Flame emission spectroscopy

What you need to know

• Know the five required flame-test colours: lithium crimson, sodium yellow, potassium lilac, calcium orange-red and copper green.
• Instrumental methods can detect and identify elements and compounds and are accurate, sensitive and rapid.
• Flame emission spectroscopy produces a line spectrum that can be used to identify metal ions and measure their concentrations.
• Interpret flame-emission results by comparing the supplied result with a reference set presented in the same form.

The big picture

Flame tests can identify some metal ions because lithium, sodium, potassium, calcium and copper compounds produce distinctive flame colours. Flame emission spectroscopy is an instrumental method in which a sample is put into a flame and the emitted light is passed through a spectroscope to produce a line spectrum. The spectrum can be compared with reference data to identify metal ions and can also be used to measure their concentrations. Instrumental methods are accurate, sensitive and rapid, while mixtures can make simple flame tests harder because some flame colours may be masked.

From sample to spectrum

Follow what happens to the emitted light and what the result tells you.

1. 1

   Sample enters the flame

   In flame emission spectroscopy, the sample is put into a flame so that it gives out light.

2. 2

   Light reaches the spectroscope

   The emitted light is passed through a spectroscope so it can be analysed.

3. 3

   A line spectrum appears

   The instrument produces a line spectrum rather than relying only on the visible flame colour.

4. 4

   Compare with references

   The result can be interpreted by comparing it with an appropriate reference set presented in the same form.

5. 5

   Identify the ions

   Analysis of the line spectrum can reveal which metal ions are present in the solution.

6. 6

   Measure concentration

   The line spectrum can also be used to measure the concentrations of metal ions in the solution.

Five flame-test colours

Learn each ion and colour as one pair.

Interpret the result

Use only the supplied reference information.

An unknown solution produces a line spectrum that exactly matches Reference B. The supplied reference set labels B as calcium. What should you identify in the unknown?

Tap any cell to reveal it. Tap a column header to read one property down every item.

Spectroscopy essentials

Keep the method, output and interpretation vocabulary precise.

Memory hook

Crimson, Yellow, Lilac, Orange-red, Green: Li, Na, K, Ca, Cu — learn colour and ion as a pair.

Check yourself

Why can a mixture make a simple flame test less useful, and what kind of output does flame emission spectroscopy produce instead?