AP Chemistry Chapter 5, 18 & 22 Free Response Exam 2010

AP Chemistry Chapter 14 and 15 Free Response Exam 2014 Name ______

II. 50% of your grade will come from these last two questions. You may use a calculator with this section. You will have 43 minutes for this section of the test.

1 1 -11 1. HOI (aq)  H (aq)  OI (aq) Ka = 2.0 x 10

Hypoiodous acid , HOI, is a weak acid that dissociates in water as represented by the equation above. a. Calculate the value of [H1+] in an HOI solution that has a pH of 5.95.

b. Write the equilibrium constant expression for the ionization of HOI in water, then calculate the concentration of HOI(aq) in an HOI solution that has [H1+] equal to 1.8 x 10-6 M.

c. A solution of Ba(OH)2 is titrated into a solution of HOI i. Calculate the volume of 0.215M Ba(OH)2(aq) needed to reach the equivalence point when titrated into a 150.0 mL sample of 0.346 M HOI(aq).

ii. Indicate whether the pH at the equivalence point is less than, greater than, or equal to 7. Explain.

d. Calculate the number of moles of NaOI(s) that would have to be added to 145 mL of 0.260M HOI to produce a buffer solution with [H1+] = 5.00 x 10-8 M. Assume that volume change is negligible.

e. Show all work for calculating the pH of 150 mL of a 0.200 M HOI solution after 050.0 mL of a .150 M NaOH solution has been added.

f. Predict whether HOBr would be a stronger acid or a weaker acid than HOI, and justify your prediction. + + -10 2. NH4 + H2O  NH3 + H3O Ka= 5.59 x 10

a. What two substances act as bases in the equation above?

b. Write an equilibrium expression for the hydrolysis reaction of ammonia.

c. Solve for the Kb of ammonia.

d. 100. milliliters of .10 M Ammonium Chloride solution is to be titrated with NaOH. i. How many moles of NaOH would need to be added to the solution to reach the equivalence point.

ii. What is the pH of the solution at the equivalence point?

e. 100. milliliters of .10 M Ammonium Chloride solution is mixed with 80.0 milliliters of a .20 M solution of Ammonia.

i. What is the [H1+] of the solution?

ii. If 0.200 grams of NaOH were added to the solution, what would the new pH of the solution be?