Flame Emission Spectroscopy
Build confidence in Flame Emission Spectroscopy 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 on flame emission spectroscopy, an instrumental method that identifies metal ions from their line spectra.
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Topic overview
Flame emission spectroscopy is an instrumental method for analysing metal ions in solution. This is a Triple-only topic.
The sample is put into a flame, and the light given out is passed through a spectroscope. The output is a line spectrum, and the pattern of lines identifies which metal ions are present. The intensity of the lines shows their concentration.
Instrumental methods have three advantages over chemical tests: they are more accurate, more sensitive so they detect tiny amounts, and much faster. Unlike flame tests, they can also identify several different metal ions in the same sample without the colours masking each other.
Revision notes
How it works
The sample is put into a flame and the light given out is passed through a spectroscope.
The output is a line spectrum. The pattern of lines is characteristic of a particular metal ion, and the intensity of the lines indicates its concentration.
Advantages of instrumental methods
More accurate than chemical tests. More sensitive, so they detect very small amounts.
Much faster, and they can analyse several ions in one sample. This is why they are used in industry and in forensic analysis.
Comparison with flame tests
In a flame test, mixtures cause colours to mask each other, particularly sodium's strong yellow.
Flame emission spectroscopy avoids this because each metal ion produces its own distinct pattern of lines, which can be identified even in a mixture.
Key points
- The sample is put into a flame.
- The light passes through a spectroscope.
- The output is a line spectrum.
- The line pattern identifies the metal ion.
- Line intensity shows concentration.
- Instrumental methods are accurate, sensitive and fast.
Worked examples
Example 1
Describe how flame emission spectroscopy is carried out. [2 marks]
Model answer
The sample is put into a flame (1 mark), and the light given out is passed through a spectroscope to produce a line spectrum (1 mark).
Example 2
Give three advantages of instrumental methods over chemical tests. [3 marks]
Model answer
They are more accurate (1 mark). They are more sensitive, so they can detect very small amounts (1 mark). They are much faster (1 mark).
Example 3
Explain why flame emission spectroscopy is more useful than a flame test for a mixture of metal ions. [2 marks]
Model answer
In a flame test the colours of different ions can mask each other (1 mark), whereas each metal ion produces its own distinct pattern of lines in a spectrum, so several can be identified in the same sample (1 mark).
Common mistakes
Saying the output is a colour.
It is a line spectrum, with a characteristic pattern of lines.
Giving only one advantage.
Accuracy, sensitivity and speed are all examinable.
Forgetting that intensity indicates concentration.
The lines identify the ion; their intensity gives the amount.
Confusing it with a flame test.
A flame test is a chemical test observed by eye; this is an instrumental method.
Exam tips
- Learn the three advantages as a set.
- Say line spectrum, not colour.
- Explain the mixture advantage over flame tests.
- Remember this is a Triple-only topic.
Key terms
- Flame emission spectroscopy
- An instrumental method identifying metal ions in solution.
- Line spectrum
- The pattern of lines produced, characteristic of an ion.
- Spectroscope
- The instrument that produces the spectrum.
- Sensitive
- Able to detect very small amounts.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.