The fantasy

Water

We typically talk about acid-base reactions in aqueous-phase environments -- that is, in the presence of water. The most fundamental acid-base reaction is the dissociation of water:

H2O H+ + OH- In this reaction, water breaks apart to form a hydrogen ion (H+) and a hydroxide ion (OH-). In pure water, we can define a special equilibrium constant (Kw) as follows: KW = [H+][OH-] = 1.00x10-14 pH What is of interest in this reading, however, is the acid-base nature of a substance like water. Water actually behaves both like an acid and a base. The acidity or basicity of a substance is defined most typically by the pH value, defined as below: pH = -log[H+] pOH = -log[OH-]   Definitions of acids and bases Arrhenius acid: generates [H+] in solution base: generates [OH-] in solution normal Arrhenius equation: acid + base salt + water example: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) Brønsted-Lowery: acid: anything that donates a [H+] (proton donor) base: anything that accepts a [H+] (proton acceptor) normal Brønsted-Lowery equation: acid + base acid + base example: HNO2(aq) + H2O(aq) NO2-(aq)+ H3O+(aq) Lewis: acid: accepts an electron pair base: donates an electron pair Credit from www.shodor.org