Cations

Flame Tests Method: (Na⁺,Ca²⁺,K⁺,Li⁺,Cu²⁺)

1. Hold a platinum or nichrome wire into a non-luminous flame until no colour is observed.

2. Dip wire into HCl and then into the salt you want to test.

3. Hold the wire loop and salt into a non-luminous flame and observe the colour.

Observed flame colour: Na⁺

Yellow-Orange

Observed flame colour: Ca²⁺

Orange-Red

Observed flame colour: K⁺

Lilac

Observed flame colour: Li⁺

Red

Observed flame colour: Cu²⁺

Blue-Green

Precipitation Reaction

A precipitation reaction is one in which two solutions react to form an insoluble solid in a solution.

Precipitate Tests Method: (Fe²⁺,Fe³⁺,Cu²⁺)

1. Add 1cm³ of each metal ion solution to 3 separate test tubes.

2. Add NaOH in drops from a pipette.

   1. Observe the precipitate and write down the colour.

Observed Precipitate Colour: Fe²⁺ - Fe(OH)_{2 (s)}

Green Precipitate

Observed Precipitate Colour: Fe³⁺ - Fe(OH)_{3 (s)}

Brown Precipitate

Observed Precipitate Colour: Cu²⁺ - Ca(OH)_{3 (s)}

Blue Precipitate

Tests for Ammonium Ions Method: (NH₄⁺)

1. Add 1cm³ of an ‘unknown’ solution containing NH₄⁺ ions to a test tube.

2. Add 5 drops of NaOH to the test tube.

3. Test gas given off with amp red litmus paper.

Result: If Ammonium ions are present then NH₃ (ammonium) gas will be given off which turns the the damp red litmus paper blue.