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Home > AP Courses and Exams > 2007 AP Chemistry Exam Format

2007 AP Chemistry Exam Format

by Eleanor Siebert
Mount St. Mary's College
Los Angeles, California

As described in the new 2007, 2008 AP Chemistry Course Description, the AP Chemistry Exam will have a new format beginning in May 2007. It is important to note that the content covered by the exam will not change. The weighting of the two major parts of the exam will change slightly -- Sections I and II will each contribute 50 percent toward the final grade.

Section I (90 minutes) will not change and will still consist of 75 multiple-choice questions with broad coverage of chemistry topics. However, there will be three primary changes in the format of Section II of the 2007 exam. While these changes do not introduce new content, students should be made aware of these changes before taking the exam in May 2007.

The first change in Section II is that students will no longer be asked to choose between alternative questions. All students will do the same six questions: three problems, the first of which is an equilibrium problem; question 4 (reactions); and two essay questions.

A second change in Section II relates to question 4, which assesses students' knowledge about chemical reactions. Currently students are asked to write chemical equations for five of eight given sets of reactants. In the new question 4 format, all students will write balanced chemical equations for three different sets of reactants and will answer a short question about each of the three reactions.

The third change in Section II relates to the timing of Part A (during which calculators are permitted) and Part B (when no calculators are permitted). In Part A, students will have 55 minutes to answer three problems; in Part B, students will have 40 minutes to answer question 4 and questions 5 and 6, the two essay questions.

The table below summarizes the difference between the 2006 and 2007 AP Chemistry Exam Section II formats. Note that the laboratory question can now appear in Part A.

Table 1: A Comparison of the 2006 and 2007 AP Chemistry Exam
Section II Formats

2006 Section II Format 2007 Section II Format
Part A, 40 minutes
(With calculator)
% of Section Score Part A, 55 minutes
(With calculator)
% of Section Score
  • Equilibrium problem
20%
  • Equilibrium problem
20%
  • Other problem (choice)
20%
  • Other problem*
20%
   
  • Other problem*
20%
Part B, 50 minutes
(No calculator)
% of Section Score Part B, 40 minutes
(No calculator)
% of Section Score
  • Reactions question
    (5 of 8 required)
15%
  • Reactions question (3 required)
10%
  • Laboratory essay
15%
  • Essay question*
15%
  • Required essay
15%
  • Essay question*
15%
  • Other essay (choice)
15% *One of the other problems or essays will be based on laboratory

One area of interest among AP teachers lies in the reformatting of question 4; therefore, the remainder of this article will present the reactions that appeared in the 2006 exam and show how these reactions might be recast in the new 2007 format.

The current directions for question 4 are as follows.

4. Write the formulas to show the reactants and the products for any FIVE of the laboratory situations described below. No more than five choices will be graded. In all cases, a reaction occurs. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. You need not balance the equations.
Example: A strip of magnesium is added to a solution of silver nitrate.
Ex. Mg + Ag+ → Mg2+ + Ag


These instructions will be slightly modified in the 2007 exam booklet; the new wording (added in boldface) will be very close to this:

4. For each of the following three reactions, in part (i) write a BALANCED equation and in part (ii) answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction.

Example: A strip of magnesium is added to a solution of silver nitrate.
(i) Mg + 2 Ag+ → Mg2+ + 2 Ag

