Testing for Ions – Flame Tests and Precipitation Reactions

One of the most colourful areas of chemistry is qualitative analysis — identifying unknown ions through characteristic colours and precipitates. With simple reagents and a Bunsen burner, students can turn invisible chemistry into visible results.

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Flame Tests

Different metal ions emit distinctive colours when heated in a flame because their electrons absorb energy and then release it as light of specific wavelengths.

Typical results:

Metal Ion	Flame Colour
Lithium (Li⁺)	Crimson red
Sodium (Na⁺)	Yellow
Potassium (K⁺)	Lilac
Calcium (Ca²⁺)	Orange-red
Copper (Cu²⁺)	Green-blue

Students clean a wire loop in hydrochloric acid, dip it into the sample, and hold it in the flame to identify the metal by its colour.

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Precipitation Reactions

For non-metal anions and transition metal cations, adding reagents produces coloured or white precipitates:

Examples:

• Add sodium hydroxide solution to identify metal hydroxides:

  • Copper(II): blue precipitate

  • Iron(II): green precipitate

  • Iron(III): brown precipitate

• Add silver nitrate solution to identify halides:

  • Chloride: white precipitate

  • Bromide: cream precipitate

  • Iodide: yellow precipitate

Each reaction gives students visible confirmation of the ions present.

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Skills Highlight

• Carrying out flame tests and chemical analysis safely

• Recording results accurately using observation tables

• Understanding ionic equations and solubility rules

• Linking colour changes to electron transitions and compound structure

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Why It Works in Teaching

Flame tests and precipitation reactions appeal to all senses — colour, pattern, and chemical reasoning. They help students connect observations with ionic theory, building confidence in practical skills and understanding of chemical identity.