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 Tip
- 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 Tip
- 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
