Many practical problems relating to environmental and physiological chemistry involve solutions containing more than one acid.
In this section, we will restrict ourselves to a much simpler case of two acids, with a view toward showing the general method of approaching such problems by starting with charge- and mass-balance equations and making simplifying assumptions when justified.
In general, the hydrogen ions produced by the stronger acid will tend to suppress dissociation of the weaker one, and both will tend to suppress the dissociation of water, thus reducing the sources of H+ that must be dealt with.
Consider a mixture of two weak acids HX and HY; their respective nominal concentrations and equilibrium constants are denoted by Cx , Cy , Kx and Ky ,
Starting with the charge balance expression