Flame tests and flame emission spectroscopy

In a nutshell

Metal ions (not the metal itself) can be identified using flame tests. This is because different metal ions produce different colours. They can also be identified using flame emission spectroscopy.

Flame test colours

Ion	Colour of flame
Lithium	Crimson red
Sodium	Yellow
Potassium	Lilac
Calcium	Orangey-red
Copper	Green

The flame test can only be used if a single metal ion is present.

procedure

1.	Clean a platinum wired loop by dipping it into dilute HCl.
2.	Hold loop in a blue flame of a Bunsen burner until it burns without colour.
3.	Dip the loop into the sample you want to test and put it in the flame.
4.	Record flame colour.
5.	Determine metal ion by using the table above.

Flame emission spectroscopy

Instrumental analysis methods such as flame emission spectroscopy can be used to identify a mixture of metal ions present in a solution. It can also be used to determine the concentration of the metal ion(s) present.

Procedure

1.	Place sample in a flame.
2.	Ions heat up leading to excited electrons.
3.	Electrons drop back to their original energy level and energy is transferred as light.
4.	Light passes through a spectroscope.
5.	Spectroscope detects the different wavelengths of light (different colours) which produces a line spectrum.
6.	Colours seen are dependant on the ionic charge and electron configuration.
7.	No ion has the same charge and same electron configuration as another, therefore each metal ion produces a different pattern of wavelengths (colours) so produces a different line spectrum.
8.	Concentration of a given ion can be determined by the intensity of the wavelength.

Example

Let's say you have a sample and you obtain the first spectrum below. You can then compare the spectrum to references. In this example the sample contains ion A and ion B as the wavelengths for the sample correspond to that of ions A and B.

Chemistry; Separate chemistry 2; KS4 Year 10; Flame tests and flame emission spectroscopy

Advantages of instrumental analysis

Very fast
Highly sensitive
Super accurate