9.2C - Flame tests for metal ions

Characteristic flame colours

Some metal ions give characteristic flame colours when their compounds are heated.

Learn the ion, its charge and the exact flame colour together.

Name the metal ion clearly. An ion name or correct formula can identify it; both are useful when learning the table.

Use precise colour descriptions: blue-green for copper(II) and orange-red for calcium distinguish the expected observations.

Flame test method

A GCSE flame test uses a tiny amount of the solid and a clean flame-test wire loop. The loop is usually nichrome or platinum because these metals can be heated strongly and do not usually add their own strong flame colour.

[DIAGRAM: asset_name: flame_test_wire_loop_method: Flame test wire-loop method - diagram 1; asset_slug: 206_9_2c_flame_tests_for_metal_ions_diagram1; file: diagram_assets/206_9_2c_flame_tests_for_metal_ions_diagram1.png; recommended_method: deterministic_drawn; description: Exact monochrome Edexcel GCSE Chemistry 9.2C method diagram. Show a heatproof mat with a Bunsen burner labelled "blue flame while testing (shown monochrome)", a nichrome or platinum wire loop held at the edge of the flame, a small beaker labelled "hydrochloric acid for cleaning loop", a watch glass labelled "solid salt sample", and an observation box labelled "record colour word: red / yellow / lilac / orange-red / blue-green". Include a safety note label: "hot wire loop and open flame". The diagram must be entirely monochrome with white background and #6A6B6E linework/text; true flame colours must appear only as written words, not coloured flame fills. Deterministic drawing is required because the apparatus and sequence are assessed practical content.]

A suitable method is:

1. Put on eye protection and place the Bunsen burner on a heatproof mat.
2. Clean the wire loop by dipping it into hydrochloric acid supplied for the practical, then heating it in a blue Bunsen flame.
3. Repeat the cleaning until the loop gives no extra flame colour.
4. Dip the clean loop into the acid again, then use it to pick up a few grains of the solid sample.
5. Hold the loop at the edge of the blue flame.
6. Observe the flame colour immediately and record the colour word.
7. Clean the loop again before testing another solid.