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

How to Test for Cations (Edexcel IGCSE Science (Double Award) (Modular)): Revision Note

Exam code: 4XSD1

Alexandra Brennan

Written by: Alexandra Brennan

Reviewed by: Philippa Platt

Updated on

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

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
Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry Content Creator / Senior Marketing Executive

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.

Philippa Platt

Reviewer: Philippa Platt

Expertise: Chemistry Content Creator

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener