Qualitative Analysis: Tests for Ions

Qualitative analysis involves identifying which ions are present in an unknown sample using chemical tests. For Edexcel A-Level, you need to know flame tests for metal cations, precipitation tests with sodium hydroxide, tests for common anions, and tests for gases. This is one of the most practical and frequently examined topics.

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Flame Tests

Flame tests identify metal ions by the characteristic colour they produce when heated in a Bunsen flame. Electrons are promoted to higher energy levels by the heat, and as they fall back down, they emit light of specific wavelengths.

Procedure

1. Clean a nichrome wire loop by dipping it in concentrated hydrochloric acid and holding it in a blue Bunsen flame until no colour is produced
2. Dip the clean wire into the sample (or into concentrated HCl and then into the solid)
3. Hold the wire in the edge of the blue flame and observe the colour

Flame Colours