66One way to provide them is to apply the law of mass conservation in terms of the two "reagents"
H and A.
C stands for analytical concentration. In some texts one mass balance equation is replaced by an
equation of charge balance. This is satisfactory for simple cases like this one, but is more difficult
to apply to more complicated cases as those below.
Together with the equation defining Ka, there are now three equations in three unknowns. When
an acid is dissolved in water CA = CH = Ca, the concentration of the acid, so [A] = [H]. After some
further algebraic manipulation an equation in the hydrogen ion concentration may be obtained.