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OCR GCSE Chemistry B · J258
OCR J258 Check the specification (PDF) (opens in a new tab)
Interpret flame tests to identify metal ions (lithium, sodium, potassium, calcium, copper).
Chemists use qualitative analysis to find out what is in an unknown sample. A can help identify a in a compound such as a salt. When the sample is heated in a flame, it may produce a characteristic colour. Compare the colour you observe with known flame-test colours to suggest which metal ion is present. The test identifies the metal ion, not the entire compound.
Heat gives energy to electrons in particles containing the metal. When the electrons lose that energy, light is emitted. Different metals can produce different visible colours, which makes the observation useful for identification.
| Metal ion | Flame colour |
|---|---|
| Lithium, | Crimson red |
| Sodium, | Yellow or yellow-orange |
| Potassium, | Lilac |
| Calcium, | Orange-red or brick red |
| Copper, | Blue-green |
For example, if an unknown sample gives a lilac flame, that observation points to potassium ions. A blue-green flame points to copper ions. Colour descriptions can vary slightly: calcium’s orange-red may be called brick red, whereas lithium’s red is usually described as crimson.
A clear colour is most useful when testing a single metal ion. If a sample contains more than one, colours can overlap; sodium’s strong yellow can hide another ion’s colour. A flame-test result is therefore evidence for an ion, but it does not necessarily show every ion in a mixture.
Crimson red → ; yellow or yellow-orange → ; lilac → ; orange-red or brick red → ; blue-green → .
A flame colour suggests a metal ion, not the identity of the whole compound. In a mixture, a strong colour—especially sodium’s yellow—may mask another colour.
Match the observed flame colour to the metal ion, not to the whole compound.
Describe calcium as orange-red or brick red; do not confuse it with lithium’s crimson red.
A strong yellow sodium colour can mask other colours in a mixture, so a flame test may not identify every ion present.
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Last updated
Positive ion (cation)
A positively charged particle formed when an atom loses one or more electrons.
Flame test
A chemical test that uses the colour produced by a heated sample in a flame to help identify a metal ion.
Qualitative analysis
Analysis that identifies which substances or ions are present, rather than measuring how much is present.
Put your knowledge into practice — try past paper questions for Chemistry B
Positive ion (cation)
A positively charged particle formed when an atom loses one or more electrons.
Flame test
A chemical test that uses the colour produced by a heated sample in a flame to help identify a metal ion.
Qualitative analysis
Analysis that identifies which substances or ions are present, rather than measuring how much is present.