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AP Chemistry: Exam Prep17 chapters | 174 lessons | 10 flashcard sets

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Lesson Transcript

Instructor:
*Elizabeth (Nikki) Wyman*

Nikki has a master's degree in teaching chemistry and has taught high school chemistry, biology and astronomy.

Learn about the multiple choice section of the AP Chemistry exam and what to expect when you take the test. Learn tips for test preparation and strategies for test taking specific to this test.

Multiple-choice questions can be torturous. The answer is one of a few options sitting right in front of you, but it's not always clear which one it is! Don't worry though! If you carefully prepare yourself and use some helpful strategies during the test, you can be more confident that you are choosing the right answer.

The AP Chemistry multiple-choice section is 60 questions and 90 minutes long. This section will count towards 50% of your exam score. You will be provided with a periodic table and formula and constants chart. You will not be allowed to use a calculator. Each question will have four answers (A-D), and there is no penalty for wrong answers! Super cool!

The questions are all based on the six big ideas identified and described in the AP chemistry course description, available to download on the AP Central Chemistry Exam website. Big ideas are based on:

- Atomic structure and theory
- Intermolecular forces, particle attractions, and properties of matter
- Chemical reactions
- Kinetics
- Thermodynamics
- Equilibrium

It would be fair to expect an equal number of questions from each Idea. Ideally, you would master each Idea before going into the test. Realistically, though, that is a monumental undertaking. If you encounter questions you are not familiar with or don't understand, don't be too hard on yourself and move on to something you know.

There are two types of multiple-choice questions you are likely to see. **Discreet item** questions consist of a single question with four answers (A-D).

Here's example of a discreet item question:

1. Aniline (C5H5NH2) is a weak base with a Kb of 4 x 10^-10. The pH of a 1 M solution of aniline is in the range of:

(A) 5-6

(B) 7-8

(C) 9-10

(D) 12-13

This is the only question we have on the given information.

**Item sets** consist of two or more test questions each with four choices (A-D). The questions in the set are based off a data set, a graph, an experiment or another type of stimulus.

Here's an example of a two item set question:

Consider the Lewis dot diagrams for BF3 and ammonia:

2. The molecular geometry of the two substances are:

(A) The same because they each have three bonding electron domains

(B) Different because they have three different numbers of electron domain and different electron domain geometries

(C) The same because nonbonding electron domains do not affect geometry of bonding domains

(D) Different because Boron is violating the octet rule

The second question pertaining to those Lewis dot structures is:

3. The bond angles between hydrogens and nitrogen are:

(A) Greater than the bond angles between oxygen and hydrogen because of the repulsive force of the lone pair

(B) Less than the bond angles between oxygen and hydrogen; the repulsive force of one lone pair is less than that of two

(C) The same as bond angles between oxygen and hydrogen because they have the same electron domain geometry

(D) Dependent on the amount of kinetic energy in the system

In this case, both questions are based on the Lewis dot structures for BF3 and Ammonia (NH3).

If you're enrolled in AP Chemistry, you're likely doing plenty to prepare for the test already! It's always a good idea to practice AP style multiple-choice questions as much as possible, so you get used to the format, the rigor and the question styles. You can find practice questions on the AP Central Chemistry Exam website. Seek out questions that pertain to your current and past topics. These questions are extremely similar to questions on the actual test. I highly recommend using these as a study tool.

Additionally, it is helpful to get an AP Chemistry review book. Be careful to get a version generated for the 2013/14 year or after because these versions are designed for the new AP curriculum. These review books organize material into important topics and provide multiple-choice questions. Some of these questions are not the same caliber as the ones on the AP test itself.

During the test, you will have use of an AP-issued periodic table and chart that includes formulas and constants. You can print the same versions you will be using on the test today! In fact, you should do this immediately after finishing this video.

Become familiar with the formulas and constants on the chart months before you take the test, where they are and what they mean. Definitely take the time to understand the appropriate units for each formula or constant. Units can be your most helpful ally when solving tricky problems.

It's not a good idea to walk into the test assuming all of the items on the chart will be familiar and helpful. If you don't know Coulomb's law before the test, glancing at the equation won't help you! Plus, you might end up wasting precious time trying to understand formulas on the chart.

Practice taking the multiple-choice segment of the test. Again, you can find practice tests for former AP Chemistry tests on the AP Central Chemistry Exam website. Set a timer for 90 minutes, gather your periodic table and chart and get to work! Practice the test taking strategies discussed in the next segment.

