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The Best AP Chemistry Review Guide 2020

Posted by Samantha Lindsay | Mar 21, 2020 10:08:00 AM

Advanced Placement (AP)

 

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Not sure how to begin studying for the AP Chemistry exam? This review guide will help you figure out what's on the test and how you can ace it.

I'll go over the AP Chem exam structure, provide sample questions in each format, list the concepts you can expect to see on the test, and give you some tips on how to get the most out of your studying. I just looked into my PrepScholar Crystal Ball™ and saw a 5 in your future, so get ready to kick this test's butt.

 

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2020 AP Test Changes Due to COVID-19

Due to the COVID-19 coronavirus pandemic, AP tests will now be held remotely, and information about how that will work is still evolving. Stay up to date with the latest information on test dates, AP online review, and what this means for you with our AP COVID-19 FAQ article.

 

What's the Format of the AP Chemistry Exam?

The AP Chemistry exam is 3 hours and 15 minutes long and has two sections: multiple-choice (90 minutes long) and free-response (105 minutes long). There are 60 multiple-choice questions and seven free-response questions. The free-response section contains three long response (worth 10 points each) and four short response (worth four points each) questions. You're allowed to use a calculator on the free response section, but you can't use one for multiple-choice.

Time management is important on the AP Chemistry exam because you can easily get caught up in difficult problems. Try not to spend more than a minute on each multiple-choice question during your first pass through the section so that you don't miss any questions at the end that you could have answered. You'll have time to go back and revisit the ones you skipped if you pace yourself. For the free-response questions, you should limit your time to around 5-10 minutes for short response questions and 15-20 minutes for long response questions.

 

What Do AP Chemistry Questions Look Like?

The following are examples of official AP Chemistry questions in multiple-choice, short response, and long response format. I'll go over the answers in detail to give you a sense of the types of problems you'll face on the test and how you might solve them.

 

Multiple-Choice Sample Question

Multiple-choice AP Chemistry questions are often chunked together. In other words, several questions will pertain to a single experiment or dataset. Here's an example:

 

pcl.png

 

In this case, you're asked why a certain outcome resulted from an experiment. You need to know why the pressure in the container would increase based on the changes that occurred. A and B suggest that the increase in pressure has to do with intermolecular attractions either decreasing or increasing in the flask. These choices are incorrect because the intermolecular attractions between these molecules wouldn't be significant enough to make a difference in the pressure of the container.

For Choice C, the first part is correct: the number of molecules has increased with the decomposition of PCl5.It also makes sense that this would result in a higher frequency of collisions with the walls of the container. This answer is looking pretty good.

Choice D is wrong because there's no reason to expect that the molecules have increased in speed inside the container during the reaction.

Since we ruled out all the other options, Choice C is the correct answer!

 

Short Response Sample Question

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For part A, you needed to draw out the interactions between the ions and water molecules in the solution. Three points were awarded for:

  • A representation of at least one Li+ ion and one Cl- ion clearly separated and labeled correctly
  • Each ion surrounded by at least two water molecules
  • Water molecules must be oriented correctly (oxygen end is closer to the lithium ion, and hydrogen end is closer to the chloride ion)

 

Part b was worth one point for identifying the chemical species and providing justification. The species produced at the cathode would be H2(g) and OH-(aq) (you could say either one of these for the point). The hydrogen atoms in water are reduced to H2 at the cathode because this reaction has a lower magnitude reduction potential than that of the reduction of lithium ions to Li (-0.83 vs. -3.05).

 

Long Response Sample Question

Here's an example of a long free-response question from the 2015 exam:

 

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This question expects a lot from you. There's stoichiometry, chemical bonds, intermolecular forces, Lewis diagrams, and thermodynamics! It's testing whether you can apply a bunch of disparate skills that you've learned throughout the year to the scenario presented on the test.

 

Let's look at part a:

For part i of part a, we need to calculate the number of moles of ethene that are produced in the experiment and measured in the gas collection tube. The first step is to calculate the pressure of the ethene so that we can use the ideal gas law to figure out the number of moles of gas produced. We can find the pressure of the water by using the given figure for water's vapor pressure at 305 K: 35.7 torr. Since 1 atm = 760 torr, we can convert the vapor pressure to atm like so:

35.7 torr x (1 atm/760 torr) = 0.047 atm

Then, we can find the vapor pressure of the ethene by subtracting that number from the total vapor pressure of the gas produced:

0.822 atm (total vapor pressure) - 0.047 atm (water's vapor pressure) = 0.775 atm (ethene's vapor pressure)

Finally, we can use the ideal gas law to figure out how many moles of ethene were produced:

PV = nRT
n = PV/RT
n = (0.775 atm)(0.0854 L)/(0.08206 L atm mol-1 K-1)(305 K)
n = 0.00264 moles of ethene produced

 

OK, now let's move onto part ii of part a.

