AP Chemistry - Multiple Equilibria Test

For all problems below, show all work and be sure to use correct units and significant figures. Where a calculator function (such as solver) is used, be sure to show me exactly what was entered into the calculator, including the guess. No credit will be given for answers without work.

1. HA-1 is amphiteric. Kb = 2.1 x 10-9, Ka = 2.7 x 10-11

a) Write out both the acidic and basic reactions and label the conjugate pairs in each reaction.

b) Use the Bronsted/Lowry definition of a base to justify one of the labels above.

c) A 20.00 ml sample of 0.100 M H2A solution is titrated with 0.200 M KOH. What will the pH of the solution be after additions of 0, 1.00, 5.00, 10.00, 12.00, 19.80, 20.00, and 23.00 ml of the base?

d) Draw the general shape of the titration curve that would be found for this titration. Label any and all of the following that can be shown on the graph:

equivalence point

end point

maximum buffer point

buffer region

Some labels may be used more than once, some not at all.

2. A roll of unexposed black-and-white film contains about 0.27 g of AgBr before developing. What mass of Na2S2O3 5H2O (hypo) in 1.500 L of solution is required to dissolve the AgBr as Ag(S2O3)2-3?

Kf = 4.7x1013 Ksp = 3.3x10-13

3. A solution is initially [Cl-] = 7.1x10-3M and [CrO4-2] = 1.0x10-4M. Silver ions (Ag+) are slowly added (without altering the volume). What percent of the chloride will remain in solution when the chromate compound first appears? What mass of silver chloride will have been formed?

Ksp (AgCl) = 1.8x10-10

Ksp (Ag2CrO4) = 9x10-12

4. What is the molar solubility of ferrous hydroxide in a buffer solution made of equal volumes of ammonia and ammonium chloride? Ksp of Fe(OH)2 = 7.9x10-15, Kb of NH3 = 1.8x10-5

5. Using the Henderson/Hasselbach logic, derive a formula for the pAl in a solution of aluminum ions, fluoride ions and the aluminum hexafluoride complex ion [AlF6]-3.