posted by Paul .
A student titrates 0.100M KOH into 50.00 ml of weak acid HX. The pH of the solution is 4.25 after 20.00 ml of the base has been added, and equivalence point is reached when 40.00 ml of the base is added.
1. What is the concentration of the acid, HX ?
2. What is the Ka value of acid HX?
HX + NaOH ==> NaX + H2O
1. mL x M = mL x M
2. 20 mL is at the half-way point to the equivalence point and pH = pKa; therefore, pKa = 4.25.