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Cation Lab Manual
2. Aqueous ammonia
Ammonia dissolves in water and dissociates
partially to form hydroxide ions:
NH3 (g) + H2O
(l) ----> NH4+ (aq) + OH-
(aq)
A few drops of aqueous ammonia is
usually added to a 2 cm3 portion of the sample
salt solution and then to excess or until no further
change is observed
a) Most metal ions (except sodium,
potassium and calcium) react with aqueous
ammonia to form insoluble hydroxides.
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Al3+ (aq) ion
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| Add
dilute NH3 (aq) until no further change
is observed. |
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| Observation |
White precipitate,
insoluble in excess |
| Name and formula
of precipitate |
Aluminium hydroxide,
Al(OH)3 |
| Type of chemical
reaction(s) |
Precipitation of
Al(OH)3 |
| Ionic equation |
Al3+ (aq)
+ 3OH- (aq) ---> Al(OH)3 (s) |
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