How many moles of ethene would be produced if the dehydration reaction went to completion? To solve this problem, we need to reference the total amount of ethanol originally put into the tube, 0.2 grams, as well as the molar mass of ethanol. Using these numbers, we can see how many moles of ethanol were put into the tube:

0.2 grams ethanol x (1 mole ethanol / 46.1 grams) = 0.00434 moles of ethanol

Ok, that's the number of moles of ethanol that were put in, but we're trying to find the number of moles of ethene that would result if the reaction went to completion. Since both molecules have coefficients of 1 in the equation, they exist in a one to one mole ratio. This means that the answer is 0.00434 moles of ethene.

 

Now for part b!

The percent yield of ethene in the experiment is pretty easy to find based on our answers to part a. We know that the amount of ethene that was actually produced was 0.00264 moles. The amount that would have been produced if the reaction went to completion was 0.00434 moles. To find the percent yield, we can just divide 0.00264 by 0.00434 and multiply the answer by 100:

0.00264 mol / 0.00434 mol x 100 = 60.8 percent yield

 

In part c, you are asked to agree or disagree with the student's claim that the reaction at 298 K has an equilibrium constant of less than 1 and provide justification in the form of calculations for△G°298. According to the formula sheet:

△G° = △H° - T△S°
△G° = 45.5 kJ/mol - (298 K)(0.126 kJ/ K*mol)
△G° = 8.0 kJ/mol

Referencing our formulas again, the equilibrium constant, Kp, is equal to e(-△G°/RT). Since we found that △G° was greater than 0, Kp has to be e raised to some negative number, resulting in a solution equal to a number less than 1. The student is correct that Kp must be less than 1 at 298 K.

 

Part d asks you to complete a Lewis electron-dot diagram. Your answer would look like this:

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The diagram should include all the bonding pairs, plus two non-bonding pairs on the O atom.

 

In part e, you're asked to determine the C-O-H bond angle. This molecule is tetrahedral around the oxygen atom. That means that the bond angle is approximately 109.5 degrees. On this question, you got a point for any answer between 100 and 115 degrees. Technically, the bond angle would be a little smaller because of the two unbonded electron pairs on the oxygen atom. For visual reference:

ethanol.jpg

 

In part f, you have to explain why ethene was collected as a gas after the experiment and ethanol was not. This happened because ethene isn't as soluble as ethanol in water. Ethene is only slightly water-soluble because the weak dipole intermolecular attractions between nonpolar ethene molecules and polar water molecules are weaker than the hydrogen bonds between water molecules. Ethanol molecules are water soluble because they're polar, so they form hydrogen bonds with water molecules as they dissolve.

 

body_polarbears.jpgThese bears are like ethanol and ethene. The one on the left is ethanol because it's CLEARLY more polar.

 

Again, notice how many different skills we used in this one question. We had to know how to:

  • Calculate the number of moles of a gas that were produced by a reaction given the temperature, vapor pressure and volume (with vapor pressure calculated indirectly)
  • Calculate the number of moles of a gas produced by a reaction taken to completion given the mass of the reactant
  • Calculate percent yield of a reaction
  • Calculate the equilibrium constant of a reaction at a given temperature
  • Draw Lewis electron dot diagrams
  • Determine bond angles
  • Explain how polarity and intermolecular attraction would impact the outcome of a reaction and the states of its products

You only have a short amount of time for each free-response question (around 20 minutes for the long ones and 10 for the short ones), so you need to have all the information you learned in the course pretty well-mastered if you want to earn the majority of these points!

 

What Topics Does AP Chemistry Cover?

The AP Chemistry course is structured around nine major units, each of which includes multiple more specific topics. Your teacher might follow these units, or they may have their own order for presenting information. For more information on each of these units, check out our guide on AP Chemistry notes.

