Manganese, Mn²⁺

Most common oxidation states: +2, +7; +3, +4, and +6 also exist.

M.P. 1244^o

B.P. 1962^o

Density 7.43 g/cm³

Characteristics: 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 Mn(OH)₂:

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:

Hydrogen Peroxide:

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

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

MnO₂(s) + H₂O₂(aq) + 2H⁺(aq) --> Mn²⁺(aq) + O₂(g) + 2H₂O(l)

Sodium Bismuthate:

Solid sodium bismuthate oxidizes Mn²⁺ to purple MnO₄^- without heating. With heating, the product is MnO₂.

 No Reaction:

Cl^-, SO₄^2-

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