Section II (Free-Response Questions)
Part A: Question 1
Directions:Clearly show the methods used and steps involved in arriving at your answers. It is
to your advantage to do this, because you may earn partial credit if you do, and you will re-
ceive little or no credit if you do not. Attention should be paid to significant figures. Be sure to
write all your answers to the questions on the lined pages following each question the booklet.
The Section II score weighting for this question is 20%.
Solve the following problem.
- Ethylamine reacts with water as follows:
C 2 H 5 NH 2 (aq) + H 2 O(l)→C 2 H 5 NH 3 +(aq) + OH–(aq)
The base-dissociation constant, Kb, for the ethylamine ion is 5.6 × 10 –4.
(a) A student carefully measures out 65.987 mL of a 0.250 M solution of ethylamine.
Calculate the OH–ion concentration.
(b) Calculate the pOH of the solution.
(c) Calculate the % ionization of the ethylamine in the solution in part (a).
(d) What would be the pH of a solution made by adding 15.000 grams of ethylammonium
bromide (C 2 H 5 NH 3 Br) to 250.00 ml of a 0.100-molar solution of ethylamine?
(e) If a student adds 0.125 grams of solid silver nitrate to the solution in part (a), will silver
hydroxide form as a precipitate? The value of Kspfor silver hydroxide is 1.52 × 10 –8.Part A: Question 2 or 3
Directions:Answer either Question 2 or 3. Only one of these two questions will be graded. If
you start both questions, be sure to cross out the question you do not want graded. The Section
II score weighting for the question you choose is 20%.
- Water is introduced into a test tube that contains 2.51 grams of SbCl 3. The products of the
reaction are collected, analyzed, and found to be
- 1.906 gram of a solid containing only antimony, oxygen, and chlorine.
- 0.802 grams of a single gas that is found to be 97.20% by weight chlorine and 2.75% by
weight hydrogen.
(a) Determine the simplest formula for the gas.
(b) What fraction of the chlorine atoms are found in the solid compound, and what frac-
tion are found in the gas phase, after the reaction?
Part IV: AP Chemistry Practice Test