Acids

Acid, any material that in liquid suspension perceives sour, changes the color of certain symbols(e.g., reddens blue litmus paper), reacts with some metals (e.g., iron) to release hydrogen, reacts with bases to form salts, and advances certain chemical reactions (acid catalysis). Examples of acids include the inorganic matters known as the mineral acids—sulfuric, nitric, hydrochloric, and phosphoric acids—and the organic compounds belonging to the carboxylic acid, sulfonic acid, and phenol groups. The before-mentioned substances restrain one or more hydrogen atoms that, in solution, are released as positively charged hydrogen ions (see Arrhenius theory).