Flame Tests and Metal Hydroxides

This lesson covers flame tests and the reactions of metal ions with sodium hydroxide solution to form coloured precipitates, as required by the AQA GCSE Chemistry specification (8.1.2). These tests are used to identify the metal ions present in a compound. You need to know the flame colours for specific metal ions and the precipitate colours produced when sodium hydroxide is added to solutions of metal ion compounds.

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Flame Tests

A flame test is used to identify certain metal ions in a compound by the characteristic colour they produce when heated in a flame.

How to Carry Out a Flame Test

1. Clean a nichrome wire loop by dipping it in concentrated hydrochloric acid and holding it in a blue Bunsen burner flame until it produces no colour.
2. Dip the clean wire loop into the concentrated hydrochloric acid again.
3. Dip the wire loop into the sample (solid or solution) to be tested.
4. Hold the wire loop in the blue Bunsen burner flame.
5. Observe the colour of the flame produced and compare with known flame colours.

Why Clean the Wire?