Characteristic Reactions of Antimony Ions (Sb³⁺)

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Most common oxidation states: +3, +5
M.P. 630º
B.P. 1380º
Density 6.69 g/cm³
Characteristics: Antimony is brittle and silvery. Not very active, but reacts with oxygen, sulfur and chlorine at high temperatures.
Characteristic reactions of \(\ce{Sb^{3+}}\): (Sb(III) is the more stable oxidation state.)

Chloride Ion:

No reaction observable, but will be present as \(\ce{SbCl4}\).

Aqueous Ammonia:

Sb(III) reacts with aqueous ammonia to precipitate white \(\ce{Sb(OH)3}\).

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

Sodium Hydroxide

Sodium hydroxide also precipitates \(\ce{Sb(OH)3}\), which is amphoteric and dissolves in an excess of hydroxide and in acids.

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

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

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

Hydrogen Sulfide

Under moderately acidic conditions, \(\ce{H2S}\) precipitates red \(\ce{Sb2S3}\).

\[\ce{2SbCl4(aq) + 3H2S(aq) <=> Sb2S3(s) + 6H+(aq) + 8Cl(aq)} \nonumber \]

This sulfide is soluble in solutions of hot \(\ce{NaOH}\) which contain excess sulfide ion and in hot, concentrated (12 M) \(\ce{HCl}\).

\[\ce{Sb2S3(s) + 3S2^{-}(aq) <=> 2SbS33(aq)} \nonumber \]

\[\ce{Sb2S3(s) + 6H^{+}(aq) + 8Cl^{-}(aq) <=> 2SbCl4^{2-}(aq) + 3H2S(aq)} \nonumber \]

Water

Solutions of antimony(III) chloride in \(\ce{HCl}\) react when added to excess water to form the basic, white, insoluble salt \(\ce{SbOCl}\).

\[\ce{SbCl4^{-}(aq) + H2O(l) <=> SbOCl(s) + 2H^{+}(aq) + 3Cl^{-}(aq)} \nonumber \]

Reducing Agents

In the presence of \(\ce{HCl}\), either aluminum or iron will reduce \(\ce{Sb^{3+}}\) to \(\ce{Sb}\) metal, which will be deposited as black particles.

\[\ce{SbCl4^{-} (aq) + Al(s) <=> Sb(s) + Al^{3+}(aq) + 4Cl^{-}(aq)} \nonumber \]

No Reaction

\(\ce{SO4^{2-}}\)