2.45 - 2.46 Up in flames
Fireworks produce a whole range of different colours. All fireworks release energy in the form of heat energy and are therefore exothermic. Explosions and rocket power is provided by gunpowder and similar explosive mixtures.
Colours are achieved by mixing compounds which contain various metal ions into the explosive. When hot, these metal ions produce light of specific colours. The colour produced by a particular metal ion can be used in the laboratory as way of identifying the metal ion present in a compound.
Assumed background knowledge
2.45. Activity 1
Students should:
- 2.45 describe how to carry out a flame test
2.46 Activity 2. Colour coding - to learn
Students should:
- 2.46 know the colours formed in flame tests for the cations: lithium, sodium, potassium, calcium, copper
| Use the two images to match the metal to the colour. Make a copy of the blank table. Use your own words to describe each of the flame colours and write your descriptions in the appropriate column. |
2.47 Activity. Testing for some other Cations:
Students should:
- 2.47 describe tests for these cations: Ammonium, Copper II, Iron II and Iron III.
Use the video find out the results obtained when sodium hydroxide solution is added to solutions containing either ammonium (NH4+) ions, Copper (II) ions (Cu2+), Iron II ions (Fe2+) or iron III ions (Fe3+) . Add your results to a copy of the table
2.48 Activity. Testing for anions: Carbonate ions
Students should:
- 2.48 describe tests for these anions: chloride, bromide, iodide, sulfate and carbonate
The test for carbonate ions is to add an acid to the unknown substance. Bubbles of carbon dioxide will be formed if a carbonate is present.
The equation below is for the reaction of sodium carbonate with sulfuric acid.
2.48 Activity. Testing for anions: Sulfate ions
The insolubility of barium sulfate is why barium ions are used to test unknown solutions for the presence of sulfate ions. Acidified barium sulfate solution is added to the unknown solution.
A white precipitate indicates the presence of sulfate.
2.48 Activity. Testing for anions: chloride, bromide and iodide ions
Acidified silver nitrate solution is added to the unknown solution. A precipitate forms if chloride, bromide or iodide are present.
This test for chloride ions bromide and iodide ions uses the fact that silver chloride , silver bromide and silver iodide are all insoluble in water.
Silver chloride is white, silver bromide is cream and silver iodide is yellow.
Ammonia solution will dissolve silver chloride but not silver iodide.