Flame colours of group 1 and 2 compounds

Group 1 and 2 compounds produce characteristic flame colours when heated. This is due to electron transitions within the metal atoms. When energy is absorbed from the flame, electrons move to higher energy levels. As they fall back to lower levels, they release energy as light with a specific wavelength, producing the characteristic colour.

Flame test procedure:

1. Mix a small amount of the compound with a few drops of hydrochloric acid.
2. Clean a platinum or nichrome wire by heating it in a hot Bunsen flame.
3. Dip the wire into the compound/acid mixture.
4. Hold the wire in a hot flame and observe the colour produced.

Flame colours for group 1 and 2 compounds:

Identifying ammonium ions

To confirm the presence of ammonium (NH₄⁺) ions:

1. Add sodium hydroxide solution dropwise to a sample containing ammonium ions. Gently warm the mixture. The hydroxide ions react with the ammonium ions to produce ammonia gas: OH^-_(aq) + NH₄⁺_(aq) ➔ NH_3(g) + H₂O_(l)

2. Moisten a piece of red litmus paper and hold over the test tube. The paper will turn blue if ammonia gas is present, thereby confirming that ammonium ions were originally present in the sample.

Alternatively, the presence of ammonia can be confirmed by its reaction with hydrogen chloride gas (from concentrated hydrochloric acid), forming white fumes of solid ammonium chloride:

NH_3(g) + HCl_(g) ➔ NH₄Cl_(s)