Definition

A weak acid is a Acide which does not dissociate completely in water: when a weak acid AH is put in the presence of Eau, the following reaction takes place:

$AH+H\_2O\; \backslash \; let\; us\; rightleftharpoons\; A^-\; +\; H\_3O^+$

The reaction total but is not balanced. (see the detailed articles Constante of balance and chemical equation), i.e. to have more substance of the right-sided of the reaction, it is necessary to add more product AH of the left side, it always remains of acid AH in solution. In an acid couple bases, a weak acid is associated with a strong base if the acid is really weak, i.e. for a pKa higher than 14 (or a weak base for a lower pKa) in which it changes after having yielded its H⁺ proton.

One classifies the weak acids according to their Constante of acidity, i.e. according to their capacity with more or less dissociating in the presence of water. It is estimated that an acid is weak when its PKa is higher than 0. An acid is all the more weak as its pKa is high. Its combined base is thus all the more strong and stable this same pKa is high.

Examples of weak acids

The hydrofluoric Acid , the Methanoic acid , the Ethanoic acid and the other carboxylic acids are weak acids.

See too

• Acid, bases

• weak Base
• pH
• Constante of balance
• Chemical reaction