GCSEChemistryWJECRevision Notes1. Chemical Substances, Reactions & Essential Resources1.4 The Ever-Changing EarthTesting for Oxygen & Carbon Dioxide

Testing for Oxygen & Carbon Dioxide (WJEC GCSE Chemistry): Revision Note

Exam code: 3410

Richard Boole

Written by: Richard Boole

Reviewed by: Caroline Carroll

Updated on

WJEC ChemistryWJEC Science (Double Award): Chemistry

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

Test 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

Test 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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Author
Reviewer
Richard Boole

Author: Richard Boole

Expertise: Curriculum Expert

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

Caroline Carroll

Reviewer: Caroline Carroll

Expertise: Head of Content Delivery

Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about delivering high-quality resources to help students achieve their full potential.