Sulfuric acid is strongly hygroscopic and attracts moisture from the air. When water is added to sulfuric acid, sulfuric acid compounds (“sulfuric acid hydrates”) are formed and no free oxonium ions. The resulting compound is strongly exothermic. Water poured on sulfuric acid becomes very hot and evaporates directly.
It is used for drying gases. Concentrated sulfuric acid destroys materials such as paper, wood, cotton, nylon, sugar, meat, etc., because it removes their water. Carbon remains, which can be seen by a black coloration.
Unfortunately, it is not possible to observe this principle when storing sulfuric acid. Therefore, the tank must be protected as efficiently as possible from water, or humidity.