Potassium oxide

Potassium oxide

Names
IUPAC name Potassium oxide
Systematic IUPAC name Potassium oxidopotassium
Other names Dipotassium monoxide, Potash
Identifiers
CAS Number	12136-45-7 N
ChemSpider	23354117 N
EC Number	235-227-6
Jmol 3D model	Interactive image
MeSH	Potassium+oxide
UNII	58D606078H N
InChI InChI=1S/2K.O N Key: NOTVAPJNGZMVSD-UHFFFAOYSA-N N
SMILES O([K])[K]
Properties
Chemical formula	K2O
Molar mass	94.20 g·mol−1
Appearance	Pale yellow solid
Odor	Odorless
Density	2.32 g/cm3 (20 °C) 2.13 g/cm3 (24 °C)
Melting point	740 °C (1,360 °F; 1,010 K) decomposes from 300 °C
Solubility in water	Reacts forming KOH
Solubility	Soluble in EtOH, ether
Structure
Crystal structure	Antifluorite cubic, cF12
Space group	Fm3m, No. 225
Lattice constant	a = 6.436 Å α = 90°, β = 90°, γ = 90°
Coordination geometry	Tetrahedral (K+) Cubic (O2−)
Thermochemistry
Specific heat capacity (C)	83.62 J/mol·K
Std molar entropy (So298)	94.03 J/mol·K
Std enthalpy of formation (ΔfHo298)	−363.17 kJ/mol
Gibbs free energy (ΔfG˚)	−322.1 kJ/mol
Vapor pressure	{{{value}}}
Related compounds
Other anions	Potassium sulfide
Other cations	Lithium oxide Sodium oxide Rubidium oxide Caesium oxide
Related potassium oxides	Potassium peroxide Potassium superoxide
Related compounds	Potassium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Potassium oxide (K₂O) is an ionic compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive compound. Some materials of commerce, 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 oxide, K₂O. Treatment of the peroxide with potassium produces the oxide:

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 but it can react with molten potassium to produce it, releasing hydrogen as a byproduct.

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. Although K₂O is the correct formula for potassium oxide, potassium oxide is not used directly in these products. Normally potassium carbonate or some other potassium compound is used. 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%.