Potassium oxide 224729 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]] [[sr:Калијум оксид]] [[sv:Kaliumoxid]] [[zh:氧化鉀]]