense than air?yes  yes 
upward deliveryyes  yes 
denser than air? slightlyyes yes
downward delivery  yes yes
solubility in water?very lowlow lowvery highmoderate
over wateryesyesyes yes

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