(ii) Which substance is oxidized in the reaction?
Answer: Magnesium (Mg) metal
As shown, the new directions for question 4 require the students to provide a balanced chemical equation showing only the reacting substances and ask the student to answer a question about the reaction. The majority of the credit for a response will be earned for writing the balanced equation; the remaining credit will be earned for correctly answering the question that follows each reaction, which will require the student to focus more on the meaning of the reaction. For instance, the example given above is an oxidation-reduction reaction. Ask yourself what your students should know about a redox reaction. Here are some questions that I hope most students would be able to answer:
  • Which substance is being oxidized?
  • Which substance is being reduced?
  • What is the change in the oxidation number of the magnesium?
  • What would you observe happening to the magnesium metal strip in this reaction?
Any one of these questions -- and you may be able to come up with more -- is representative of what question 4 will include on the 2007 AP Chemistry Exam. Table 2 (below) lists some sample questions -- suggested by members of the AP Chemistry Development Committee -- that might be asked about the reactions that appeared on the 2006 exam. Part (i) asks for the balanced chemical equation, omitting any ions or molecules that are unchanged in the reaction; part (ii) asks one question that focuses on such things as the type of reaction (redox, proton-transfer, Lewis acid-base, and so forth), the stoichiometry of the reaction, and the physical observations that one might expect as the reaction occurs.

Table 2: Question 4 Reactions on the 2006 AP Chemistry Exam Recast in
the 2007 Format

(a) Solid potassium chlorate is strongly heated and decomposes, resulting in a change in the oxidation numbers of both chlorine and oxygen.

(i) 2 KClO3 → 2 KCl + 3 O2

(ii) What is the oxidation number of chlorine before and after the reaction?

Answer: Chlorine has an oxidation number of +5 in KClO3 and -1 in KCl.

(b) Solid silver chloride is added to a solution of concentrated hydrochloric acid, forming a complex ion.

(i) AgCl + Cl → [AgCl2]

(ii) Which species acts as a Lewis base in the reaction? Explain.

Answer: The chloride ion acts as a Lewis base in the reaction because it donates an electron pair.

(c) A solution of ethanoic (acetic) acid is added to a solution of barium hydroxide.

(i) HC2H3O2 + OH → H2O + C2H3O2

(ii) Explain why a mixture of equal volumes of equimolar solutions of ethanoic acid and barium hydroxide is basic.

Answer: In the mixture there are initially twice as many moles of hydroxide ions as molecules of acid; since they react in a 1:1 ratio, there is an excess of hydroxide ions after the reaction is complete, leading to the basic solution.

(d) Ammonia gas is bubbled into a solution of hydrofluoric acid.

(i) NH3 + HF → NH4+ + F

(ii) Identify a conjugate acid-base pair in the reaction.

Answer: NH3 (base) and NH4+ (acid)
Or: HF (acid) and F (base)

(e) Zinc metal is placed in a solution of copper(II) sulfate.

(i) Zn + Cu2+ → Zn2+ + Cu

(ii) Describe the change in color of the solution that occurs as the reaction proceeds.

Answer: The blue color of the solution due to the presence of the hydrated copper(II) ion fades as the copper(II) ion reacts and the colorless hydrated zinc(II) ion forms.

(f) Hydrogen phosphide (phosphine) gas is added to boron trichloride gas.

(i) PH3 + BCl3 → H3PBCl3

(ii) Which species acts as a Lewis acid in the reaction? Explain.

Answer: BCl3 acts as a Lewis acid in the reaction because it accepts the non-bonded pair of electrons of the phosphorus atom in PH3.

(g) A solution of nickel(II) bromide is added to a solution of potassium hydroxide.

(i) Ni2+ + 2 OH → Ni(OH)2

(ii) Identify the spectator ions in the reaction mixture.

Answer: The spectator ions are the bromide ion (Br) and the potassium ion (K+).

(h) Hexane is combusted in air.

(i) 2 C6H14 + 19 O2 → 12 CO2 + 14 H2O

(ii) When one molecule of hexane is completely combusted, how many molecules of products are formed?

Answer: 1 molecule of hexane produces 13 molecules of products.



The examples given in the table represent one kind of question about each reaction; there are many more such questions that can be asked, but recall that these questions should not require the use of a calculator, which is not permitted for Part B of Section II of the exam. If you ask your students to write and answer a question about each reaction that they study, then they will be very well prepared to tackle question 4 on the 2007 AP Chemistry Exam!

Eleanor D. Siebert is the Chief Reader for AP Chemistry.



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