Chemical formula: H2SO4), the most important oxyacid of sulfur. Anhydrous sulfuric acid is a colorless oily liquid which crystallizes at 10.36 ° C. It is usually used in various aqueous solutions of various concentrations and is prepared by a tower method and a contact method. The former is obtained as crude dilute sulfuric acid, and the mass fraction is generally about 75%; the latter can obtain pure concentrated sulfuric acid with a mass fraction of 98.3%, a boiling point of 338 ° C, and a relative density of 1.84.

Sulfuric acid is one of the most active binary inorganic strong acids that react with many metals. High concentration of sulfuric acid has strong water absorption and can be used as a dehydrating agent for carbonized wood, paper, cotton and linen, and biological skin. When mixed with water, it also releases a lot of heat. It has strong corrosive and oxidizing properties and should be used with caution. It is an important industrial raw material that can be used in the manufacture of fertilizers, drugs, explosives, pigments, detergents, batteries, etc. It is also widely used in industries such as petroleum purification, metal smelting and dyes. Often used as a chemical reagent, it can be used as a dehydrating agent and a sulfonating agent in organic synthesis.

Pure sulfuric acid is generally a colorless oily liquid with a density of 1.84 g/cm3 and a boiling point of 337 ° C. It can be mutually soluble in water at any ratio, and a large amount of heat is released to boil the water. When heated to 290 ° C, sulfur trioxide began to be released, eventually becoming an aqueous solution of 98.54%, boiling at 317 ° C to become an azeotrope. The higher boiling point and viscosity of sulfuric acid are due to the stronger hydrogen bonds inside the molecule. Since sulfuric acid has a high dielectric constant, it is a good solvent for electrolytes, and a non-electrolyte solvent is not preferable. The melting point of sulfuric acid is 10.371 ° C. Adding water or adding sulfur trioxide will lower the freezing point.