Flame Tests
Master Flame Tests for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) chemistry topic: lithium burns crimson, sodium yellow, potassium lilac, calcium orange-red and copper green.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Flame tests identify metal ions by the colour they produce in a flame. This is a Triple-only topic.
A clean nichrome or platinum wire loop is dipped in the sample and held in a blue Bunsen flame. Five colours must be known: lithium gives crimson, sodium gives yellow, potassium gives lilac, calcium gives orange-red, and copper gives green.
The limitation is that if a sample contains a mixture of metal ions, some flame colours can be masked by others. Sodium's strong yellow in particular can hide the colours of other ions, which is why instrumental methods are often preferred.
Revision notes
The method
Dip a clean nichrome or platinum wire loop into the sample.
Hold it in a blue Bunsen flame and observe the colour produced. The wire must be clean, otherwise residues from a previous sample would give a false result.
The five colours
Lithium: crimson. Sodium: yellow. Potassium: lilac.
Calcium: orange-red. Copper: green. These five must be learned precisely, as the question usually asks for the ion given a colour or vice versa.
Limitations
If a sample contains a mixture of metal ions, some flame colours can be masked by others.
Sodium's strong yellow colour is particularly likely to hide other colours. This is why instrumental methods such as flame emission spectroscopy are often preferred.
Key points
- Flame tests identify metal ions by colour.
- Lithium gives crimson.
- Sodium gives yellow.
- Potassium gives lilac.
- Calcium gives orange-red and copper gives green.
- Mixtures can mask flame colours.
Worked examples
Example 1
State the flame colours produced by lithium, sodium and copper ions. [3 marks]
Model answer
Lithium gives crimson (1 mark). Sodium gives yellow (1 mark). Copper gives green (1 mark).
Example 2
Explain why the wire loop must be clean before a flame test. [2 marks]
Model answer
Any residue from a previous sample would also produce a flame colour (1 mark), which could mask or be mistaken for the colour of the sample being tested (1 mark).
Example 3
Explain one limitation of flame tests. [2 marks]
Model answer
If a sample contains a mixture of metal ions, some flame colours can be masked by others (1 mark), particularly the strong yellow of sodium, making identification unreliable (1 mark).
Common mistakes
Confusing lithium and calcium colours.
Lithium is crimson; calcium is orange-red.
Forgetting to clean the wire.
Residues give false colours.
Not knowing the limitation.
Masking in mixtures is the standard answer and is examinable.
Using a yellow Bunsen flame.
A blue flame is needed so the flame's own colour does not interfere.
Exam tips
- Learn all five colours precisely.
- Mention cleaning the wire when describing the method.
- Give masking in mixtures as the limitation.
- Remember this is a Triple-only topic.
Key terms
- Flame test
- A test identifying metal ions by flame colour.
- Nichrome wire
- The wire loop used to hold the sample.
- Masking
- When one flame colour hides another.
- Metal ion
- The positively charged particle identified by the test.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.