WHAT CAUSES THE BRIGHT COLORS IN FIREWORKS?
Mystery Metal and flame test
Flame tests are useful in lab. situations when it is necessary to identify a compound that is an unknown. This happens frequently when labels fall off of containers. Many fireworks get their colour because salts burn brightly. Copper salts give fireworks green colour and lithium aand strontium produce red colours.
Material
Fume cupboard; Bunsen burner and bench protection sheet
- 2 crucibles, containing unknown, labelled A & B
- 5 crucibles, each containing a different metal compounds,
- flame test wires with cork holders
- 2M hydrochloric acid (corrosive)
- calcium chloride (irritant)
- copper chloride (toxic)
- strontium chloride (irritant)
- sodium chloride
- potassium chloride
WEAR SAFETY GLASSES ALL THE TIME; TURN ON EXHAUST FANS
Procedure (teacher's demo for Yr4 students)
- Light the Bunsen burner.
Adjust it to get a roaring flame.
- Dip the flame test wire
into the concentrated acid, then hold it in the hottest part of the flame.
Repeat the process until there is little or no colour from the test wire in
the flame. Let it cool. You may have to repeat this step several times
especially towards the end of the experiment.
- Take one of the crucibles
containing a known metal compound. Now pick up the flame test wire. Dip
the tip of the wire into a little concentrated hydrochloric acid. Then
touch the compound in the crucible with the tip so that a tiny bit of the
powder sticks to it.
- Hold the wire in the flame
of the Bunsen burner so that the powdered solid is in the edge of the
flame. You should see a coloured flame. Write down the colour in the table
below.
- Now repeat instructions 2 to 4 with the other four compounds. Write down the flame colour for each metal in the table.
-
OBSERVE & RECORD
RESULTS
|
Name of Metal Salt Used
|
Colour of Flame
|
|
Sodium Chloride
|
|
|
Potassium Chloride
|
|
|
Calcium Chloride
|
|
|
Copper Chloride (or
sulphate)
|
|
|
Strontium Chloride
|
|
- Now you are ready to help Sherlock Holmes identify the substances. Take one of the unknown substances, then do the flame test on it and see if you can tell which metal is in it from the colour of the flame.
Test of the unknown
|
UNKNOWN #
|
COLOUR OF FLAME OBSERVED
|
METAL ion in the salt
|
|
A
|
|
|
|
B
|
|
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