 

Unit 1: Atomic Structure and Properties

  • Moles and molar mass
  • Mass spectroscopy of elements
  • Elemental composition of pure substances
  • Composition of mixtures
  • Atomic structure and electron configuration
  • Photoelectron spectroscopy
  • Periodic trends
  • Valence electrons and ionic compounds

 

Unit 2: Molecular and Ionic Compound Structure and Properties

  • Types of chemical bonds
  • Intramolecular force and potential energy
  • Structure of ionic solids
  • Structure of metals and alloys
  • Lewis diagrams
  • Resonance and formal charge
  • VSEPR and bond hybridization

 

Unit 3: Intermolecular Forces and Properties

  • Intermolecular forces
  • Properties of solids
  • Solids, liquids, and gases
  • Ideal gas law
  • Kinetic molecular theory
  • Deviation from ideal gas law
  • Solutions and mixtures
  • Representations of solutions
  • Separation of solutions and mixtures chromatography
  • Solubility
  • Spectroscopy and the electromagnetic spectrum
  • Photoelectric effect
  • Beer-Lambert Law

 

Unit 4: Chemical Reactions

  • Introduction for reactions
  • Net ionic equations
  • Representations of reactions
  • Physical and chemical changes
  • Stoichiometry
  • Introduction to titration
  • Types of chemical reactions
  • Introduction to acid-base reactions
  • Oxidation-reduction (redox) reactions

 

Unit 5: Kinetics

  • Reaction rates
  • Introduction to rate law
  • Concentration changes over time
  • Elementary reactions
  • Collision model
  • Reaction energy profile
  • Introduction to reaction mechanisms
  • Reaction mechanism and rate law
  • Steady-state approximation
  • Multistep reaction energy profile
  • Catalysis

 

Unit 6: Thermodynamics

  • Endothermic and exothermic processes
  • Energy diagrams
  • Heat transfer and thermal equilibrium
  • Heat capacity and calorimetry
  • Energy of phase changes
  • Introduction of enthalpy of reaction
  • Bond enthalpies
  • Enthalpy of formation
  • Hess's Law

 

Unit 7: Equilibrium

  • Introduction to equilibrium
  • Direction of reversible reactions
  • Reaction quotient and equilibrium constant
  • Calculating the equilibrium constant
  • Magnitude of the equilibrium constant
  • Properties of the equilibrium constant
  • Calculating the equilibrium concentrations
  • Representations of equilibrium
  • Introduction to Le Chatelier's Principle
  • Reaction quotient and Le Chatelier's Principle
  • Introduction to solubility equilibria
  • Common-ion effect
  • pH and solubility
  • Free energy of dissolution

 

Unit 8: Acids and Bases

  • Introduction to acids and bases
  • pH and pOH of strong acids and bases
  • Weak acid and base equilibria
  • Acid-base reactions and buffers
  • Acid-base titrations
  • Molecular structures of acids and bases
  • pH and pKa
  • Properties of buffers
  • Henderson-Hasselbalch equation
  • Buffer capacity

 

Unit 9: Applications of Thermodynamics

  • Introduction to entropy
  • Absolute entropy and entropy change
  • Gibbs Free Energy and thermodynamic favorability
  • Thermodynamic and kinetic control
  • Free energy and equilibrium
  • Coupled reactions
  • Galvanic (Voltaic) and electrolytic cells
  • Cell potential and free energy
  • Cell potential under nonstandard conditions
  • Electrolysis and Faraday's Law

 

Tips for AP Chemistry Review

Throughout the year, and especially as you begin to study more for the AP exam in the spring, keep these tips in mind to keep your studying as effective and efficient as possible.

 

Tip 1: Start From the Beginning

Get your fundamentals straight before you try to do more complicated problems. On many AP Chemistry questions, you have to integrate a few pieces of essential knowledge and apply them to a given scenario. If you're shaky on the foundational concept, you won't be able to get to the correct answer. When you start studying, fill the gaps in your knowledge from earlier in the course first.

 

Tip 2: Redo Problems You Didn't Get the First Time

If you can't figure out a problem and have to look up the solution, don't just read over what you were supposed to do and leave it at that. Review the steps you should have taken to get the correct answer, and then, without looking at them, try to resolve the problem.

Learning by doing is very important in chemistry. Make sure you know why you're solving the problem a certain way. You should also reinforce your knowledge by going through other similar problems.

 

Tip 3: Do Lots of Free-Response Questions

You might be tempted to stick with practicing multiple-choice questions because you can do a lot of them quickly and feel like you've made significant progress. However, it's extremely important not to ignore the free-response section of the test in your studying if you want to do well. Free-response questions are a bigger challenge to your chemistry knowledge because you have to come up with the answers independently. Practicing them will help you do better on the test as a whole. If you can answer free-response questions correctly on a consistent basis, that means you really know your stuff!

body_freeresponsequestions.jpgThis is what's gonna happen if you don't practice free-response questions!

 

How to Review for AP Chemistry

Your AP Chemistry review should revolve around detecting your areas of weakness and practicing relevant problems. Here are the steps you might go through:

 

Step 1: Take and Score a Practice Test

The first thing you should do is take a full practice test to assess how well you know the material. It's more efficient just to study the concepts that you're still shaky on rather than going back through all your notes for the course. Make sure you take the test with the same time constraints as the real exam, and don't use a calculator on the multiple-choice questions.

