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Characteristic Reactions of Manganese Ions (Mn²⁺)

  • Page ID
    97273
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    • Most common oxidation states: +2, +7; +3, +4, and +6 also exist.
    • M.P. 1244º
    • B.P. 1962º
    • Density 7.43 g/cm3
    • Characteristics: Manganese is a gray or reddish-white metal. Very hard and brittle. Very similar to iron in activity. Dissolves readily in dilute acids.

    Characteristic Reactions of Mn²⁺

    Aqueous Ammonia

    Addition of aqueous ammonia precipitates white \(\ce{Mn(OH)2}\):

    \[\ce{Mn^{2+}(aq) + 2NH3(aq) + 2H2O(l) <=> Mn(OH)2(s) + 2NH4^{+}(aq)} \nonumber \] Mn3.gif

    The precipitate does not dissolve in excess ammonia, but does dissolve in solutions containing ammonium salts. The precipitate is easily oxidized by atmospheric oxygen to form Mn(III) or Mn(IV), which turns the precipitate a brownish color.

    Sodium Hydroxide

    Sodium hydroxide precipitates manganese(II) hydroxide:

    \[\ce{Mn^{2+}(aq) + 2OH^{-}(aq) <=> Mn(OH)2(s) } \nonumber \] Mn4.gif

    Hydrogen Peroxide

    In basic solutions, \(\ce{H2O2}\) oxidizes Mn(II) to Mn(IV), giving a brown precipitate:

    \[\ce{Mn(OH)2(s) + H2O2(aq) -> MnO2(s) + 2H2O(l)} \nonumber \] Mn5a1.gif

    \(\ce{MnO2}\) is generally insoluble in acids, but does react with hot concentrated hydrochloric acid to release chlorine gas. In acid solution, \(\ce{H2O2}\) becomes a reducing agent, and the \(\ce{MnO2}\) will dissolve:

    \[\ce{MnO2(s) + H2O2(aq) + 2H^{+}(aq) -> Mn^{2+}(aq) + O2(g) + 2H2O(l)} \nonumber \]

    Mn5a2.gif

    Sodium Bismuthate

    Solid sodium bismuthate oxidizes \(\ce{Mn^{2+}}\) to purple \(\ce{MnO4^{-}}\) without heating. With heating, the product is \(\ce{MnO2}\).

    \[\ce{2Mn^{2+}(aq) + 5BiO3^{-}(aq) + 14H^{+}(aq) -> 2MnO4^{-}(aq) + 5BiO^{+}(aq) + 7H2O(l)} \nonumber \] Mn5b.gif

    No Reaction

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


    This page titled Characteristic Reactions of Manganese Ions (Mn²⁺) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by James P. Birk.