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Sulfate Ion (SO₄²⁻)

  • Page ID
    97284
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    Acid Equilibria

    \[\ce{SO42-(aq)+ H2O(l) <=> HSO4-(aq) + OH-(aq)} \nonumber \]

    with \(K_b = 1 \times 10^{-12}\)

    \[\ce{HSO4-(aq) + H2O(l) <=> H2SO4(aq) + OH-(aq)} \nonumber \]

    with \(K_b = 1 \times 10^{-15}\)

    Sulfate ion is a very weak base, while \(\ce{HSO4^{-}}\) is a fairly strong acid, with \(K_a = 0.01\). On the other hand, \(\ce{H2SO4}\) is a very strong acid. Because it is such a weak base, sulfate ion undergoes negligible hydrolysis in aqueous solution.

    Solubility

    Most sulfates, including those of \(\ce{Na^{+}}\), \(\ce{K^{+}}\), and \(\ce{NH4^{+}}\), are soluble in water. Exceptions that are insoluble are white lead(II) sulfate and white barium sulfate:

    \[\ce{BaSO4(s) <=> Ba2+(aq) + SO42-(aq)} \nonumber \]

    with \(K_{sp} = 1.4 \times 10^{-8}\)

    \[\ce{PbSO4(s) <=> Pb2+(aq) + SO42-(aq)} \nonumber \]

    with \(K_{sp} = 1.1 \times 10^{-10}\)

    Formation of white \(\ce{BaSO4}\) upon addition of \(\ce{Ba^{2+}}\) to a solution of \(\ce{SO4^{2-}}\), even if it is acidic, is a reliable test for sulfate. Other insoluble sulfates are those of calcium, strontium, and mercury(I).

    Oxidation-Reduction:

    Sulfate is a very weak oxidizing agent. Since sulfur is in its maximum oxidation number in sulfate ion, this ion cannot act as a reducing agent.


    This page titled Sulfate Ion (SO₄²⁻) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by James P. Birk.

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