The Advanced Placement (AP) Program bridges high schools and colleges by allowing high school students to do college-level work for college credit. The AP Chemistry Exam is one of more than 30 college-level examinations offered every year.
AP courses are offered by more than 10,000 high schools in the United States, Canada, and more than 60 additional countries. More than 3,000 colleges around the world offer college credit to students who perform well on AP tests. The specific score required for credit varies from school to school and from subject to subject.
The AP Program is coordinated by the College Board. The College Board is a national nonprofit organization composed of representatives from various schools and colleges. They see it as their mission to set educational standards.
The College Board appoints a development committee for each of the subjects. The development committee decides what should be covered in an AP course and how it should be covered on the AP test. The AP Chemistry development committee is composed of three high school chemistry teachers, three college professors who teach general chemistry, and an additional college professor who chairs the group. Each member of the development committee serves a three-year term.
The test is administered by the Educational Testing Service (ETS)—the same folks who bring you the SAT. ETS also plays a role in developing the test.
The AP Chemistry Exam is a three-hour-long, two-section test that attempts to cover the material you would learn in a college first-year chemistry course. The first part, which counts for 50 percent of your grade, consists of multiple-choice questions. The second part, which counts for 50 percent of your grade, is composed of free-response questions, such as short essays and problems involving calculations.
The test is offered once every year in May. It’s scored in June. The multiple-choice section is scored by computer and the problems and essays are scored by a committee of high school and college teachers. The problems and essays are graded according to a standard set at the beginning of the grading period by the chief faculty consultants. Inevitably, the grading of Section II is never as consistent or accurate as the grading of Section I.
When the grading is done, the results are curved and each student receives a grade based on a five-point scale. For the AP Chemistry Exam, the results break down as follows:
Although standards vary from school to school, it’s safe to say that most colleges will give credit for a 5, some will give credit for a 4 or 3, and very few will give credit for a 2.
Section I of the test is composed of 75 multiple-choice questions, for which you are allotted 90 minutes. This part is worth 50 percent of your total score.
For this section, you will be given a periodic table of the elements and you may NOT use a calculator. The College Board says that this is because the new scientific calculators not only program and graph but also store information—and they are afraid you’ll use this function to cheat!
The first 15 multiple-choice questions, give or take a few, will be formatted with 5 answer choices followed by a series of questions (as shown on the next page).
1. This species contains ionic bonds. (E)
2. This species is a gas at standard temperature and pressure. (A)
3. This species is denser as a liquid than as a solid. (B)
4. This species contains a double bond. (A)
These are mostly straightforward, “you know it or you don’t” questions. Notice that an answer can be used once, more than once, or not at all.
The rest of the multiple-choice questions are in the standard question-and-answers format shown below.
16. Which of the following species is a gas at standard temperature and pressure?
(A) O2
(B) H2O
(C) Ni
(D) Fe
(E) NaCl
On the multiple-choice section, you receive 1 point for a correct answer. There is no penalty for leaving a question blank or getting a question wrong.
Your raw score on this section will be just the number of questions you answered correctly. You can make a rough prediction of your overall score from your raw score on the multiple-choice section, assuming that you do about as well on the free-response section.
Roughly speaking,
So you can get a 5 with a raw score of 50, a 4 with a raw score of 35, and a 3 with a raw score of 25. That’s a pretty generous curve. According to the College Board, the multiple-choice section of the AP Chemistry Exam covers more material than any individual student is expected to know. Nobody is expected to get a perfect or even near-perfect score.
What does that mean to you?
You can skip every third question and still get a 5. You can skip half the questions and still get a 4. You can skip two out of every three questions and still get a 3. Obviously, you should answer any question that you have a chance of getting right, but you should be aware that the grading curve gives you plenty of slack.
Okay, so you know that you can skip questions. How do you know which questions to skip?
Go through the multiple-choice section twice. The first time, do all the questions that you can get answers to immediately. That is, do the questions with little or no math and questions on chemistry topics in which you are well versed. Skip questions on topics that make you uncomfortable. Also, you want to skip the ones that look like number crunchers (even without a calculator, you may still be expected to crunch a few numbers). Circle the questions that you skip in your test booklet so you can find them easily during the second pass. Once you’ve done all the questions that come easily to you, go back and pick out the tough ones that you have the best shot at.
In general, the questions near the end of the section are tougher than the questions near the beginning. You should keep that in mind, but be aware that each person’s experience will be different. If you can do acid-base questions in your sleep, but you’d rather have your teeth drilled than draw a Lewis diagram, you may find questions near the end of the section easier than questions near the beginning.
That’s why the Two-Pass System is so handy. By using it, you make sure you get to see all the questions you can get right, instead of running out of time because you got bogged down on questions you couldn’t do earlier in the test.
