Name:______________________________
AP CHEMISTRY -- PROBLEM SET 6
6-1 An XX.X mL sample of a 0.100 M solution of a diprotic acid, H2A, is titrated with 0.100 M KOH.
For H2A, Ka1 = X.XX  10–5 and Ka2 = X.XX  10–10.
a) Calculate the concentration of A2– prior to the addition of any KOH.
b) What is the pH of the initial solution?
c) What is the pH exactly half way to the first equivalence point?
d) What is the pH exactly half way between the first and second equivalence points?
e) What is the pH at the second equivalence point?
6-2 The percentage by mass of nitric acid, HNO3, in a nitric acid solution is to be determined by titration
with NaOH solution.
a) Initially the NaOH solution was standardized by titration with a solution of potassium
acid phthalate, KHP, a monoprotic acid with a molecular weight of 204.2. A sample
of pure KHP weighing 1.XXX g was dissolved in water and titrated with NaOH solution.
To reach the equivalence point, 26.90 mL of base was required. What is the molarity of the base?
b) A 10.00 mL sample of the nitric acid solution was diluted with water to a total volume
of 500.0 mL. A 25.00 mL sample of the diluted acid solution was titrated with the
NaOH solution made in part (a). The equivalence point was reached after 2X.XX mL
of the base had been added. Calculate the molarity of the initial nitric acid solution.
6-3 For the compound H2XO2, K1 = X.XX  10–7 and K2 = X.XX  10–11.
a) For a 0.040 M H2XO2 solution,
[H+] =
[HXO2–] =
calculate the concentrations of:
[XO22–] =
b) Calculate the pH of a solution made from 0.100 moles of Na2XO2 in 1.00 L of water.
c) Sketch the titration curve which is expected when a solution
which contains 0.0100 moles of Na2XO2 and 0.0100 moles of
NaHXO2 is titrated with 0.XXX M HCl. Your sketch should
indicate the volumes of titrant needed to reach the equivalence points.
6-4 Aniline, C6H5NH2, is a weak base which is used extensively in the dye industry. Its conjugate acid,
aniline hydrochloride, [C6H5NH3]Cl, can be titrated by a strong base such as NaOH. Assume you titrate
25.0 mL of 0.100 M aniline hydrochloride with 0.115 M NaOH. Assume the Kb for aniline is X.XX  10–10.
a) What is the pH of the aniline hydrochloride solution before the titration begins?
b) What is the pH at the equivalence point?
c) What is the pH halfway to the equivalence point?
6-5 A solution is prepared by adding 0.0150 moles of NaX to 50.0 mL of 0.100 M HCl. This solution, which
still occupies 50.0 mL, has a pH of 4.XXX.
a) Calculate the concentrations of:
[H+] =
[X–] =
[HX] =
b) Determine the ionization constant for the acid HX.
c) Calculate the pH of this solution after 10.0 mL of 0.500 M NaOH has been added.
Assume the volumes are additive.