Cation Lab Manual
Test For Cations
Cations (postively charged ions)
are usually identified using two main reagents:
In qualitative analysis, a cation
is usually detected by adding aqueous sodium hydroxide
or aqueous ammonia to the unknown solution. The colour
of precipitate and the reaction of the precipitate formed
in excess of alkali added are important for the identification
of cation species.
table shows that most hydroxides are soluble except
for Group I metal hydroxides e.g. NaOH, KOH and Ca(OH)2,
All other metal ions react with
hydroxide ions in solution to form insoluble hydroxides.
The chemical reaction involved in the formation of the
insoluble metal hydroxide is called precipitation.
Solubility is very important
in order to understand precipitation.