Potassium oxide
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224321639
2008-07-08T09:48:55Z
Axiosaurus
3399137
/* Properties and reactions */ corrected my mistake
{{Chembox new
| Name = Potassium oxide
| ImageFile = Potassium-oxide-3D-vdW.png
| ImageSize = 200px
| ImageName = Potassium oxide
| IUPACName = Potassium oxide
| OtherNames = Potassium monoxide
| Section1 = {{Chembox Identifiers
| CASNo = 12136-45-7
}}
| Section2 = {{Chembox Properties
| Formula = K<sub>2</sub>O
| MolarMass = 94.196 g/mol
| Appearance = gray crystalline solid
| Density = 2.35 g/cm<sup>3</sup>
| Solubility = Decomposes violently,<br />forming [[Potassium hydroxide|KOH]]
| MeltingPt = >490 °C <!--Holleman and Wiberg-->, (Decomposes at 350°C in [K<sub>2</sub>O<sub>2</sub>] and [K] form)
| BoilingPt = n/a
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Potassium superoxide]]<br />[[Potassium peroxide]]
| OtherCations = [[Lithium oxide]]</br>[[Sodium oxide]]
}}
}}
'''Potassium oxide''' is a [[Chemical compound|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 K<sub>2</sub>O.
==Production==
Potassium oxide is produced from the reaction of oxygen and potassium; this reaction affords [[potassium peroxide]], K<sub>2</sub>O<sub>2</sub>. Treatment of the peroxide with potassium produces the oxide:<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref>
: K<sub>2</sub>O<sub>2</sub> + 2 K → 2 K<sub>2</sub>O
Alternatively and more conveniently, K<sub>2</sub>O is synthesized by heating [[potassium nitrate]] with metallic potassium:
:2 KNO<sub>3</sub> + 10 K → 6 K<sub>2</sub>O + N<sub>2</sub>
[[Potassium hydroxide]] cannot be further dehydrated to the oxide.
==Properties and reactions==
K<sub>2</sub>O crystallises in the antifluorite structure. In this motif the positions of the [[anion]]s and [[cation]]s are reversed relative to their positions in [[calcium fluoride|CaF<sub>2</sub>]], with potassium ions coordinated to 4 oxide ions and oxide ions coordinated to 8 potassium.<ref>Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref> K<sub>2</sub>O 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 K<sub>2</sub>O is used in the N-P-K (nitrogen-phosphorus-potassium) numbers on the labels of [[fertilizer]]s. Although K<sub>2</sub>O 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 K<sub>2</sub>O 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==
<references/>
''Lange's Handbook of Chemistry (14th Edition)'', McGraw-Hill, 1992; Section 1; Table 1.15<br />
''The Condensed Chemical Dictionary (10th Edition)'', Gesner G. Hawley<br />
''Handbook of Preparative Inorganic Chemistry: Volume 1 (2nd Edition)'', Georg Brauer, 1963<br />
http://scifun.chem.wisc.edu/CHEMWEEK/AgriFert/agrifert.html<br />
http://www.inchem.org/documents/icsc/icsc/eics0769.htm<br />
http://www.webelements.com/webelements/compounds/text/K/K2O1-12136457.html</br>
[[Category:Oxides]]
[[Category:Potassium compounds]]
[[Category:Deliquescent substances]]
[[ca:Òxid de potassi]]
[[de:Kaliumoxid]]
[[it:Ossido di potassio]]
[[lv:Kālija oksīds]]
[[nl:Kaliumoxide]]
[[ja:酸化カリウム]]
[[pl:Tlenek potasu]]
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[[sv:Kaliumoxid]]
[[zh:氧化鉀]]