MANGANESE (III) OXIDE

Chemical properties

manganese(III) oxide is a black, lustrous powder, sometimes tinged brown. Very hard.decomposes at 1080℃. Soluble in cold hydrochloric acid; not soluble in nitric acid (decomposes), hot sulfuric acid; insoluble in water. Noncombustible.

manganese(III) oxide is obtained by igniting manganese(IV) oxide or a manganese(II) salt in air at 800°C. It reacts slowly with cold dilute acids to form manganese(III) salts. Manganese(III) oxide occurs in nature as braunite (3Mn2O3.MnSiO3 ) and the monohydrate (Mn2O 3.H2O) occurs in the mineral manganite. The manganese(III) oxide crystal lattice contains Mn3+ and O2– ions. With concentrated alkalis, it undergoes disproportionation to give manganese(II) and manganese(IV) ions.

The Uses of MANGANESE (III) OXIDE

Manganese(III) oxide is used to produce ceramic magnets and semiconductors. Further, it serves as a precursor to lithium manganese oxide. In addition to this, it acts as a useful battery cathode.

Preparation

Anhydrous manganese(III) oxide is found as the mineral braunite, Mn2O3, while a hydrated form, Mn2O3.H2O, which is chemically more reactive, occurs as manganite. Manganese forms both anions and cations in oxidation state +3. Simple salts of tervalent manganese are not stable. However, complexes are more stable, the hexacyanomanganates(III) being an example: K3Mn(CN)6 is a red crystalline solid, isomorphous with potassium hexacyanoferrate(III) and slowly hydrolysed.
Manganese(III) oxide is formed as a grey solid by heating manganese(IV) oxide to 700°C for several hours:
4MnO2 ---> 2Mn203 + O2
It is converted into trimanganese tetroxide when heated above 940°C in air or reduced by hydrogen above 230°C. Hot concentrated hydrochloric acid is oxidized to chlorine by manganese(III) oxide:
Mn203 (s) + 6H + + 2e- ==2Mn2+ + 3H2O
Mn203 (s) + 6H + + 2Cl- ---> 2Mn2+ + 3H2O + Cl2

Definition

In nature as manganite, a manganese ore.

Hazard

Flammable in finely divided form. Toxic by inhalation of dust.

Flammability and Explosibility

Not classified

Safety Profile

Moderately toxic by subcutaneous and intratracheal routes. See also MANGANESE COMPOUNDS.