Aluminum, Al3+
Most common oxidation state: +3
M.P. 648o
B.P. 1800o
Density 2.70 g/cm3
Characteristics: Silvery, rather soft. Very active, but protected by an oxide coating.
Characteristic reactions of Al3+:
Aqueous Ammonia:
Aluminum ion reacts with aqueous ammonia to produce a white gelatinous precipitate of Al(OH)3:
Al3+(aq) + 3NH3(aq)+ 3H2O(aq) <==> Al(OH)3(s) + 3NH4+(aq)
Sodium Hydroxide:
A strong base, such as NaOH, precipitates Al(OH)3. This precipitate of Al(OH)3, which is amphoteric, dissolves in an excess of hydroxide or in acids.
Al3+(aq) + 3OH-(aq) <==> Al(OH)3(s)
Al(OH)3(s) + OH-(aq) <==> Al(OH)4-(aq)
Al(OH)3(s) + 3H+(aq) <==> Al3+(aq) + 3H2O(l)
Aluminon:
The dye aluminon is adsorbed by the gelatinous Al(OH)3 precipitate to form a red "lake" and a colorless solution. Although this reaction is not suitable for separation of aluminum ion, it can be used as a confirmatory test for Al3+ after precipitation of Al(OH)3 with aqueous ammonia.
No Reaction:
Cl-, SO42-