A solution of the primary standard potassium hydrogen phthalate, KHC8H4O4, was prepared by dissolving 0.4877 g of potassium hydrogen phthalate in about 50 mL of water. Titration with a KOH solution required 24.71 mL to reach a phenolphthalein end point. What is the molarity of the KOH solution?

Answer 1

The titration is a 1:1 titration of KHP and KOH.
KOH + KHP ==> H2O + K2P

mols KHP = grams/molar mass
mols KOH = mols KHP (look at the coefficients in the balanced equation; they are 1:1)
M KOH = mols KOH/L KOH