IGCSEChemistryEdexcelChemistry (Modular)Unit 2Revision Notes6. Inorganic Chemistry: Part 2Chemical testsHow to Test for Cations

How to Test for Cations (Edexcel IGCSE Chemistry (Modular))

Revision Note

Alexandra Brennan

Expertise

Chemistry

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

Exam Tip

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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    Alexandra Brennan

    Author: Alexandra Brennan

    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.