Flame Tests (Oxford AQA IGCSE Chemistry)
Revision Note
Written by: Alexandra Brennan
Reviewed by: Stewart Hird
Required Practical: Flame Tests
Objective
To identify the metal ion in an unknown compound using flame testing techniques.
Apparatus
Bunsen burner
Test tubes and test tube rack
Nichrome wire mounted in a handle
Samples of known metal chloride solutions:
Lithium chloride
Sodium chloride
Potassium chloride
Calcium chloride
Copper chloride
Salt solution labelled unknown
Method
Add 1 cm3 of each chloride solution into five separate test tubes
Dip the wire into the first solution
Hold the tip of the wire into a blue Bunsen burner flame
Record the observed colour change
Clean the wire and repeat for the other four solutions
Carrying out a flame test
Practical Tip
It is really important you clean the wire with dilute acid in between each test otherwise the colours could mask one another.
Results
Record your results for each test carefully in a suitable table like the one below:
Sample | Colour of flame |
|---|---|
Lithium chloride | |
Sodium chloride | |
Potassium chloride | |
Calcium chloride | |
Copper chloride | |
Unknown |
Evaluation
Once you have recorded the results from the tests you performed, use them to identify the positive metal ion in the unknown solution.
Worked Example
A student was given five samples labelled A-E.
The following set of results were obtained from carrying out a flame test on the samples.
Use the results to identity the positive metal ion in each one.
Sample | Colour of flame | Identity of ion |
|---|---|---|
A | lilac | |
B | yellow | |
C | crimson | |
D | green | |
E | red |
Answer:
The identities of the ion in each sample are:
A: Potassium, K+
B: Sodium, Na+
C: Lithium, Li+
D: Barium, Ba2+
E: Calcium, Ca2+
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