H2SO3, known as sulfurous acid, is classified as a weak acid.
To understand why it’s considered weak, it’s important to look at its ionization in water. When H2SO3 is dissolved in water, it partially dissociates into H+ ions and HSO3– ions. This means that not all of the sulfurous acid molecules release protons, which is characteristic of weak acids.
In contrast, strong acids, like HCl or H2SO4, completely dissociate in water, releasing all their protons. Since H2SO3 does not do this, we categorize it as a weak acid. Additionally, it does not show the characteristics of a strong base either, as it does not accept protons readily or significantly increase hydroxide ion concentration in solution.
In summary, H2SO3 is a weak acid due to its incomplete dissociation in aqueous solution.