The base ionization constant then gives the relation
Since must be equal to
Since all of the hydrofluoric acid has reacted at the equivalence point, the number of moles of fluoride ions is the same as the initial number of moles of hydrofluoric acid. The total volume at the equivalence point is 60.0 mL, yielding a molarity of
4.0 mmol/60.0 mL=.07 M for the fluoride ions. According to the equilibrium in equation (19), an amount x of the fluoride ions reacts with water to form hydroxide ions and hydrofluoric acid. Again, using equation (20) and the procedure for the dissociation of weak acids, x is found to be
