Potassium oxide
Potassium oxide (KO) 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 KO. Production. Potassium oxide is produced from the reaction of oxygen and potassium; this reaction affords potassium peroxide, KO. Treatment of the peroxide with potassium produces the oxide: Alternatively and more conveniently, KO is synthesized by heating potassium nitrate with metallic potassium: Other possibility  is to heat potassium peroxide at 500 °C which decomposes at that temperature giving pure potassium oxide and oxygen. 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. KO crystallises in the antifluorite structure. In this motif the positions of the anions and cations are reversed relative to their positions in CaF, with potassium ions coordinated to 4 oxide ions and oxide ions coordinated to 8 potassium. KO 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 KO (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 KO 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%.