You should also circle any questions where you feel even a little unsure of the correct answer. You need to go over those concepts even if you end up getting the question right so you can be as comfortable as possible with all the content. When you're done with the test, you can score it and set a goal for how much you want to improve.

 

Step 2: Categorize Your Mistakes (and Any Other Questions That You Were Unsure About)

Now that you've scored your test, go through your mistakes and lucky guesses, and sort them by topic area. This is the best way to get a clear picture of where you have the most significant issues with the content. Your list of mistakes will inform the rest of your review. I'd also recommend redoing problems that you missed to see if you can get to the correct answer.

 

Step 3: Review Relevant Content

If there was any essential background information on the test that you forgot, start by reviewing that content. The information that you learned in the first couple months of the course serves as a foundation for the rest of the class. After you feel confident with the basics, you can move onto studying higher-level topics. You might review your notes on how to solve certain types of problems or look back at the information in your textbook. You can also use an AP review book to study. Sometimes this is a better option because review books are specifically tailored to the test.

 

Step 4: Do Practice Problems

Reviewing content isn't enough in chemistry. You need to know how to apply your knowledge to unfamiliar experimental scenarios on the test. Spend some time doing practice problems that pertain to each of your areas of weakness until you feel more comfortable with the subject matter.

 

Step 5: Take Another Practice Test to See If You've Improved

After you finish doing practice problems, try out your new skills on another practice test. You can score the new test and see whether you're satisfied with your new (and hopefully improved) scores. You always have the option of repeating this process if there's still room for growth. If you don't see much improvement, you may have to go back and reevaluate your study methods.

If there are some concepts that you're having a really hard time wrapping your head around, I'd encourage you to ask your teacher or one of your classmates to help you understand the material better. Sometimes, if you can't figure something out yourself, an alternative explanation is what you need for it to click.

Here's an approximate time breakdown for all of these steps:

  • Take and score a practice test: 4 hours
  • Categorize your mistakes: 1 hour
  • Review content: 2 hours
  • Do practice problems: 2 hours
  • Take a second practice test: 4 hours

Total time for one cycle: 13 hours

 

body_journey.jpgNow it's time to set off on your own personal review journey. Good luck out there. No, I don't know why someone sculpted a ceramic frog with a rolling suitcase, but I have to assume that their life is much more interesting than mine.

 

Conclusion

The AP Chemistry exam covers a challenging set of concepts that require skills in math, factual recall, and analytical thinking. It's also one of the longest AP tests, lasting three hours and 15 minutes total. To recap, the types of questions on the test include:

  • 60 multiple-choice questions (90 minutes)
  • Seven free-response questions (105 minutes) made up of
    • Three long response (10 points each)
    • Four short response (four points each)

AP Chemistry has nine major units that encompass many more specific topics. The units are:

#1: Atomic Structure and Properties
#2: Molecular and Ionic Compound Structure and Properties
#3: Intermolecular Forces and Properties
#4: Chemical Reactions
#5: Kinetics
#6: Thermodynamics
#7: Equilibrium
#8: Acids and Bases
#9: Applications of Thermodynamics

 

Some study tips that I would recommend implementing as you prepare for the exam include:

  • Start with the basics
  • Redo problems that you miss
  • Practice free-response questions regularly

When you study, you follow these steps for the best results:

  • Take and score a practice test
  • Categorize your mistakes
  • Review content
  • Do practice problems
  • Take a second practice test

If you keep up with your classwork throughout the year and adhere to the advice in this article, you'll have no problem doing well on the AP test!

 

What's Next?

If you're thinking about buying a review book to supplement your in-class notes, check out my list of the best AP Chemistry review books.

Still planning out your schedule for the rest of high school? Read this guide for advice on which AP classes you should take based on your academic interests.

Are you considering taking an online AP class that your high school doesn't offer? Learn more about online AP classes and whether they're worth it for you.

 

Want to improve your SAT score by 160 points or your ACT score by 4 points? We've written a guide for each test about the top 5 strategies you must be using to have a shot at improving your score. Download it for free now:

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Samantha Lindsay
About the Author

Samantha is a blog content writer for PrepScholar. Her goal is to help students adopt a less stressful view of standardized testing and other academic challenges through her articles. Samantha is also passionate about art and graduated with honors from Dartmouth College as a Studio Art major in 2014. In high school, she earned a 2400 on the SAT, 5's on all seven of her AP tests, and was named a National Merit Scholar.



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