This brings us to another important point.
Most people don’t run out of time on standardized tests because they work too slowly. Instead, they run out of time because they spend half the test wrestling with two or three particular questions.
You should never spend more than a minute or two on any question. If a question doesn’t involve calculation, then either you know the answer, you can make an educated guess, or you don’t know the answer. Figure out where you stand on a question, make a decision, and move on.
Any question that requires more than two minutes’ worth of calculations probably isn’t worth doing. Remember, skipping a question early in the section is a good thing if it means that you’ll have time to get two correct answers later on.
You get one point for every correct answer on the multiple-choice section. Guessing randomly neither helps you nor hurts you. Educated guessing, however, will help you.
There is a fundamental weakness to a multiple-choice test. The test makers must show you the right answer, along with four wrong answers. Sometimes seeing the right answer is all you need. Other times you may not know the right answer, but you may be able to identify one or two of the answers that are clearly wrong. Here is where you should use POE to take an educated guess.
Look at this hypothetical question.
1. Which of the following compounds will produce a purple solution when added to water?
(A) Brobogdium rabelide
(B) Diblythium perjuvenide
(C) Sodium chloride
(D) Hynynium gargantuide
(E) Carbon dioxide
You should have no idea what the correct answer is because three of these compounds are made up, but you do know something about the obviously wrong answers. You know that sodium chloride, choice (C), and carbon dioxide, choice (E), do not turn water purple. So, using POE, you have a one-out-of-three chance at guessing the correct answer. Now the odds are in your favor. Now you should guess.
In the example above, we eliminated two wrong answers, but even eliminating one wrong answer puts the odds in your favor. Of course, the more wrong answers you can eliminate, the better.
Remember, you’re guessing. Pondering the possible differences between brobogdium rabelide and diblythium perjuvenide is a waste of time. Once you’ve taken POE as far as it will go, pick your favorite letter and move on.
Remember, the multiple-choice section is the exact opposite of the free-response section. It’s scored by a machine. There’s no partial credit. The computer doesn’t know, or care if you know, why an answer is correct. All the computer cares about is whether you blackened in the correct oval on your score sheet. You get the same number of points for picking (B) because you know (A) and (E) are wrong and B is a nicer letter than C or D as you would for picking (B) because you fully understood the subtleties of an electrochemical process.
You will NOT be allowed to use a calculator on this section. That shouldn’t worry you. All it means is that there won’t be any questions in the section that you’ll need a calculator to solve.
Most of the calculation problems will have fairly user-friendly numbers—that is, numbers with only a couple of significant digits, or things like “11.2 liters of gas at STP” or “160 grams of oxygen” or “a temperature increase from 27°C to 127°C.” Sometimes these user-friendly numbers will actually point you toward the proper steps to take in your calculations.
Don’t be afraid to make rough estimates as you do your calculations. Sometimes knowing that an answer is closer to 50 than to 500 will enable you to pick the correct answer on a multiple-choice test (if the answer choices are far enough apart). Once again, the rule against calculators works in your favor because the College Board will not expect you to do very precise calculations by hand.
There may be a couple of real number-crunching problems on the test. If you can recognize them quickly, these are good ones to skip. There’s no point in spending five minutes crunching numbers to get one problem right if that time could be better used in getting three others correct later in the test.
Section II is composed of a series of six free-response questions, all of which are required. You will be allotted 95 minutes to complete this section, which is worth 50 percent of your total score. You get exactly 55 minutes for Part A, which is composed of three problems requiring calculation, then 40 minutes for Part B, which is composed of two essay questions and one question concerning chemical reactions.
For Part A, you will be given a table of commonly used chemical equations, a table of standard reduction potentials, and a periodic table. You may use a calculator, which you will probably need.
This is a multipart question involving calculation to determine some aspect of equilibrium.
This question will be divided into at least four or five parts, with partial credit available for correct answers on each part. The question is worth 20 percent of Section II. The average score for this question is usually less than half credit.
Part A also includes two additional multipart questions that will involve calculation. These questions can come from any topic in the syllabus and one of them may be based in a laboratory setting. The test makers will probably do their best to include concepts from as many different chemistry topics as possible in the different parts of each problem.
These questions, like the equilibrium question, will be divided into at least four or five parts, with partial credit available for correct answers on each part. Each of these questions is worth 20 percent of Section II. The average score for these questions is usually less than half credit.
On Part A, you want to show the graders that you can do chemistry math, so here are some suggestions.
Show every step of your calculations on paper
This section is the opposite of multiple choice. You don’t just get full credit for writing the correct answer. You get most of your points on this section for showing the process that got you to the answer. The graders give you partial credit when you show them that you know what you’re doing. So even if you can do a calculation in your head, you should set it up and show it on the page.
