What is the Difference Between Sulfuric Acid and Sulfurous Acid?

The key difference between sulfuric acid and sulfurous acid lies in the oxidation number of sulfur and their acidity. Here are the main differences between the two:

1. Oxidation Number of Sulfur: Sulfuric acid (H2SO4) has an oxidation number of +6 for sulfur, while sulfurous acid (H2SO3) has an oxidation number of +4 for sulfur.
2. Acidity: Sulfuric acid is a very strong diprotic acid, meaning it yields two protons (H+) per atom when it dissociates in water. In contrast, sulfurous acid is a relatively weak acid.
3. Structure and Formation: Sulfuric acid is formed by the combination of sulfur, oxygen, and water vapor, and it is produced by burning elemental sulfur and then reacting the resulting sulfur dioxide with water. Sulfurous acid, on the other hand, forms when sulfur dioxide dissolves in water.
4. Physical Properties: Sulfuric acid is a dense, oily, and colorless liquid with a molecular weight of 98.07 g/mol and a density of 1.84 g/cm³. Sulfurous acid is a clear, colorless, and weak acid with a pungent, burning sulfur odor.
5. Stability: Sulfurous acid is less stable than sulfuric acid and decomposes into its chemical constituents quickly since it is thermodynamically unstable.
6. Uses: Sulfuric acid is used in various industrial processes, such as the production of fertilizers, dyes, explosives, and batteries. Sulfurous acid is used as a reducing agent and as a disinfectant, as are solutions of bisulfite and sulfite salts.

Comparative Table: Sulfuric Acid vs Sulfurous Acid

Here is a table that highlights the differences between sulfuric acid (H2SO4) and sulfurous acid (H2SO3):

The key difference between sulfuric acid and sulfurous acid lies in the oxidation number of sulfur and their acid strength. Sulfuric acid is a strong diprotic mineral acid, while sulfurous acid is a weak acid.