Testing for ions and gases

Chemists are often asked to test a sample of a substance to find out if it contains specific ions or compounds. There are a variety of techniques used to do this.

Testing for ions – flame tests

It is possible to use a flame test to detect the presence of an alkali metal ion.

A sample is held in a Bunsen burner flame and burns red.A cleaned, moistened flame test wire is dipped into a solid sample of the compound. It is then put into the edge of a blue Bunsen flame. The flame colour produced indicates which metal ion is present in the compound.

Flame colours and the metal ion they represent

Flame colourIon present
RedLithium, Li+
Yellow-orangeSodium, Na+
LilacPotassium, K+
Brick redCalcium, Ca2+
Apple greenBarium, Ba2+