IGCSEScienceOxford AQACombined Science Double AwardChemistryRevision NotesChemical AnalysisIdentification of ionsTest for Carbonates

Test for Carbonates (Oxford AQA IGCSE Combined Science Double Award)

Revision Note

Alexandra Brennan

Written by: Alexandra Brennan

Reviewed by: Stewart Hird

Oxford AQA Combined Science Double Award: ChemistryOxford AQA Chemistry

Test for Carbonates

  • Carbonates all contain the carbonate ion, CO32-

  • The test for this ion involves adding dilute acid and testing the gas released

  • If a carbonate compound is present then effervescence should be seen as CO2 gas is produced, which forms a white precipitate of calcium carbonate when bubbled through limewater:

CO32- (aq) + 2H+ (aq) → CO2 (g) + H2O (l)

CO2 (g) + Ca(OH)2 (aq) → CaCO3(s) + H2O(l)

  • The white precipitate turns limewater cloudy 

Testing for carbonate ions

The diagram shows carbon dioxide being bubbled through limewater, and the limewater turning milky / cloudy to confirm the presence of carbon dioxide
Limewater turns milky in the presence of carbon dixoide caused by the formation of insoluble calcium carbonate

Examiner Tips and Tricks

You’ll need to connect the test tube of the suspected ion to the test tube of limewater quickly so none of the CO2 escapes.

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    Alexandra Brennan

    Author: Alexandra Brennan

    Expertise: Chemistry

    Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

    Stewart Hird

    Author: Stewart Hird

    Expertise: Chemistry Lead

    Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.