Positive ions:

A Flame tests for metal ions:

Some metal ions make a Bunsen burner flame take on a specific colour.

Lithium red

Sodium yellow-orange

Potassium lilac

Calcium red

Barium apple green

B: Sodium hydroxide tests for metal ions:

Many metals form precipitates with sodium hydroxide solution (except Group I) These precipitates are the metal hydroxides. eg Cu²⁺_(aq) + 2OH^-(aq) ? Cu(OH)_2(s)

Aluminium hydroxide is white * Al(OH)₃

Calcium hydroxide is white Ca(OH)₂

Magnesium hydroxide is white Mg(OH)₂

Copper(II) hydroxide is blue Cu(OH)₂

Iron(II) hydroxide is green Fe(OH)₂ (goes brown on standing)

Iron (III) hydroxide is brown Fe(OH)₃

* Aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.

Ammonium ions react with sodium hydroxide solution to form ammonia.

Ammonia gas turns damp litmus paper blue.

Flame Tests (courtesy of Sky Learning)

The scientists show the students what happens when flammable solutions of various salts are sprayed into a Bunsen flame. Notice how the colours of the flames changed with the different salts. You should know what the various colours used are to identify the different ions in a solution.

Watch the flame test experiment below courtesy of Sky Learning www.skylearning.co.uk