The clear ammonium sulphate crystals, which appear white when finely dispersed, dissolve well in water with a slightly acidic reaction. When heated to 235 °C, the ammonia gas is split off, forming ammonium hydrogen sulphate. On further heating above the decomposition point of 280 °C, the intermediate product also decomposes to ammonium disulfate (NH4)2S2O7. When mixed with nitrites, decomposition can be explosive.
Ammonium sulphate is formed when ammonia is introduced into sulphuric acid in a highly exothermic reaction. To prevent the reaction from being too violent, the sulphuric acid is diluted with water. At a sulphuric acid concentration of over 70%, so much heat is generated that the water evaporates on its own. After careful evaporation, the crystalline salt is obtained:
2 NH3 + H2SO4 → (NH4)2SO4
Ammonium sulphate is one of the most important salts for the production of fertilizers due to its nitrogen content. It is also used together with ammonium nitrate. Ammonium sulphate is approved as food additive E 517 for carriers. It is also suitable as a flame retardant in paper production or as a nutrient salt for the cultivation of microorganisms, for example yeast fungi.