Common Questions About the AP Chemistry Exam

Each year around this time, the same questions start emerging on listservs and discussion boards about the structure and content of the AP Chemistry Exam. Teachers start to worry if they have covered all of the content and if their students are prepared enough for the daunting exam.

The AP Exam Course and Exam Description (CED) is a valuable tool to answer all questions, but it is dense and sometimes hard to navigate. The best advice I have for new AP teachers at this time of the year is to take all of the released exams as if you were a student. Familiarize yourself with how the exam is organized, how it looks when it is printed, how many questions there are, what topics come up the most, etc. It sounds like a lot, but when I first started teaching AP Chemistry I took every exam available. There are now practice exams available if you log into the College Board AP Course Audit Site. These practice exams are gold because they are formatted to match the actual exam. The practice exams contain answer sheets, guides for grading the exam, as well as scaling for the exam, and each question cites the learning objective that is elicited in the question. The practice exams should be secure, in that students should only use them in class. (Secure practice exams were created so teachers can use them to assess their students. The questions and answers should never be readily available online for students to see.) Even with all of the available resources, there are still many unanswered or unclear questions about the AP Chemistry Exam. I have compiled a few and will do my best to answer each question.

 

QUESTIONS ABOUT THE EXAM FORMAT AND GRADING

How is the exam formatted?

It is a great idea to familiarize your students with the format of the exam in order to allow for proper expectations and to plan their time most effectively. Most of this information can be found on the second page of this link.

• The AP Chemistry Exam Section I consists of 60 multiple choice questions, 10 of which are field testing questions (these questions will not be counted towards their final grade, but the students will have no way of knowing which questions the field testing questions are).
• The questions are bound in a book with a reference table in which they have to turn back and forth between the questions and the tables.
• Students may write notes and scratch work anywhere on the exam, but are required to answer the questions on the provided answer sheet within 90 minutes. Exam readers that attend the reading in June never see these multiple-choice questions.
• Students cannot use any calculators during the multiple choice section of the exam.
• Students should be given a short break between the multiple-choice section and the free response section. The students receive all new exam packets for section II. The students are given a new bound book containing a fresh reference table.
• The free response section consists of three long questions, each requiring an average of 23 minutes and awarding the students up to ten points each.
• There are also four short questions requiring an average of nine minutes and awarding up to four points each.
• Each free response question is written on one to two pages with no space for work. After the question, multiple pages of paper are provided in the bound book for the responses.
• Students are encouraged to use a calculator during the free response section of the exam.
• Section I multiple choice questions account for 50% of the exam score; section II free response accounts for the other 50% of the total score.

 

Why are the secure practice exams only 50 multiple choice questions, while the actual AP Chemistry Exam has 60 multiple choice questions?

As stated above, ten of the 60 multiple choice questions on the AP Chemistry Exam are field test questions and will not count toward the students’ grade. There is no way to know which questions they are while taking the exam, so the students need to answer every question. The College Board has chosen to omit those field questions and only release the 50 gradable questions. Now an additional question arises; what do I do about the timing and grading for my "in class" practice exam? Well, you have a few options:

1. Leave the practice exam as is and only allow 75 minutes to answer the 50 questions. Each multiple choice question should take approximately 1.5 minutes on average to answer regardless of the sum of the questions. Then, use the grading rubric found at the end of the practice exam to score the exam.
2. Add ten more questions of your own and keep the 90-minute time limit. Then you must decide: would you like to grade those extra ten questions and change the grading scale? Or should you not grade those questions and keep the grading scale intact?

 

Can students write in pen or pencil on the AP Exam?

Either pen or pencil are ok. Pencils are great to fix mistakes, however, tell students to write legibly and dark. Light pencil is difficult to read.

 

If a student makes a mathematical error in the first part of a question, are they punished on the next part (double jeopardy)?

There is no double jeopardy. If a student makes an error in part a and needs to use it in part b, the AP reader will follow along with the math to ensure they have the new correct answer. It is more important that the student shows an understanding of how to solve part b than for the student to have carried down the correct numbers.

 

QUESTIONS ABOUT THE EXAM CONTENT

In this section, I will try to answer questions that have come up time and time again about the content of the exam. Where applicable, I have cited an exam question that deals with the topic. You can find these exams on the College Board AP Chemistry Exam website when you scroll down the page.

 

How are significant figures scored on the AP Exam?

