Flame tests for metal ions

There are several different tests to detect and identify the ions in compounds. It is important that the test for any ion is unique. The results of a test must let you determine which ion is present, rather than being uncertain about which ion it is.

Flame tests

Different metal ions produce different flame colours when they are heated strongly. This is the basis of flame tests. To carry out a flame test:

  • dip a clean wire loop into a solid sample of the compound being tested
  • put the loop into the edge of the blue flame from a Bunsen burner
  • observe and record the flame colour produced
A sample is held in a Bunsen burner flame and burns red.Carrying out a flame test

The table shows the flame test colours for six common metal ions.

Ion presentFlame test colour
Lithium, Li+Red
Sodium, Na+Yellow
Potassium, K+Lilac
Calcium, Ca2+Orange-red
Barium, Ba2+Green
Copper, Cu2+Blue-green
Question

A sample of an ionic compound produces an orange-red flame test colour. Identify the metal ion present.

The metal ion is calcium, Ca2+.

curriculum-key-fact
Each metal ion produces a different flame test colour.