Flame tests: six metal-ion colours and contamination limits
Identify the required metal-ion candidates from labelled flame observations while recognising that contamination or mixtures can affect what is seen.
Exam scope and assessment notes
Core and Extended · Chemistry 0971, 2026–2028. Interpret the supplied laboratory observations on paper; actual chemical tests require an appropriate supervised laboratory method. Cambridge states that IGCSE 0971 has the same subject content as IGCSE 0620, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Distinguish a positive metal ion from an anion in a salt.
- Recognise that apparatus contamination can affect an observation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a flame-test result primarily support in this required list?
What you will learn
- Describe flame testing in the appropriate supervised context and recall the six required colours.
- Use a flame result to support a cation candidate without claiming it identifies every ion in the whole compound.
Six required flame-test colours
Try recalling the result, then open this comparison. Read the test and observation together. Actual testing belongs to an appropriate supervised laboratory method.
Open the comparison reference
Lithium · Li⁺
- Flame colour
- Red
Sodium · Na⁺
- Flame colour
- Yellow
Potassium · K⁺
- Flame colour
- Lilac
Calcium · Ca²⁺
- Flame colour
- Orange-red
Barium · Ba²⁺
- Flame colour
- Light green
Copper(II) · Cu²⁺
- Flame colour
- Blue-green
Use the supplied candidate set and conditions. One observation does not establish every ion in a mixture or certify purity.
Use text-labelled colours rather than screen colour alone
The required flame colours are lithium Li⁺ red, sodium Na⁺ yellow, potassium K⁺ lilac, calcium Ca²⁺ orange-red, barium Ba²⁺ light green and copper(II) Cu²⁺ blue-green. The reference writes the colour names explicitly; a display's coloured decoration is not a measured flame spectrum or a guarantee of how an actual flame will look.
In an appropriate supervised flame-test method, a suitable clean holder or wire carries the sample into the specified flame and the colour is observed. Avoid contamination from an earlier sample and compare the blank/background according to the method. These pages interpret supplied observations, while actual flame handling requires the laboratory procedure and supervision.
Identify the supported cation, not an entire unknown salt
A lilac flame supports potassium among the supplied candidates; it does not identify whether the salt's anion is chloride, nitrate or another species. Likewise, calcium's orange-red result identifies a cation candidate rather than proving a particular complete formula. Combine separate appropriate evidence when both ions are needed.
Contamination or a mixture can change or mask an observed colour. A yellow result on a holder that also gives yellow before the unknown is applied is not reliable evidence that the original sample contains sodium. Do not silently assign every observation to the sample when the method introduces its own signal. Use cleaned apparatus, an appropriate blank and suitable further observations as the supervised method requires.
Pause and explain
The holder shows yellow before the unknown is added. What should be concluded from another yellow observation?
Worked example
A supplied unknown gives a lilac flame using a clean appropriate method. A separate ion test supports chloride. What do the two observations support?
Show the worked solution
- Lilac supports potassium K⁺ among the required flame-test candidates.
- The separate controlled chloride test supports Cl⁻.
- The two results together are consistent with potassium chloride, KCl, in the supplied simple single-salt model; the flame alone did not identify chloride.
Answer Consistent with KCl in the supplied simple model; potassium is supported by the flame and chloride by the separate ion test.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Recall the required flame colours for lithium, sodium and potassium ions.
Give me a hint
Give colour names rather than relying on a screen swatch.
Compare my reasoning
- Li⁺ gives red.
- Na⁺ gives yellow.
- K⁺ gives lilac under the required observations.
Li⁺ red; Na⁺ yellow; K⁺ lilac.
Look for these in your work
- All three ion/colour assignments are correct.
- The evidence is described in words.
Recall the required flame colours for calcium, barium and copper(II) ions.
Give me a hint
Distinguish the two greens and the orange-red entry.
Compare my reasoning
- Ca²⁺ gives orange-red.
- Ba²⁺ gives light green.
- Cu²⁺ gives blue-green.
Ca²⁺ orange-red; Ba²⁺ light green; Cu²⁺ blue-green.
Look for these in your work
- All three remaining ions are correctly matched.
- Barium and copper colour names remain distinct.
An unknown gives orange-red flame, but its anion is untested. A report calls it definitely pure calcium nitrate. Evaluate each part of the claim.
Give me a hint
Separate cation evidence, anion identity and purity.
Compare my reasoning
- Orange-red supports calcium Ca²⁺ among the required candidates under the stated suitable method.
- The flame does not identify nitrate rather than another anion.
- A single flame observation does not certify purity; appropriate separate evidence is needed.
Calcium is supported; nitrate and perfect purity are not established by that flame observation alone.
Look for these in your work
- The supported cation inference is retained.
- Anion and purity overclaims are identified.
Common mistakes
- Swapping lithium red and calcium orange-red.
- Treating barium light green as copper(II) blue-green.
- Using one flame result to identify an unknown anion.
- Ignoring a holder or blank that already gives the same colour.
What can you explain now?
Which required cation gives a lilac flame?
Compare with the explanation
Potassium, K⁺.
The flame supports the cation candidate; another test is needed for an unknown anion.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Recall all six flame colours and explain why blank contamination, unknown anions and purity claims need separate consideration.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.