Lithium, sodium and potassium are all alkali metals. A student carries out flame tests on compounds of each of these metals. State the flame colour observed for lithium, sodium and potassium, and explain why flame tests are described as qualitative tests.

Pearson Edexcel International GCSE Chemistry (4CH1) — 2.1 Group 1 (alkali metals) · State and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Lithium – red/crimson flame colour
Sodium – yellow/orange‑yellow flame colour
Potassium – lilac/violet flame colour

Flame tests are qualitative because they only identify the presence of a particular metal ion; they do not give any information about the amount or concentration of that ion.

Examiner tips

  • Use the exact flame colours for each metal; include the colour description in parentheses if needed.
  • Explain that a qualitative test tells you ‘what is present’ but not ‘how much’ – mention the lack of quantitative data.
  • Keep the answer concise – one sentence per point is sufficient for full marks.
  • Use UK spelling (e.g., colour).

Common mistakes

  • Mixing up the flame colours (e.g., giving potassium a green flame).
  • Failing to state that the test is qualitative, or confusing it with a quantitative test.

Mark scheme (4 marks)

  1. Lithium gives a red/crimson flame colour
  2. Sodium gives a yellow/orange-yellow flame colour
  3. Potassium gives a lilac/violet flame colour
  4. A qualitative test identifies which metal ion (cation) is present / tells you what is present, but does not measure how much / does not give a quantity or concentration

Key terms in this question

flame test · qualitative · alkali metals

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