Qualitative Analysis
Qualitative analysis is chemical analysis designed to identify the components of a substance or mixture,
e.g. identifying the cations and anions in an ionic compound.
Al3+ and Pb2+ have the same observations with both aqueous sodium hydroxide and aqueous ammonia.
To distinguish between these two cations, add a few drops of potassium iodide (sodium iodide can also
be used) to the solution which contains either of these two cations.
If Pb2+ ion is present, a bright yellow precipitate will form as lead (II) iodide is formed.
Equation: Pb2+(aq) + 2I-(aq)
PbI2(s)
If Al3+ is present, then, no precipitate will form.
NB: If the solution contains K+, Na+ or NH+4 ions, no precipitate will form with aqueous sodium hydroxide
or aqueous ammonia as these ions form soluble salts.