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| Potassium oxide | |
|---|---|
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| 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 references |
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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 |
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.
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] 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.
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%.
References
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
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
Wikipedia content modification information:
- This page was last modified on 8 July 2008, at 09:48.
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