Identification of Gases (Cambridge (CIE) O Level Chemistry): Revision Note
Exam code: 5070
Identification of Gases
Several tests for anions and cations produce gases which then need to be tested
The table below indicates the tests for the gases included in the syllabus
Gas | Appearance of gas | Test | Result |
|---|---|---|---|
Ammonia (NH3) | Colourless with a pungent smell | Damp red litmus paper | Turns blue |
Carbon dioxide (CO2) | Colourless and odourless | Bubble through limewater | Limewater turns milky/cloudy |
Chlorine (Cl2) | Pale green with a choking smell | Damp blue litmus paper | Turns red and is quickly bleached to white |
Hydrogen (H2) | Colourless and odourless | Hold a lighted splint at the mouth of the test tube | Burns with a squeaky pop sound |
Oxygen (O2) | Colourless and odourless | Hold a glowing splint at the mouth of the test tube | The splint relights |
Sulfur dioxide (SO2) | Colourless with a pungent choking smell | Add to acidified aqueous potassium manganate(VII) | Turns from purple to colourless |
Examiner Tips and Tricks
It is easy to confuse the tests for hydrogen and oxygen. Try to remember that a ligHted splint has a H for Hydrogen, while a glOwing splint has an O for Oxygen.
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