Manganese(II) oxide

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Manganese(II) oxide
Manganese(II) oxide
Identifiers
CAS number 1344-43-0 YesY
PubChem 14940
RTECS number OP0900000
Properties
Molecular formula MnO
Molar mass 70.9374 g/mol
Appearance green crystals or powder
Density 5.43 g/cm3
Melting point 1,945 °C (3,533 °F; 2,218 K)
Solubility in water insoluble
Solubility soluble in acid
Refractive index (nD) 2.16
Structure
Crystal structure Halite (cubic), cF8
Space group Fm3m, No. 225
Coordination
geometry
Octahedral (Mn2+); octahedral (O2–)
Thermochemistry
Std molar
entropy
So298
60 J·mol−1·K−1[1]
Std enthalpy of
formation
ΔfHo298
−385 kJ·mol−1[1]
Hazards
EU Index Not listed
Flash point Non-flammable
Related compounds
Other anions Manganese difluoride
Manganese(II) sulfide
Other cations Iron(II) oxide
Related manganese oxides Manganese(II,III) oxide
Manganese(III) oxide
Manganese dioxide
Manganese heptoxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Manganese(II) oxide (systematically named manganese(2+) oxide(2−)) is an inorganic compound with chemical formula MnO.[2] It forms green crystals and is odorless. Manganese(II) oxide is the simplest ionic manganese oxide. Although it is classified as a very strong base, dissolved manganese(II) oxide is non-corrosive and does not attack the skin.

Chemical properties[edit]

Basicity[edit]

The oxide anion (O2−) in ionic manganese oxides such as manganese(II) oxide can assimilate a proton by recombination:

O2− + H+ → HO

Because of this capture of a proton (H+), manganese(II) oxide has basic character. In aqueous solution, it has a pKb value of ~−38. Oxide's conjugate acid is hydroxide (OH). A saturated solution has a near neutral pOH, indicating that most oxide ions are associated.

O2− + H2O is in a favored equilibrium with 2 HO

Structure[edit]

MnO has the NaCl, rock salt structure, where cations and anions are both octahedrally coordinated.[3] The composition of MnO can vary from MnO to MnO1.045.[3]
Below 118 K MnO is antiferromagnetic.[3] MnO has the distinction of being one of the first compounds[4] to have its magnetic structure determined by neutron diffraction in 1951.[5] This study showed that the Mn2+ ions form a face centered cubic magnetic sub-lattice where there are ferromagnetically coupled sheets which are anti-parallel with adjacent sheets.

Chemical reactions[edit]

Manganese(II) oxide undergoes the typical chemical reactions of an ionic manganese oxide. Upon treatment with a standard acid, it converts to a manganese(II) salt and water.[3] Oxidation of manganese(II) oxide gives manganese dioxide.

Preparation and occurrence[edit]

MnO can be prepared by the reduction of any higher oxide with hydrogen[3] e.g.:

MnO2 + H2 → MnO + H2O

Commercially it is prepared by reduction of MnO2 with hydrogen, carbon monoxide or methane:[2]

MnO2 + CO → MnO + CO2

MnO can also be prepared by heating MnCO3:[6]

MnCO3 → MnO + CO2

This calcining process is conducted anaerobically to prevent formation of Mn2O3. MnO occurs in nature as the rare mineral manganosite.

Applications[edit]

Together with manganese sulfate, MnO is a component of fertilizer and food additives. Many thousands of tons are consumed annually for this purpose.[2]

Other uses include: a catalyst in the manufacture of allyl alcohol, ceramics, paints, colored glass, bleaching tallow and textile printing.

References[edit]

  1. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X. 
  2. ^ a b c Arno H. Reidies "Manganese Compounds" Ullmann's Encyclopedia of Chemical Technology 2007; Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_123
  3. ^ a b c d e Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  4. ^ J.E Greedon, (1994), Magnetic oxides in Encyclopedia of Inorganic chemistry Ed. R. Bruce King, John Wiley & Sons ISBN 0-471-93620-0
  5. ^ Neutron Diffraction by Paramagnetic and Antiferromagnetic Substances C. G. Shull, W. A. Strauser, and E. O. Wollan, Phys. Rev. 83, 333 - 345 (1951), doi:10.1103/PhysRev.83.333
  6. ^ W.H. McCarroll (1994) Oxides- solid sate chemistry, Encyclopedia of Inorganic chemistry Ed. R. Bruce King, John Wiley & Sons ISBN 0-471-93620-0