One answer will be scored on the entire short answer section per exam. This is one point out of the 100 total points of the exam. The exam question associated with significant figures will most likely not be labeled and the students will have no way of knowing when to use significant figures; therefore, they must round their answers to the appropriate number of significant figures for every calculation to obtain the single point. Since significant figures carry so little weight on the AP Exam, teachers may not need to emphasize them as much as we probably do in class. Here’s a significant figures tip though: try to make sure students don’t round molar masses to values less than the number of significant figures given in the example. Don’t round the molar masses from the periodic table that is provided with the AP Exam. Another way significant figures can be addressed is when reading measurements. Be sure to teach students to read “a place beyond” what they see on the device. For example, the 2018 Exam question 1d asked students to report a temperature change from the graph and students needed to report 12.5 degrees Celsius, whereas 12 and 13 were not accepted. (Also reference 2016 Exam question 7a.)

 

Do the solubility rules need to be memorized?

Since the redesign in 2014, students should know that group 1 ions, acetate, nitrate, and ammonium ions are soluble. All other rules will be considered insoluble unless noted in the stem of a question.

 

Does the activity series need to be memorized?

No. But, knowing that there is one can be relevant. Students should be able to explain reactivity with a group of metals or nonmetals. Some teachers still hand out the standard reduction tables from the old AP Exam reference tables and use them to tie in to electrochemistry in order to predict which species is more likely to be reduced or oxidized (2017 Exam question 7a and 2016 Exam question 3e).

 

Net ionic equations used to take up all of question 4 on the exam. Are they no longer assessed?

They are absolutely assessed. Instead of having an entire question devoted to reaction writing, net ionic equations have been factored into the other questions. On the 2018 exam, question 1g asked for the balanced net ionic equation for a given reaction. In 2017, question 3ci, students could have used a net ionic equation to help them explain their answer. In 2016, question 3f, students created a net ionic equation from half reactions. In addition, many net ionic equations will appear in the multiple choice section of the exam.

 

Will students need to memorize electronegativity values in order to determine types of bonds?

No. Instead have students learn the general trends for periods and groups. Start the unit by practicing these trends using a table of electronegativity values and then we move on to just using the trends to determine polarity. I do have my students memorize that carbon and hydrogen are close enough to be considered nonpolar.

 

While teaching intermolecular forces of attraction, how will students know when London dispersion forces are stronger than hydrogen bonding?

A data table will be given with boiling points or other evidence of compounds that need to be compared. Generally, London dispersion forces are the weakest force present in all compounds, but dependent on the number of polarizable electrons, these forces can multiply quickly (2018 Exam question 4a and 2017 Exam question 1dii). A common mistake some students make is they try to reason against the exam data and argue the data is incorrect. It is important to explain to students that unless the question is asked, “Do you agree or disagree…” then the data given is unarguable.

 

Students really need to memorize all of the VSEPR shapes, bond angles, and hybridizations!?

Yes. There is no way around it. All geometries, including those of expanded octets should be known, as well as their general bond angles. Understanding that increasing the number lone pairs on a central atom will decrease the bond angle is helpful, but the actual values aren’t assessed (2017 Exam question 1cii). Hybridization is limited to compounds that obey the octet rule, and therefore limited to sp, sp², and sp³ (2015 Exam question 1e).

 

Do students always need to draw the structure that reduces the formal charge?

No. Structures that obey the octet (and may not have a reduced formal charge) are acceptable. Formal charges can be used to rationalize which structure may be a better representation of the bonding in a specific molecule (2017 Exam question 2a).

 

Will students need to calculate the lattice energy of an ionic compound?

No. They should know how to qualitatively compare lattice energy values of various compounds using Coulomb’s Law by comparing atomic radii and the distance between the ions (2018 Exam question 3c and 2017 Exam question 6b).

 

Do students need to me memorize all of the polyatomic ions?

Students can perform decently well on the AP chemistry Exam without fully memorizing the polyatomic ions. However, knowing the polyatomic ions will help with strong acids and bases, formula writing, electrochemistry, etc. I have my students memorize the important”-ates” (such as sulfate, acetate, nitrate, phosphate, carbonate) and then understand the rules for “-ites,” “hypo—ites,” and “per—ates.” A lot of teachers also use a mnemonic device known as “Nick the Camel”. I looked it up on Google and started using it this year. My students loved it.

 

Does the order of electron configuration matter? And should they know the exceptions for d⁴ and d⁹ groups?

Students are allowed to write 3d before or after 4s as long as they have an understanding that the 4s sublevel is the valence sublevel in which electrons will be removed and added to first. Exceptions to the Aufbau are no longer assessed.

 

Are phase diagrams (triple point diagrams) assessed? Crystal structures? Lewis acids and bases? Colligative properties?

No. I still use phase diagrams to practice graphical analysis and discuss relationships between temperature and pressure. Crystal structures are no longer assessed. Lewis acids and bases are not assessed. Colligative properties are not calculated, as they are considered part of a first year chemistry course (AP chemistry is a second year course according to College Board).

