An acid is a substance that can donate protons (H⁺ ions) or accept electron pairs in a chemical reaction. Acids are characterized by certain properties, including a sour taste, the ability to conduct electricity when dissolved in water, and the capacity to react with bases to form salts and water in a neutralization reaction.
In terms of their classification:
-
Arrhenius Acid: A substance that increases the concentration of hydrogen ions (H⁺) in aqueous solution. For example, hydrochloric acid (HCl) dissociates in water to produce H⁺ ions.
-
Brønsted-Lowry Acid: A substance that donates a proton (H⁺) to another substance. For example, in the reaction between acetic acid (CH₃COOH) and water, acetic acid donates a proton to water, making it a Brønsted-Lowry acid.
-
Lewis Acid: A substance that can accept an electron pair to form a covalent bond. This definition broadens the concept of acids to include compounds like aluminum chloride (AlCl₃) that act as acids without releasing protons.
Common examples of acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and citric acid (found in citrus fruits). Acids play essential roles in various chemical processes, biological functions, and industrial applications.