An acid is a substance that donates protons (H⁺ ions) in a chemical reaction. Acids have specific characteristics, including:
- Taste: They often have a sour taste (characteristic of substances like vinegar or citric acid).
- pH Level: Acids have a pH level of less than 7.
- Reactivity: They react with bases (alkalis) to form salts and water in a neutralization reaction.
- Corrosiveness: Many acids can be corrosive, meaning they can damage materials, including metals and organic tissue.
- Properties in Solution: When dissolved in water, acids release H⁺ ions; for example, hydrochloric acid (HCl) dissociates into H⁺ and Cl⁻ ions.
In terms of classification, acids can be divided into several categories:
- Strong Acids: Completely dissociate in water (e.g., hydrochloric acid (HCl), sulfuric acid (H₂SO₄)).
- Weak Acids: Partially dissociate in water (e.g., acetic acid (CH₃COOH), citric acid).
In addition to the Brønsted-Lowry definition (proton donor), acids can also be defined in the Lewis acid-base theory as electron pair acceptors.