Testing for Oxygen & Carbon Dioxide (WJEC GCSE Chemistry)
Revision Note
Testing for Oxygen & Carbon Dioxide
The test for carbon dioxide involves bubbling the gas through an aqueous solution of calcium hydroxide (limewater)
If the gas is carbon dioxide, the limewater turns milky or cloudy
Testing for carbon dioxide
Carbon dioxide is bubbled through limewater, which turns cloudy or milky
Examiner Tips and Tricks
Sometimes students write that extinguishing a burning splint indicates carbon dioxide gas
All this shows is that there is a lack of sufficient oxygen present to keep the flame going!
Other gases, such as nitrogen, will also do this
Therefore, extinguishing a flame is not definitive and should not be quoted in an exam answer.
Oxygen
The test for oxygen consists of placing a glowing splint inside a test tube of gas
If the gas is oxygen, the splint will relight
Testing for oxygen
Oxygen relights a glowing splint
Examiner Tips and Tricks
Sometimes the splint does not relight, but it glows very brightly, which is also a positive result.
In an exam, however, it is best to state that the oxygen gas relights the glowing splint
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