Sunday, July 9, 2017

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

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