Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. However, hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids. Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H +) into the solution, which then accept electron pairs. An example is boron trifluoride (BF 3), whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH 3). The second category of acids are Lewis acids, which form a covalent bond with an electron pair. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid. As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Chemicals or substances having the property of an acid are said to be acidic.Ĭommon aqueous acids include hydrochloric acid (a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits).
A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute. The word acid is derived from the Latin acidus/acēre, meaning 'sour'. This aqueous solution of acid can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. Acids form aqueous solutions with a sour taste.This solution disassociates and forms H+ ions which combine with H2O molecule of water to form H3O(Hydronium ion). A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H +.Īqueous Arrhenius acids have characteristic properties which provide a practical description of an acid.
Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. In the special case of aqueous solutions, proton donors form the hydronium ion H 3O + and are known as Arrhenius acids. The first category of acids are the proton donors, or Brønsted–Lowry acids. An acid is a molecule or ion capable of either donating a proton (i.e., hydrogen ion, H +), known as a Brønsted–Lowry acid, or, capable of forming a covalent bond with an electron pair, known as a Lewis acid.
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