Chemical tests
Flame (Cation) Tests
Gas Tests
Anion Tests
O2, Vital for living beings, flammable
CO2 , Poisonous, non-flammable
H2, Great source of fuel, explosive
NH3, Used to make fertilizers, smelly and poisonous
Cl2, many industrial uses, poisonous
Will turn colorless limewater cloudy
Will put out a lit splint
Will relight a blown out splint
Will explode with a squeaky pop if exposed to a lit splint
Damp litmus paper turns blue
Damp universal indicator / litmus paper will turn red and then bleaches. It has a dangerous but distinct smell.
Procedure
4) Observe colour of flame
3) Place the splint at the edge of a Bunsen Burner with a Blue
flame
2) Place salt/solution on splint
1) Coat a clean splint with water to prevent it from burning up
Why do different metal cations give different colours in a flame test?
The color of the light depends on the energies of the photons emitted, which are in turn are determined by the energies required to move electrons from one orbital to another.
Iron and magnesium do not burn in any particular colour. They can be determined with other tests.
Hydroxide (Cation) Test
Uses Sodium Hydroxide
Fe 2+ → forms a green precipitate
Fe 3+ → forms a brown precipitate
Cu2+ → forms a blue precipitate
NH4+ → forms ammonia gas (NH3 [see Gas Tests subsection for test])
Carbonate Ion tests
Halide tests
Sulphate tests
Test For Cl-, Br- & I-
1) Add acidified silver nitrate (the acid reacts with any other ions which could also give a precipitate)
2) Record the colour of the precipitate (it will be a silver halide)
Cl- > white, Br- > cream, I- > yellow
1) add dilute hydrochloric acid to the sample
2) add a few drops of dilute barium chloride solution
3) A white precipitate forms if sulfate ions are present.
1) Add hydrochloric acid to the solution, CO2 will be produced
2) Use Limewater to test for CO2 (see Gas Tests subsection for test)
Lithium is red
Sodium is yellow
Potassium is lilac
Calcium is orange
Copper is Blue Green
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