(8) How much KOH must be added to reach the equivalence point?
At the equivalence point, the potassium hydroxide will have reacted with all of the
hydrofluoric acid. In other words, the number of mmol of KOH added at the equivalence point is equal to the original number of mmol of HF. The initial number of mmol of HF is 4.0 mmol. 4.0 mmol of KOH is present in 40.0 mL of .1M KOH solution. Therefore, the equivalence point will be reached after an addition of 40.0 mL. In titrations of 5.0 mL each, the equivalence point will be reached in eight titrations.
(9) What is the pH at the equivalence point?
The expected pH is greater than 7, implying that a concentration of hydroxide ions has accumulated. The reaction of the HF with the KOH creates fluoride ions, which in turn react with the water according to
