Why does the concentration of fuming sulfuric acid exceed 100%?

The concentration of fuming sulfuric acid is chemically expressed in terms of the SO3 content. When sulfuric acid contains a high proportion of SO3, its concentration can exceed 100%. This is because SO3 is a gas with strong hygroscopic properties; when it absorbs moisture, it combines with water molecules to form sulfuric acid molecules, releasing a large amount of heat in the process. Therefore, when moisture in the air comes into contact with fuming sulfuric acid, water molecules react with SO3 to form more sulfuric acid molecules, thereby causing the concentration to exceed 100%. The concentration of a substance can exceed 100% because the definition of concentration refers to the amount of substance per unit volume or mass. When certain substances are present in a solution or mixture, their concentration relative to the total volume or mass of the solution or mixture can exceed 100%. This mainly occurs in compounds containing hygroscopic substances, such as fuming sulfuric acid. The concentration of fuming sulfuric acid can be calculated through experimental methods; a common approach is to determine the content of SO3 in fuming sulfuric acid using titration. First, fuming sulfuric acid is dissolved in water to prepare a solution, then an alkaline solution is used as a titrant to titrate it to the neutral point, with an indicator being used to indicate the endpoint. By determining the required volume through titration and using the reaction equation, the content of SO3 can be calculated, thereby obtaining the concentration of fuming sulfuric acid. .