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IGCSEScienceEdexcelScience (Double Award)ChemistryRevision Notes2. Inorganic ChemistryChemical TestsTests for Cations

Tests for Cations (Edexcel IGCSE Science (Double Award))

Revision Note

Stewart Hird

Written by: Stewart Hird

Reviewed by: Lucy Kirkham

Updated on

Edexcel Science (Double Award): ChemistryEdexcel ChemistryEdexcel Chemistry (Modular): Unit 2

Tests for cations

  • Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide 

  • If only a small amount of NaOH is used then normally the metal hydroxide precipitates

  • The table below contains the results for each of the cations included in the syllabus

  • If a precipitate is formed from NaOH then the hydroxide is insoluble in water

Metal ion

Effect of adding NaOH

Cu2+

Light blue precipitate formed

Fe2+

Green precipitate formed

Fe3+

 Brown precipitate formed 

NH4+

Ammonia gas is produced which turns damp red litmus paper blue

Examiner Tips and Tricks

Sometimes you may not see much of a precipitate because the cation you are testing is present is very small amounts. However, every a slight cloudiness or colour change can indicate a positive test result.

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    Author
    Reviewer
    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.

    Lucy Kirkham

    Author: Lucy Kirkham

    Expertise: Head of STEM

    Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.