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Potassium oxide
IUPAC name	Potassium oxide
Other names	Potassium monoxide
Identifiers
CAS number	12136-45-7
UN number	2033
Properties
Molecular formula	K2O
Molar mass	94.20 g/mol
Appearance	pale yellow solid
Density	2.35 g/cm3
Melting point	>490 °C decomp.
Solubility in water	Decomposes violently, forming KOH
Structure
Crystal structure	Antifluorite (cubic), cF12
Space group	Fm3m, No. 225
Coordination; geometry	Tetrahedral (K+); cubic (O2–)
Hazards
MSDS	ICSC 0769
EU Index	Not listed
Main hazards	Corrosive, reacts violently with water
Flash point	Non-flammable
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
	(what is this?) (verify); Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
	Infobox references

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

[edit] 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:^[1]

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.

[edit] 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.^[2]^[3] 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.

[edit] Potassium oxide in fertilizers

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 52% 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 19%.

[edit] References

^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
^ Zintl, E.; Harder, A.; Dauth B. (1934), "Gitterstruktur der oxyde, sulfide, selenide und telluride des lithiums, natriums und kaliums", Z. Elektrochem. Angew. Phys. Chem. 40: 588–93
^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.

[0] Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

[1] Zintl, E.; Harder, A.; Dauth B. (1934), "Gitterstruktur der oxyde, sulfide, selenide und telluride des lithiums, natriums und kaliums", Z. Elektrochem. Angew. Phys. Chem. 40: 588–93

[2] Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.

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Contents

[edit] Production

[edit] Properties and reactions

[edit] Potassium oxide in fertilizers

[edit] References