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Chemical Analysis
Flame Tests
We perform a flame test by putting a small amount of a compound to be
tested in a platinum wire loop which has been dipped in hydrochloric acid,
and then we hold the substance over a blue Bunsen flame
...
However when more NaOH is
added the aluminium will dissolve
...
Ammonium ions react with NaOH to form
ammonia and water:

NH4+ (aq) + OH- (aq) NH3 (aq) + H2O (l)
To test for ammonium ions, we add NaOH to a solution of an unknown
substance
...

When we warm the solution, ammonia is then given off as a gas
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Testing for Negative Ions

Testing for carbonates: If we add a dilute acid (e
...
hydrochloric) to a
carbonate, it fizzes and produces carbon dioxide gas
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For example, copper carbonate is a green
substance which when heated decomposes to give black copper oxide and
carbon dioxide
...
These two reactions
are shown below:

CuCO3 (s) → CuO (s) + CO2 (g)
ZnCO3 (s) → ZnO (s) + CO2 (g)
Testing for halides: When we add dilute nitric acid and silver nitrate solution
to an unknown solution, the appearance of a precipitate tells us what halide
ion is present
...
The ionic
equation for this is, where X- is the halide ion:

Ag+ (aq) + X- (aq) → AgX (s)
Testing for sulphates: Adding hydrochloric acid followed by a barium
chloride solution to sulphate ions in solution produces a white precipitate
(barium sulphate, an insoluble salt)
...
We add sodium hydroxide to a solution of the
unknown substance and gently warm it
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This reduces the nitrate ions to ammonium ions
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This is detected using damp red litmus which will turn blue
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It is the basis for detecting C=C bonds in
unsaturated oils and fats

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