 

Do students need to graph integrated rate laws?

No. Students do not need to have a graphing calculator at all. When the integrated rate laws are referenced in questions it is usually easily answered with the concept that zero order reactions are graphed [A] versus time, first order reactions are graphed ln[A] versus time, and second order reactions are graphed 1/[A] versus time. Whichever graph is the straighter line is the correct order of the species (2016 Exam question 5b). In the 2107 exam question 2eii, the students were given an exponential decay graph of a species and asked to explain how the graph represents a first order proposed rate law. Some students tried to graph the data by running the natural log of the given concentrations versus time, but the students only obtained credit if they proved they actually graphed the data by showing the calculations and retention values. Most students did not provide the proof needed to answer the question and merely stated, “If I had graphed the natural log of the concentration versus time I would have obtained a straight line that would indicate first order” which was not enough. The acceptable answer was that the graph represents a decomposition reaction with a constant half-life, which proves it is first order. As you can see, these questions do not need the graph to be created and can be answered by other means. Having stated this, I still have my students perform labs with graphing calculators for the experience of knowing what to set at x and y axes.

 

Do students need to use the quadratic formula for acid base equilibrium questions?

No. Many calculations can be solved one of three ways. Either an equilibrium concentration is given in the stem of the question which can be used to determine the “x” value (2017 Exam question 3b or 2014 Exam question 2b), the equilibrium expression has squares on both the numerator and denominator in which one can take the square root (for example x²/(5-x)² found in question in multiple choice sections), or the value of the equilibrium constant is so small the student can say the change in concentration of the given species is negligible; therefore, eliminating the change in the equilibrium expression, taking the square root of both sides and solving without a quadratic equation (2016 question 4a). In the last scenario, which is very common, students do not need to prove the change is small enough to be ignored, however, if asked what the final concentration is of the initial species, or if asked to plug it into another formula such as percent ionization of the acid, students do need to subtract the x value (change value) from the initial concentration value, in case it does show a slight decline in concentration at equilibrium (2018 question 5b).

 

Will students need to balance redox reactions in acidic and basic solutions?

Not entirely. Students may be given two half reactions that they may need to cancel species and sum for an overall reaction that have already been balanced in acidic or basic conditions. Or, students may need to pick out one half reaction from an overall reaction (2018 Exam question 3d). I still have my students learn the method of balancing so they know where those half equations that were given originated and are not seeing it for the first time on the exam. Generally, students still need to be able to assign oxidation numbers, determine which species is oxidized and which is reduced, and sum reactions. The reducing agent and oxidizing agent terms and concepts has been removed from the AP Exam. Therefore, practicing this method of balancing in acidic or basic solutions helps practice other learning objectives but is not directly assessed.

 

What do students need to know about organic compounds?

There are no direct organic chemistry questions on the AP Chemistry Exam. Students will not be asked to name organic compounds, identify isomers, or organic reactions. Some questions may use organic compounds in questions about Lewis Structures and bond angles, or for intermolecular forces of attraction comparisons. Therefore, it is a good idea to use organic compounds in class during these topics. But there is no need to focus on nomenclature or specifics about organic chemistry. All questions involving organic compounds can be answered using bonding, intermolecular forces, or other topics in the curriculum.

 

Is the [Kc/Kp conversions, Arrhenius equation, Nernst equation, Freezing point depression calculation, Molecular Orbital Theory, root mean square velocity, etc.] on the exam?

Generally, if it isn’t on the AP Chemistry reference table, it is not something the students will need to calculate. Make sure you have the most up to date equations list, as items have been removed since the exam redesign. It is your decision if you would like to teach past the scope of the course, knowing that some of these equations might help describe and prove chemical phenomenon better. Some items I did have my students memorize as far as calculations are concerned are:

• Enthalpy Change = [Sum of the Bonds Broken] – [Sum of the Bonds Formed] (2017 question 2b)
• M₁V₁=M₂V₂ for dilutions (although two molarity calculations can be used)

 

I have two weeks left and three topics to teach, what can I leave out?

This is quite a tricky question. Everything in chemistry in interconnected. It is hard to fully understand the scope of chemistry without every piece of the puzzle. It is equally difficult to pack in this much information into one year. I coded the last six practice exams (multiple choice and short answer) by subtopic to use as reference when I write my own exams. I found that the most assessed topics include: stoichiometry, bonds and intermolecular forces, kinetics, equilibrium, acids and bases, and thermodynamics. The less assessed topics appear to be atomic structure, periodicity, and electrochemistry. Again, all topics should be covered and will be assessed on each exam. But skipping a topic such as acid base chemistry would be a major mistake.