Characteristic Reactions of Aluminum Ions (Al³⁺)

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Page ID: 97259

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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 \(\ce{Al^{3+}}\):

Aqueous Ammonia:

Aluminum ion reacts with aqueous ammonia to produce a white gelatinous precipitate of Al(OH)3:

\[\ce{Al^{3+}(aq) + 3NH3(aq) + 3H2O(aq) <=> Al(OH)3(s) + 3NH4+(aq)} \nonumber \]

Sodium Hydroxide

A strong base, such as \(\ce{NaOH}\), precipitates \(\ce{Al(OH)3}\), which is amphoteric and dissolves in an excess of hydroxide or in acids.

\[\ce{Al^{3+}(aq) + 3OH^-(aq) <=> Al(OH)3(s)} \nonumber \]

\[\ce{Al(OH)3(s) + OH-(aq) <=> Al(OH)4-(aq)} \nonumber \]

\[\ce{Al(OH)3(s) + 3H+(aq) <=> Al3+(aq) + 3H2O(l)} \nonumber \]

Aluminon

The dye aluminon is adsorbed by the gelatinous \(\ce{Al(OH)3}\) 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 \(\ce{Al^{3+}}\) after precipitation of \(\ce{Al(OH)3}\) with aqueous ammonia.

No Reaction

\(\ce{Cl^-}\), \(\ce{SO_4^{2-}}\)