Characteristic Reactions of Strontium Ions (Sr²⁺)

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Most common oxidation state: +2
M.P. 770º
B.P. 1380º
Density 2.60 g/cm³
Characteristics: Strontium is an active metal, very similar to barium and calcium.

Characteristic reactions of Sr²⁺

Sulfate Ion

Soluble sulfates, including sulfuric acid, precipitate white \(\ce{SrSO4}\):

\[\ce{Sr^{2+}(aq) + SO4^{2-}(aq) <=> SrSO4(s) } \nonumber \]

Chromate Ion

Although chromate ion does not give a precipitate in neutral or acid solutions of \(\ce{Sr^{2+}}\), yellow \(\ce{SrCrO4}\) precipitates from slightly basic solution:

\[\ce{Sr^{2+}(aq) + CrO4^{2-}(aq) <=> SrCrO4(s)} \nonumber \]

Strontium chromate dissolves readily in acids, even in acetic acid. It is only slightly soluble in alcohol or alcohol-water mixtures.

Oxalate Ion

Oxalate ion precipitates white \(\ce{SrC2O4}\):

\[\ce{Sr^{2+}(aq) + C2O4^{2-}(aq) <=> SrC2O4(s)} \nonumber \]

Strontium oxalate is insoluble in acetic acid, but soluble in mineral acids such as \(\ce{HCl}\):

\[\ce{SrC2O4(s) + 2H^{+}(aq) <=> Sr^{2+}(aq) + H2C2O4(aq) } \nonumber \]

Ammonium Carbonate

Ammonium carbonate precipitates white \(\ce{SrCO3}\).

\[\ce{Sr^{2+}(aq) + CO3^{2-}(aq) <=> SrCO3(s)} \nonumber \]

Aqueous ammonia should also be added to ensure complete precipitation. The aqueous ammonia assures that the concentration of carbonate ion will be high enough by preventing the hydrolysis of carbonate ion to form hydrogen carbonate ion:

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

\[\ce{CO3^{2-}(aq) + H2O(l) <=> HCO3^{-}(aq) + OH^{-}(aq)} \nonumber \]

Strontium carbonate is soluble in acid, including dilute acetic acid, in strong bases, and in aqueous ammonia.

No Reaction

\(\ce{Cl^{-}}\), \(\ce{NH3(aq)}\), \(\ce{OH^{-}}\)