Acids are substances that release hydrogen ions (H⁺) when dissolved in aqueous solution. These free H⁺ ions, also called protons, are responsible for the sour taste, corrosiveness, and reactivity associated with acidic substances.
In water, H⁺ ions often associate with water molecules to form hydronium ions (H₃O⁺).
Examples of common acids:
- Hydrochloric acid (HCl) → H⁺ + Cl⁻
- Sulfuric acid (H₂SO₄) → 2H⁺ + SO₄²⁻
- Acetic acid (CH₃COOH) → H⁺ + CH₃COO⁻
The strength of an acid depends on how completely it dissociates in water:
- Strong acids (e.g., HCl) fully dissociate.
- Weak acids (e.g., acetic acid) only partially dissociate.
Acids play crucial roles in digestion, industry, chemistry labs, and environmental processes, and their reactivity with bases forms the foundation of neutralization reactions.