Potassium oxide
IUPAC name Potassium oxide
Other names Potassium monoxide Potash
Identifiers
CAS number	12136-45-7 Y
UN number	2033
Properties
Molecular formula	K2O
Molar mass	94.20 g/mol
Appearance	pale yellow solid
Density	2.35 g/cm3
Melting point	>350 °C decomp.
Solubility in water	Reacts forming KOH
Structure
Crystal structure	Antifluorite (cubic), cF12
Space group	Fm3m, No. 225
Coordination geometry	Tetrahedral (K+); cubic (O2–)
Thermochemistry
Std enthalpy of formation ΔfHo298	−361 kJ·mol−1[1]
Standard molar entropy So298	98 J·mol−1·K−1[1]
Hazards
MSDS	ICSC 0769
EU Index	Not listed
Main hazards	Corrosive, reacts violently with water
Flash point	Non-flammable
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
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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[link]

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:^[2]

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.

Potassium oxide can also be made by heating potassium metabisulfite crystals above 180°C:

K₂S₂O₅ → K₂O + 2SO₂

Properties and reactions[link]

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.^[3][4] 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.

Fertilizers[link]

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[link]