Acid Ionization Fractional Ionization of a Monoprotic Weak Acid Weak acids are those that are not leveled, or completely ionized in the solvent. One common weak acid in aqueous solution is acetic acid, CH 3 CO 2 H. Solutions of this acid are found in the household under the name vinegar. Chemists commonly abbreviate acetic acid using the symbolic formula, HOAc .
Acetic acid is a relatively weak acid.
The degree of ionization in aqueous solution depends on the formal concentration of HOAc , as well as the existence of other acid or base species that may be in solution. However, the formal concentration does not change since we have a fixed number of formula weights HOAc per liter of solution. These are the only two forms of acetic acid we have to consider for moderately weak pure aqueous solutions. If we divide both sides by volume, and use the definition of formal which is a mathematical statement of mass balance, i.e., the sum of the molar concentrations of all acetic species equals the formula weights we put into solution. Calculation of the fraction of species in a particular form is easy if we know the pH or similarly, the proton concentration, and the dissociation constant.