I read somewhere that: "During the course of a titration, an acid in solution reacts with a base in solution, and when a strong acid or strong base is involved, this reaction always goes to completion...." HA(aq) + OH- (aq) → A- (aq) + H2O (1)" "At the equivalence point (which is the place where moles of acid = moles of base) the titration is complete, no HA remains; and the only substances in the beaker are water, the conjugate base, A-, and a spectator ion. The end point is the place at which the indicator changes color. The endpoint and the equivalence point are not always identical, but they are always very close." "Halfway to the end point, half of the HA has reacted to become its conjugate base A- and water. At that point, the concentrations of HA and A- are equal. When these concentrations are equal, log [A-]/[HA] is zero and pH = pKa (see equation 4). It is clear then that pKa can be read directly from the titration curve as the pH at the half-way point of a titration." So I understand most all of this, but one thing is bugging me: Why does [HA]=[A-] halfway to the end point? Shouldn't the concentrations be equal to one another the whole time b/c they are both in the same volume of container and dissociate with the same molar ratio 1:1? I must be totally misunderstanding something b/c that makes no sense to me.