Flame Tests

How to do a Flame Test

•Wear safety glasses and a labcoat and carry out in a fume cupboard.•Dip a clean nichrome metal wire into concentrated hydrochloric acid•Dip the wire into the solid sample (the acid converts it to a more volatile chloride)• Hold the wire at the top of a blue bunsen flame and observe the colourProblems:• intense colour of sodium impurities can mask other colours•describing colours is subjective
In group one, rubidium and caesium give red-violet and blue-violet flame colours respectively.From group two, barium gives a pale-green flame colour and calcium gives a brick-red flame colour.

What Causes Colours in Flame Tests

Electrons absorb heat energy from the flame and transition to a higher energy level or excited state. The electrons immediately fall back to their ground state emitting a photon of visible light of a frequency characteristic of the atom.The electron transition energies are related to the frequencies emitted by the equation E = hf where h is the Planck constant.The electron transition in sodium corresponds to a wavelength of 590nm (yellow).The electron transition in magnesium corresponds to a wavelength outside the visible spectrum (no flame colour).

Flame Test Colours

These colours are caused by excited electrons emitting visible light as they return to their ground state in the atoms.