Potassium oxide

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Potassium oxide

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MeSH	Potassium+oxide
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RTECS number	Template:Unbulleted list
UN number	2033
Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	Template:Chem molar mass
Appearance	Pale yellow solid
Odor	Odorless
Density	2.32 g/cm3 (20 °C) 2.13 g/cm3 (24 °C)
Melting point	Template:Chembox CalcTemperatures
Solubility	Soluble in diethyl ether
Template:Longitem	Antifluorite cubic, cF12
Template:Longitem	Fm3m, No. 225
Template:Longitem	a = 6.436 Å α = 90°, β = 90°, γ = 90°
Template:Longitem	Tetrahedral (K+) Cubic (O2−)
Template:Longitem	83.62 J/mol·K
Template:Longitem	94.03 J/mol·K
Template:Longitem	−363.17 kJ/mol
Template:Longitem	Potassium sulfide Potassium selenide Potassium telluride Potassium polonide
Template:Longitem	Lithium oxide Sodium oxide Rubidium oxide Caesium oxide
Template:Longitem	Potassium peroxide Potassium superoxide Potassium ozonide
Template:Longitem	Potassium hydroxide

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

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:

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Alternatively and more conveniently, K₂O is synthesized by heating potassium nitrate with metallic potassium:

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Other possibility is to heat potassium peroxide at 500 °C which decomposes at that temperature giving pure potassium oxide and oxygen.

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Potassium hydroxide cannot be further dehydrated to the oxide but it can react with molten potassium to produce it, releasing hydrogen as a byproduct.

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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. 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.

Term use in industry

The chemical formula K₂O (or simply 'K') is used in several industrial contexts: the N-P-K numbers for fertilizers, in cement formulas, and in glassmaking formulas. Potassium oxide is often not used directly in these products, but the amount of potassium is reported in terms of the K₂O equivalent for whatever type of potash was used, such as potassium carbonate. For example, potassium oxide is about 83% potassium by weight, while potassium chloride is only 52%. 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 18.8%.