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: Positively charged ion

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TEST FOR AMMONIUM ION NH4+

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TEST FOR AMMONIUM ION

Diagram showing the Test for Ammonium Ion

METHOD: Add Aqueous Sodium Hydroxide to the solid or solution and heat using bunsen burner Lower damp red litmus paper into gas produced

RESULT: If Ammonium ions are present, pungent-smelling gas is produced Gas produced turns damp red litmus paper Blue

EQUATION:          NH4+ (aq)            +              OH-            →              NH3              +            H2O     Ammonium Ions               Hydroxide Ions (from Solution Tested)   (from Sodium Hydroxide)

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TEST FOR Cu2+, Fe2+ and Fe3+

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TEST FOR Cu2+, Fe2+ and Fe3+
Diagram showing the Test for Cu2+, Fe2+ and Fe3+
METHOD: Add Aqueous Sodium Hydroxide Colour of precipitate is observed and recorded
RESULT AND EQUATION:
METAL CATION	COLOUR OF PRECIPITATE	EQUATION
COPPER (II)      Cu2+	Blue Precipitate	Cu2+    +    2OH-    →    Cu(OH)2
IRON (II)             Fe2+	Green Precipitate	Fe2+    +    2OH-    →    Fe(OH)2
IRON (III)            Fe3+	Brown Precipitate	Fe3+    +    3OH-    →    Cu(OH)3