Specification Point 2.47:
Describe tests for these cations: NH4+ Using Sodium Hydroxide Solution and identifying the gas evolved, Cu2+, Fe2+ and Fe3+ using Sodium Hydroxide Solution

Cations: A positively charged ion.

Test for Ammonium Ion NH4+

Test for Ammonium Ion, Edexcel IGCSE Chemistry

The test for Ammonium Ion

Method:

  • Add aqueous sodium hydroxide to the solid or solution and heat
  • Lower damp red litmus paper into gas produced

Result:

  • If ammonium ions are present then a pungent-smelling gas is produced
  • The gas produced turns damp red litmus paper blue
  • The gas in ammonia evolved from ammonium ions reacting with hydroxide ions from the sodium hydroxide (see below).

Equation:

  NH4+ (aq)             +               OH-            →                    NH3          +         H2O

 Ammonium Ions               Hydroxide Ions

Test for Cu2+, Fe2+ and Fe3+

The test for Cu2+, Fe2+ and Fe3+

Method:

  • Add aqueous sodium hydroxide
  • Colour of precipitate is observed and recorded

Result and Equation:

Tests for cations, Edexcel IGCSE Chemistry

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.