By showing every step, or explaining what you’re doing in words, you insure that you’ll get all the partial credit possible, even if you screw up a calculation.
Include units in all your calculations
Scientists like units in calculations. Units make scientists feel secure. You’ll get points for including them and you may lose points for leaving them out.
You can lose one point per question if your answer is off by more than one significant figure. Without getting too bent out of shape about it, try to remember that a calculation is only as accurate as the least accurate number in it.
The graders will follow your reasoning, even if you’ve made a mistake
Often, you are asked to use the result of a previous part of a problem in a later part. If you got the wrong answer in part (a) and used it in part (c), you can still get full credit for part (c), as long as your work is correct based on the number that you used. That’s important, because it means that botching the first part of a question doesn’t necessarily sink the whole question.
Remember the mean!
So let’s say that you could only complete parts (a) and (b) on the required equilibrium problem. That’s 4 or 5 points out of 10, tops. Are you doomed? Of course not. You’re above average. If this test is hard on you, it’s probably just as hard on everybody else. Remember, you don’t need anywhere near a perfect score to get a 5, and you can leave half the test blank and still get a 4!
You will not be allowed to use a calculator for Part B, which requires you to write balanced equations for chemical reactions and answer questions about chemical concepts.
For this section, you will be given a table of standard reduction potentials and a periodic table and you may not use a calculator.
You will be given 3 sets of chemical reactants and you will be asked to write the appropriate balanced equation for the reaction that will occur for each. Each reaction will be followed by a brief question that will focus on some aspect of the reaction.
Each reaction is worth 5 points; 1 point for reactants, 2 points for products, 1 point for balancing, and 1 point for the question; so you can earn a total of 15 points for this section. This part is worth 10 percent of Section II.
We’ll talk about how to approach this section in Chapter 17.
For the two essay questions, you will be given a table of commonly used chemical equations, a table of standard reduction potentials, and a periodic table. You may not use a calculator for this section, which is fine because there won’t be any calculations.
The essays are multipart conceptual questions, with stress on understanding and explaining chemical concepts, rather than on doing calculations. These questions can come from any topic in the syllabus and one of them may be based in a laboratory setting. As in the problems, the test makers will probably try to include questions from as many different chemistry topics as possible. Partial credit will be given for correct answers on each part, and each question is worth 15 percent of Section II.
This section is here to test whether you can translate chemistry into English. The term “essay” is a little misleading because all of these questions can be answered in two or three simple sentences, or with a simple diagram or two. Here are some tips for answering the two essay questions on Part II.
Show that you understand the terms used in the question.
If they ask you why sodium and potassium have differing first ionization energies, the first thing you should do is tell them what ionization energy is. That’s probably worth the first point of partial credit. Then you should tell them how the differing structures of the atoms make for differing ionization energies. That leads to the next tip.
Take a step-by-step approach.
Grading these tests is hard work. Breaking a question into parts in this way makes it easier on the grader, who must match your response to a set of guidelines he or she has been given that describe how to assign partial and full credit.
Each grader scores each test based on these rough guidelines that are established at the beginning of the grading period. For instance, if a grader has 3 points for the question about ionization energies, the points might be distributed the following way:
One point for understanding ionization energy.
One point for explaining the structural difference between sodium and potassium.
One point for showing how this difference affects the ionization energy.
You can get all three points for this question if the grader thinks that all three concepts are addressed implicitly in your answer, but by taking a step by step approach, you improve your chances of explicitly addressing the things that a grader has been instructed to look for. Once again, grading these tests is hard work; graders won’t know for sure if you understand something unless you tell them.
This leads us to an obvious point.
Write neatly.
Even if writing neatly means working at half-speed. You can’t get points for answers if the graders can’t understand them. Of course, this applies to the rest of the free-response section as well.
The graders will follow your reasoning, even if you’ve made a mistake
Just like in the problems section, you might be asked to use the result of a previous part of a problem in a later part. If you decide (incorrectly) that an endothermic reaction in part (a) is exothermic, you can still get full credit in part (c) for your wrong answer about the reaction’s spontaneity, as long as your answer in (c) is correct based on an exothermic reaction.
These are the topics covered on the AP Chemistry Exam, as described by the College Board.
(1) Constants for acids and bases, pK, pH
(2) Solubility product constants and their application to precipitation and the dissolution of slightly soluble compounds
(3) Common ion effect, buffers, hydrolysis
Questions based on experiences and skills students acquire in the laboratory: making observations of chemical reactions and substances, recording data, calculating and interpreting results based on the quantitative data obtained, lab safety, experimental errors
The following list summarizes types of specific chemical calculation problems that may appear on the test: