Carbonic acid (H2CO3) is a weak acid, not a strong acid. It only partially dissociates in water, releasing limited hydrogen ions (H+), unlike strong acids such as hydrochloric acid (HCl) or sulfuric acid (H2SO4), which completely dissociate. The acid dissociation constant (Ka) for carbonic acid is about 4.2 × 10^-7, which is much lower than the Ka for strong acids, confirming its weak acidic nature.
Explanation
- Carbonic acid forms when carbon dioxide dissolves in water, and it exists in equilibrium with water and CO2.
- It is considered a dibasic acid because it can release two protons in two steps, but each step is partial and reversible.
- The strength of an acid depends on its ability to ionize completely in solution. Carbonic acid ionizes partially, so it produces fewer hydrogen ions compared to strong acids.
- Strong acids have Ka values much greater than 1, while carbonic acid's Ka is significantly less, indicating weakness.
Thus, carbonic acid is classified as a weak acid.
