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History and Production
From Latin magnes, meaning magnet. In Italian manganese means corrupt form of magnesia. C.W. Scheele recognized the existence of a new element in the mineral pyrolusite (MnO2) in 1774. Subsequently, it was isolated by
J.G. Gahn by the reduction of manganese dioxide (MnO2) with charcoal (carbon) in the same year. High purity of the metal (99.9%) can now be produced by the electrolysis of aqueous manganese(II) sulfate. The metal can also be obtained by the reduction of the
oxide with sodium or magnesium metals. Manganese is used to produce alloys such as an additive to steel to improve hardness and as a scavnger so as to remove sulfur and oxygen in the steel. With aluminium, antimony and small amount of copper it forms highly ferromagnetic alloys.
The dioxide compound is used in dry cells while the permanganate (MnO4-) is used in medicine and in quantitative analysis.
Physical Data
It is gray-white in appearance, similar to iron but much harder. alpha-manganese is the most stable allotropic form while the gamma form, which changes slowly to the
alpha at room temperature, is believed to be soft and easily bent. Manganese is widely distributed in nature and found in a variety of minerals such as pyrolusite and
rhodochrosite, MnCO3.
Interatomic distance: 273.4 pm (gamma)
Melting point: 1246°C
Boiling point: 2061°C
Thermal conductivity/Wm-1K-1: 7.82 (27°C)
Density/kgm-3: 7440 (20°C)
Standard Thermodynamic Data (atomic gas)
Enthalpy of formation: 280.7 kJ/mol
Gibbs free energy of formation: 238.5 kJ/mol
Entropy: 173.7 J/mol K
Heat capacity: 20.8 J/mol K
Electronic data
Electronic configuration: [Ar] 3d5 4s2
Term symbol: 6S5/2
Electron affinity: not stable kJ/mol Electronegativity (Pauline): 1.55
Ionization energy (first, second, third): 717.274, 1509.03, 3248.47 kJ/mol
Chemical properties
Manganese is not readily attacked by air and only forms a nitride at red heat. However, it becomes reactive which burns in air if finely divided. It decomposes water to give hydrogen and readily reacts with
aqueous acids to form Mn(II) salts. With non-metallic elements it is usually not reactive at room temperature but can react
violently when heated.
Test for manganese:
(1) Manganese compounds give a violet borax bead when hot and red when cold in the oxidizing flame. In the reducing flame, there is no color.
(2) Fusion of a manganese compound with sodium carbonate and potassium nitrate on porcelain gives a green manganate, Mn(VI)O4.
Test for Mn2+ ions:
(1) Ammonium sulfide gives a flesh-colored precipitate of manganese(II) sulfide, readily soluble in dilute acids and in ethanoic acid (distinction from cobalt, nickel and zinc).
(2) If a manganese(II) salt is boiled with a strong oxidizing agent such as lead(IV) oxide and concentrated nitric acid, the purple color of the premanganate ion is seen.
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