General Definition of an Acid
An acid is a chemical substance that typically tastes sour, reacts with metals to produce hydrogen gas, and neutralizes bases. More formally, in an aqueous solution, acids increase the concentration of hydrogen ions (H⁺), or more accurately, hydronium ions (H₃O⁺). They are fundamental to many chemical and biological processes.
Key Principles: Brønsted-Lowry and Lewis Definitions
The Brønsted-Lowry definition states that an acid is a proton (H⁺ ion) donor. When an acid dissolves in water, it donates a proton to water, forming a hydronium ion. The more general Lewis definition identifies an acid as an electron-pair acceptor, which can include substances without hydrogen.
A Practical Example: Hydrochloric Acid
Hydrochloric acid (HCl) is a common example. In water, HCl dissociates into H⁺ and Cl⁻ ions. The H⁺ then combines with water (H₂O) to form H₃O⁺. This property makes hydrochloric acid a strong acid, widely used in industry and found in stomach acid to aid digestion.
Importance and Applications
Acids play vital roles in various applications, from industrial manufacturing (e.g., sulfuric acid in fertilizers) and food preservation (e.g., citric acid) to biological functions within living organisms. Understanding acids is crucial for fields like medicine, environmental science, and chemical engineering, affecting everything from blood pH regulation to battery function.