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potassium sulfate[pə′tas·ē·əm ′səl‚fāt]
a salt; colorless crystals. Density, 2.66 g/cm3, melting point, 1074°C. Solubility, 11.1 g per 100 g H2O at 20°C (24.1 g at 100°C).
Potassium sulfate is a consituent of natural potassium salts, such as schoenite (K2SO4·MgS04·6H2O), from which it is also extracted. Potassium sulfate is used in the preparation of alum and potash. In agriculture, it serves as a concentrated chlorine-free potassium fertilizer, containing no less than 45–52 percent K2O, no more than 1 percent MgO, and no more than 10 percent moisture; it is applied primarily to the soil under chlorine-sensitive crops (potatoes, tobacco, flax, grapes, citrus fruits). The presence of the sulfate ion in the fertilizer has a favorable effect on the yield of crucifers (cabbage, rutabagas, turnips) and legumes, which require a large amount of sulfur.
Heating potassium sulfate with concentrated sulfuric acid forms the acid salt potassium hydrosulfate (bisulfate): K2SO4 + H2SO4 = 2KHS04. At temperatures above its melting point (210°C), potassium hydrosulfate is converted first to potassium pyrosulfate (2KHS04 = K2S207 + H20) and then to potassium sulfate and sulfuric anhydride (K2S2O7 = K2SO4 + SO3). This reaction is used for converting substances that are nearly insoluble in acids (for example, calcinated A12O3, Fe2O3, Cr03) into soluble sulfates. Potassium hydrosulfate is also used as a flux in metallurgy.