Potassium oxide

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

Potassium oxide

Names
IUPAC name potassium oxide
Systematic IUPAC name potassium oxidopotassium
Other names potash, dipotassium oxide
Identifiers
CAS Number	12136-45-7 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:88321
ChemSpider	23354117 Y
ECHA InfoCard	100.032.012
EC Number	235-227-6
MeSH	Potassium+oxide
PubChem CID	25520
UNII	58D606078H Y
UN number	2033
CompTox Dashboard (EPA)	DTXSID3049754
InChI InChI=1S/2K.O N Key: NOTVAPJNGZMVSD-UHFFFAOYSA-N N
SMILES O([K])[K]
Properties
Chemical formula	K2O
Molar mass	94.196 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]
Solubility in water	Reacts[1] forming KOH
Solubility	Soluble in diethyl ether[2]
Structure
Crystal structure	Antifluorite cubic, cF12[3]
Space group	Fm3m, No. 225[3]
Lattice constant	a = 6.436 Å[3] α = 90°, β = 90°, γ = 90°
Coordination geometry	Tetrahedral (K+) Cubic (O2−)
Thermochemistry
Heat capacity (C)	83.62 J/mol·K[4]
Std molar entropy (S⦵298)	94.03 J/mol·K[4]
Std enthalpy of formation (ΔfH⦵298)	−363.17 kJ/mol[1][4]
Gibbs free energy (ΔfG⦵)	−322.1 kJ/mol[1]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Corrosive, reacts violently with water
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
NFPA 704 (fire diamond)	3 0 1 W
Safety data sheet (SDS)	ICSC 0769
Related compounds
Other anions	Potassium sulfide Potassium selenide Potassium telluride Potassium polonide
Other cations	Lithium oxide Sodium oxide Rubidium oxide Caesium oxide
Related potassium oxides	Potassium peroxide Potassium superoxide Potassium ozonide
Related compounds	Potassium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Production

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]

${\displaystyle {\ce {K2O2 + 2 K -> 2 K2O}}}$

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

${\displaystyle {\ce {2KNO3 + 10K -> 6K2O + N2 (^)}}}$

Other possibility is to heat potassium peroxide at 500 °C which decomposes at that temperature giving pure potassium oxide and oxygen.

${\displaystyle {\ce {2K2O2 -> 2K2O + O2 (^)}}}$

Potassium hydroxide cannot be further dehydrated to the oxide but it can react with molten potassium to produce it, releasing hydrogen as a byproduct.

${\displaystyle {\ce {2KOH + 2K <=> 2K2O + H2 (^)}}}$

Properties and reactions

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.

Term use in industry

The chemical formula K₂O (or simply 'K') is used in several industrial contexts: the N-P-K numbers for fertilizers, in cement formulas, and in glassmaking formulas. Potassium oxide is often not used directly in these products, but the amount of potassium is reported in terms of the K₂O equivalent for whatever type of potash was used, such as potassium carbonate. For example, potassium oxide is about 83% potassium by weight, while potassium chloride is only 52%. 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 18.8%.

References

1. Anatolievich, Kiper Ruslan. "potassium oxide". chemister.ru. Retrieved 2014-07-04.
2. 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. Wyckoff, Ralph W.G. (1935). The Structure of Crystals (2nd ed.). Reinhold Publishing Corp. p. 25. {{cite book}}: |work= ignored (help)
4. Dipotassium oxide in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD) (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 oxide, sulfide, selenide und telluride des lithiums, natriums und kaliums". Zeitschrift für Elektrochemie und Angewandte Physikalische Chemie. 40 (8): 588–93. doi:10.1002/bbpc.19340400811.
7. Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.

External links