Potassium oxide

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Potassium oxide
Potassium oxide
IUPAC name Potassium oxide
Other names Potassium monoxide
Identifiers
CAS number [12136-45-7]
Properties
Molecular formula K2O
Molar mass 94.196 g/mol
Appearance gray crystalline solid
Density 2.35 g/cm3
Melting point

>490 °C , (Decomposes at 350°C in [K2O2] and [K] form)
Boiling point

n/a
Solubility in water Decomposes violently,
forming KOH
Related compounds
Other anions Potassium superoxide
Potassium peroxide
Other cations Lithium oxide
Sodium oxide
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and 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.

Contents

[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

Potassium oxide adopts the structure seen for antifluorite. It 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

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

Lange's Handbook of Chemistry (14th Edition), McGraw-Hill, 1992; Section 1; Table 1.15
The Condensed Chemical Dictionary (10th Edition), Gesner G. Hawley
Handbook of Preparative Inorganic Chemistry: Volume 1 (2nd Edition), Georg Brauer, 1963
http://scifun.chem.wisc.edu/CHEMWEEK/AgriFert/agrifert.html
http://www.inchem.org/documents/icsc/icsc/eics0769.htm
http://www.webelements.com/webelements/compounds/text/K/K2O1-12136457.html