Potassium oxide

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Potassium oxide
Potassium oxide spacefilling model
Identifiers
CAS number 12136-45-7 YesY
ChemSpider 23354117 YesY
UNII 58D606078H N
EC-number 235-227-6
MeSH Potassium+oxide
Jmol-3D images Image 1
Properties
Molecular formula K2O
Molar mass 94.20 g mol−1
Appearance Pale yellow solid
Odor Odorless
Density 2.32 g/cm3 (20 °C)[1]
2.13 g/cm3 (24 °C)[2]
Melting point 740 °C (1,360 °F; 1,010 K) [2]
decomposes from 300 °C[1]
Solubility in water Reacts[1] forming KOH
Solubility Soluble in EtOH, ether[2]
Structure
Crystal structure Antifluorite cubic, cF12[3]
Space group Fm3m, No. 225[3]
Lattice constant a = 6.436 Å[3]
Lattice constant α = 90°, β = 90°, γ = 90°
Coordination
geometry
Tetrahedral (K+)
Cubic (O2–)
Thermochemistry
Specific
heat capacity
C
83.62 J/mol·K[4]
Std molar
entropy
So298
94.03 J/mol·K[4]
Std enthalpy of
formation
ΔfHo298
−363.17 kJ/mol[1][4]
Gibbs free energy ΔG −322.1 kJ/mol[1]
Hazards
MSDS ICSC 0769
Main hazards Corrosive, reacts violently with water
Related compounds
Other anions Potassium sulfide
Other cations Lithium oxide
Sodium oxide
Rubidium oxide
Caesium oxide
Related potassium oxides Potassium peroxide
Potassium superoxide
Related compounds Potassium hydroxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Potassium oxide (K2O) is an ionic compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive compound. Some materials of commerce, such as fertilizers and cements, are assayed assuming the percent composition that would be equivalent to K2O.

Production[edit]

Potassium oxide is produced from the reaction of oxygen and potassium; this reaction affords potassium peroxide, K2O2. Treatment of the peroxide with potassium produces the oxide:[5]

K2O2 + 2 K → 2 K2O

Alternatively and more conveniently, K2O is synthesized by heating potassium nitrate with metallic potassium:

2 KNO3 + 10 K → 6 K2O + N2

Potassium hydroxide cannot be further dehydrated to the oxide.

Properties and reactions[edit]

K2O crystallises in the antifluorite structure. In this motif the positions of the anions and cations are reversed relative to their positions in CaF2, with potassium ions coordinated to 4 oxide ions and oxide ions coordinated to 8 potassium.[6][7] K2O is a basic oxide and reacts with water violently to produce the caustic potassium hydroxide. It is deliquescent and will absorb water from the atmosphere, initiating this vigorous reaction.

Fertilizers[edit]

The chemical formula K2O is used in the N-P-K (nitrogen-phosphorus-potassium) numbers on the labels of fertilizers. Although K2O is the correct formula for potassium oxide, potassium oxide is not used as a fertilizer in these products. Normally, potassium chloride, potassium sulfate, or potassium carbonate is used as a fertilizer source for potassium. The percentage of K2O given on the label only represents the amount of potassium in the fertilizer if it was in the form of potassium oxide. Potassium oxide is about 83% potassium by weight, but potassium chloride, for instance, is only 60% potassium by weight. Potassium chloride provides less potassium than an equal amount of potassium oxide. Thus, if a fertilizer is 30% potassium chloride by weight, its standard potassium rating, based on potassium oxide, would be only 21.7%.

References[edit]

  1. ^ a b c d e Anatolievich, Kiper Ruslan. "potassium oxide". http://chemister.ru. Retrieved 2014-07-04. 
  2. ^ a b c Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0. 
  3. ^ a b c Wyckoff, Ralph W.G. (1935). "The Structure of Crystals". American Chemical Society (2nd ed.) (Reinhold Publishing Corp.). p. 25. 
  4. ^ a b c Dipotassium oxide in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-07-04)
  5. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  6. ^ Zintl, E.; Harder, A.; Dauth B. (1934). "Gitterstruktur der oxyde, sulfide, selenide und telluride des lithiums, natriums und kaliums". Zeitschrift für Elektrochemie und Angewandte Physikalische Chemie 40: 588–93. 
  7. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.

External links[edit]