Acid

Article

January 20, 2022

Acid (acid from Latin acidus / acēre meaning acid) is one of the basic categories of chemical compounds. Acid is a chemical substance whose aqueous solutions have a characteristic acidic taste, the ability to turn blue litmus into red, the ability to react with bases and certain metals (such as calcium) to form salts. Aqueous acid solutions have a pH value of less than 7. Non-aqueous acids are usually formed when an anion (negative ion) reacts with one or more positively charged hydrogen cations. The lower the pH value, the higher the acidity, and therefore the higher the concentration of positive hydrogen ions in the solution. Chemicals or substances that have acidic properties are said to be acidic. There are three widely accepted definitions of acid: the Arrhenius definition, the Bransted-Laurie definition, and the Lewis definition. Arrhenius' definition formulates acids as substances that increase the concentration of hydrogen ions (H +), or more precisely, hydronium ions (H3O +), when dissolved in water. The Bronsted-Lori definition is expansion: an acid is a substance that can act as a proton donor. By that definition, any compound that can be easily deprotonated can be considered an acid. Examples include alcohols and amines containing O-H or N-H fragments. Lewis acid is a substance that can receive a pair of electrons and form a covalent bond. Examples of Lewis acids include all metal cations, and electron-deficient molecules such as boron trifluoride and aluminum trichloride. Examples of known acids are hydrochloric acid (a solution of hydrochloric acid, which is present in gastric acid in the stomach, where it activates digestive enzymes), acetic acid (vinegar is a dilute solution of this liquid), sulfuric acid (used in car batteries), and tartaric acid solid material used in baking). As these examples show, acids can be solutions or pure substances, and can be derived from solids, liquids or gases. Strong acids and some concentrated weak acids are corrosive, although there are exceptions such as carborans and boric acid. Definitions and Concepts Modern definitions �

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