Basic introduction of fuming sulfuric acid

Fuming sulfuric acid, that is, sulfuric acid solution of sulfur trioxide. Colorless to light brown viscous fuming liquid, its density, melting point and boiling point vary with SO3 content. When it is exposed to the air, the volatilized SO3 and the water vapor in the air form fine dew drops of sulfuric acid and smoke, so it is called fuming sulfuric acid.

Types of fuming sulfuric acid: including pyrosulfuric acid (H2S2O7), dimerized sulfuric acid (H4S2O8) tripolysulfuric acid (H6S3O12), and the like.

Basic traits: colorless or slightly colored thick liquid, capable of emitting asphyxiating sulfur trioxide fumes, which is a sulfuric acid containing excessive sulfur trioxide. 50% or more of sulfur trioxide containing cold crystals. Has a strong water absorption. When it is mixed with the aqueous phase, sulfur trioxide is combined with water to form sulfuric acid. The relative density is about 1.9 (including 20% sulfur trioxide). The freezing point varies greatly with concentration, showing a tendency to rise first and then fall. The freezing point of fuming sulfuric acid containing 20% free sulfur trioxide is 2.5 °C. With the increase of free sulfur trioxide content, when the free sulfur trioxide is 45%, the freezing point reaches 35.0 °C, and then the free sulfur trioxide content is gradually increased. The freezing point will decrease rapidly. Water, organic matter and oxidants are prone to explosions. Very corrosive.

Fuming sulfuric acid is a product in the process of producing sulfuric acid. It is unstable in nature and reacts with water to form sulfuric acid. Fuming sulfuric acid can be regarded as sulfuric acid with a concentration exceeding 100%, and SO3 is volatilized in the air to form an acid mist to emit smoke (as if more than 68% of nitric acid is called fuming nitric acid due to acid mist). Usually, the content of fuming sulfuric acid is calculated based on the sulfur trioxide content therein, for example, 20% fuming sulfuric acid means that 20% of its mass is sulfur trioxide. In H2SO4·xSO3, when x=1, it is pyrosulfuric acid. Generally, the mass fraction containing SO3 is 20%, 40%, 60%, 66%, and the like. If the concentration of sulfuric acid is converted to, the H2SO4 in fuming sulfuric acid can exceed 100%. Some people think that fuming sulfuric acid mainly contains pyrosulfuric acid (H2S2O7). Strong oxidizing and water absorbing, dehydrating and corrosive. Used in synthetic dyes, drugs. Fuming sulfuric acid is often used in sulfonation reactions, not only because of the high concentration, but also because the fuming sulfuric acid contains more electrophilic sulfur trioxide. In addition, it is also commonly used as a water absorption and dehydrating agent.

The composition of fuming sulfuric acid is complex. In addition to sulfuric acid and sulfur trioxide, there are also various types such as pyrosulfuric acid (H2S2O7), dimerized sulfuric acid (H4S2O8) tripolysulfuric acid (H6S3O12) and H4S3O15, H2S3O10, (H2SO4)20, etc. A sample of sulfuric acid polymer.