Equivalence point
The equivalence point in an acid-base titration is the point at which a certain amount of acid or base is present with the equivalent amount of base or acid. In the equivalence point the following applies:
The rate of change of the pH value is at its maximum at the equivalence point ; the titration curve therefore describes a turning point here . However, there is also a turning point at the half-equivalence point, where the rate of change of the pH value is minimal. In addition, there are equivalence points, for example for redox titrations .
Comparison with neutral point
The amount of substance of the hydroxide ions / oxonium ions is initially undetermined. Only for the combination of strong acid / strong base the following applies approximately:
If strong acids and bases are titrated with one another, the equivalence point in aqueous solution is equal to the neutral point , the pH value is 7. If, however, acids and bases of different strengths are titrated with one another, the resulting solution is not neutral at the equivalence point. For example, if a weak acid (e.g. acetic acid, CH 3 COOH) is neutralized with the equivalent amount of a strong base, the pH is ultimately basic. This is because the acetate ions (CH 3 COO - ), which form the corresponding base of the weak acid CH 3 COOH, now act as a base themselves and are thus able to capture H + ions, i.e. with H. 2 O to react to CH 3 COOH and OH - . The pH value at the equivalence point does not necessarily correspond to 7 here.
Examples
- If you add 1 mole of hydrochloric acid (HCl) and sodium hydroxide (NaOH) each , you get a neutral saline solution .
- If 1 mole of acetic acid (CH 3 COOH) and sodium hydroxide (NaOH) are combined, the result is an alkaline sodium acetate solution .
See also: half-equivalence point
