How to Test for Cations (Edexcel IGCSE Chemistry (Modular)) : Revision Note

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.

You've read 1 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry Content Creator

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

Reviewer: 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.

Download notes on How to Test for Cations