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

The Group 1 elements in the periodic table are known as the alkali metals. They include lithium, sodium and potassium, which all react vigorously with air and water.

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 alkali metal ion is present in the compound.

Flame colours and the alkali metal ion they represent

Flame colourIon present
RedLithium, Li+
OrangeSodium, Na+
LilacPotassium , K+
Brick redCalcium, Ca2+