acides

Acids (acides in French) are substances that release protons in aqueous solution or, more broadly, accept electron pairs in chemical reactions. In the Arrhenius sense, acids increase the concentration of H+ in water and typically produce species such as HCl or H2SO4. The Bronsted-Lowry definition broadens this to any species that donate a proton to a base, while Lewis acids are substances that accept an electron pair. Acids can be classified by strength (strong versus weak) and by the number of protons they can donate (monoprotic versus polyprotic).

Common properties include a sour taste in safe contexts, the ability to turn blue litmus red, and a tendency to react with carbonates to release CO2. In aqueous solutions, a low pH indicates higher acidity. Acids can corrode metals and are reactive with many substances; safe handling requires appropriate protective measures. In organic chemistry, carboxylic acids, phenols, and related functional groups contribute acidity through stabilization of the conjugate base.

Applications span industry and biology. Mineral acids such as hydrochloric, sulfuric, and nitric acids are used in chemical synthesis, metal processing, and energy storage. Organic acids occur in metabolism, food, and beverages, and contribute flavors and preservation properties. In biology, amino acids and other biomolecules contain acidic groups essential for structure and function. The study of acids underpins pH measurement, buffering, and acid–base titrations, and has a rich historical lineage from Arrhenius definitions to the broader Bronsted-Lowry and Lewis theories.

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