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Cation Lab Manual
1. Sodium hydroxide
An aqueous solution of sodium hydroxide
solution consists of mainly free, mobile sodium ions,
hydroxide ions and water molecules.
NaOH (aq) ----> Na+
(aq) + OH- (aq)
A few drops of sodium hydroxide
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) Adding NaOH (aq) to salt solutions
containing transition metal ions usually form coloured
precipitates while salt solutions containing Gp I, II
and III metal ions form white precipitates.
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Fe2+ (aq) ion
|
Ca2+ (aq) ion
|
| Add NaOH(aq) until
no further change is observed. |
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| Observation |
Dirty green precipitate
formed |
White precipitate
formed |
| Name and formula
of precipitate |
Iron(II) hydroxide,
Fe(OH)2 |
Calcium hydroxide,
Ca(OH)2 |
| Type of chemical
reaction |
Precipitation |
Precipitation |
| Ionic equation |
Fe2+ (aq)
+ 2OH- (aq)
-----> Fe(OH)2 (s) |
Ca2+ (aq)
+ 2OH- (aq)
-----> Ca(OH)2 (s) |
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