This appendix presents examples of the chemistry panel’s suggested modifications to the questions on the AP Chemistry 1999 examination, Section II, to make the questions more contextual; to probe more carefully the depth of student understanding; to seek to assess higher-order thinking skills; to require the applications of chemical principles in an enlarged or new context; and to enjoin students to link concepts to chemical systems and macroscale phenomena, not merely see chemical principles as isolated facts. In particular cases below, the original question is given, followed by its suggested modification.
NH3(aq) + H2O(l) ↔ (doubled-headed arrow) NH4+(aq) + OH-(aq)
In aqueous solution, ammonia reacts as represented above. In 0.0180 M NH3(aq) at 25 oC, the hydroxide ion concentration [OH-] is 5.60 x 10-4M. In answering the following, assume that temperature is constant at 25 oC and that volumes are additive.
Write the equilibrium-constant expression for the reaction represented above.
Determine the pH of 0.0180 M NH3(aq).
Determine the value of the base ionization constant, Kb, for NH3(aq).
Determine the percent ionization of NH3 in 0.0180 M NH3(aq).
In an experiment, a 20.0 mL sample of 0.0180 M NH3(aq) was placed in a flask and titrated to the equivalence point and beyond using 0.0120 M HCl(aq).
Determine the volume of 0.0120 M HCl(aq) that was added to reach the equivalence point.
Determine the pH of the solution in the flask after a total of 15.0 mL of 0.0120 M HCl(aq) was added.
Determine the pH of the solution in the flask after a total of 40.0 mL of 0.0120 M HCl(aq) was added.
(SOURCE: CEEB, 1999b, p. 42)