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In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base.It can be used to determine pH via titration.Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.
An example of this case would be the splitting of hydrochloric acid HCl in water. Since HCl is a strong acid (it splits up to a large extent), its conjugate base (Cl −) will be weak. Therefore, in this system, most H + will be hydronium ions H 3 O + instead of attached to Cl − anions and the conjugate bases will be weaker than water molecules.
In water, by altering the autoionization equilibrium, bases yield solutions in which the hydrogen ion activity is lower than it is in pure water, i.e., the water has a pH higher than 7.0 at standard conditions. A soluble base is called an alkali if it contains and releases OH − ions quantitatively.
The essence of Brønsted–Lowry theory is that an acid is only such in relation to a base, and vice versa. Water is amphoteric as it can act as an acid or as a base. In the image shown at the right one molecule of H 2 O acts as a base and gains H + to become H 3 O + while the other acts as an acid and loses H + to become OH −.
In practice, the mixture can be created by dissolving the acid in water, and adding the requisite amount of strong acid or base. When the pK a and analytical concentration of the acid are known, the extent of dissociation and pH of a solution of a monoprotic acid can be easily calculated using an ICE table.
When a solution of an acid, HA, is at equilibrium, by definition the concentrations are related by the expression [A −][H +] = K a [HA]; pK a = −log K a. The solvent (e.g. water) is omitted from the defining expression on the assumption that its concentration is very much greater than the concentration of dissolved acid, [H 2 O] ≫ T A ...
For example, anhydrous acetic acid (CH 3 COOH) as solvent is a weaker proton acceptor than water. Strong aqueous acids such as hydrochloric acid and perchloric acid are only partly dissociated in anhydrous acetic acid and their strengths are unequal; in fact perchloric acid is about 5000 times stronger than hydrochloric acid in this solvent. [3]
At equilibrium, the water contains a certain amount of alkalinity contributed by the concentration of weak acid anions. Conversely, the addition of acid converts weak acid anions to CO 2 and continuous addition of strong acids can cause the alkalinity to become less than zero. [12]