Second to studying, taking care of yourself is probably the most important thing you can do to prepare for the test. Make sure that you:

- Get at least eight to ten hours of sleep (at least the night before, if not as much as possible).
- Eat breakfast and bring a snack. Your brain consumes an awesome amount of calories, especially during a 3-hour test!
- Dress in layers.
- Bring pencils and a calculator (for the FRQ portion). Make sure your batteries work.

The test booklet is yours for a precious 90 minutes. Don't be afraid to:

- Scratch answers out
- Underline or circle valuable information
- Write equations
- Make notes on the test

Remember, you will not be graded on any of the work done in the booklet. All answers must be recorded on the answer sheet. Time management on the test is paramount to success. To figure out how to best manage your time, let's do some math.

You have 60 questions and 90 minutes; that means 1.5 minutes per question. You could go through the test once and spend 1.5 minutes on each question. This is a tricky method because sometimes we get stuck on certain questions or get panicky if we don't know the answers to the first few questions.

AP Central recommends a different strategy that involves spending less time on questions initially and going through the test three times. The first time you go through the test, spend approximately 40 seconds on each question. Don't know what 40 seconds feels like? When you're practicing multiple-choice questions at home, set a timer for 40 seconds and put it on repeat. Hopefully, this time will register with you. During the test, you can look at your watch or the clock, but this can become a little burdensome.

For questions that you can't finish in 40 seconds, circle the number and move on. For questions that you don't know how to answer at all, mark with an X. If you are struggling with these questions, it is not worth sacrificing your time trying to figure them out if you could be answering questions you do know the answers to.

After you've gone through the test once, go back through and focus on the questions you circled. If you finish these questions and there is time remaining, go through the test again and focus on the questions you marked with an X.

As mentioned earlier, there is no penalty for wrong guesses! On the questions you absolutely don't know, it is still worth your time to guess and guess well. When working through these questions, try to eliminate two answers and then make your guess.

As with any test, make sure to read questions and answers carefully. Students often pick the first answer that seems best. Taking the time to read all answers is worth your while. Also, be 100% sure that you know what the question is asking. Occasionally, a question will include information that is supplemental but not essential. This kind of extra information can interfere with a student's understanding of what the question is asking.

Much of the AP questions are conceptual and involve critical thinking, but that doesn't mean you won't encounter some math on the test. Because you can't use a calculator, most questions can be answered by making estimations and employing your hard-earned math skills.

When you encounter a math problem, make sure you identify your given quantities, your desired quantities and the relevant conversion factors. Always, always, always include units. Next, determine what kind of formula you'll need to solve the problem. Either pull this formula from memory or refer to your formula chart. If you're stuck trying to figure out what to do, look at the units from your given quantity and desired quantity. Find formulas that involve those units.

When solving these problems, it's okay to round, estimate and approximate. You can save a lot of time dividing 10 into 100 versus 9.6 into 100. If you cannot arrive at an answer close to any of the options, check your math and how much you estimated or approximated.

Have a grasp of the following mathematical concepts and processes:

- Significant figures
- Scientific notation
- Multiplying and dividing with decimals
- Shortcuts for operations involving exponents
- Quick conversions for common changes of units (J --> kJ, mL --> L)
- Algebraic operations

Let's look at a problem shown earlier - the one about aniline.

Aniline (C5H5NH2) is a weak base with a Kb of 4 x 10^ -10. The pH of a 1 M solution of aniline is in the range of:

(A) 4-5

(B) 6-7

(C) 9-10

(D) 12-13

This question is asking us to identify pH of a weak base. We know that aniline has a Kb value of 4 x 10^-10 and that it is a 1 M solution. We know that pH is determined by concentration of hydrogen ions. If we know the concentration of hydroxide ions or pOH, then we can determine pH. I know that Kb can get me to hydroxide concentration, and from there I can determine pH.

We know that aniline will generate two products, OH^- and C5H5NH3^+. We also know that since it's a weak base, this will only happen a very small amount of the time.

In case we've forgotten specifics about Kb, the formula chart has exactly what we're looking for!

Kb = [OH-][HB+]/[B], in our case Kb = [OH-][C5H5NH3+]/[C5H5NH2]

I can substitute 1 M for the concentration of C5H5NH2, set Kb equal to 4 x 10^-10 and set both [OH-] and [C5H5NH2] equal to *x*.

The equation becomes 4 x 10^-10 = x2/1 M. The 1 M is something I can safely ignore because anything times one is itself. If this was a number that was different from 1 by a factor of 10, I would consider those effects in relation to my Kb value.

Now it's onto the square root of 4 x 10^-10. It's easiest to call this number 1 x 10^-10. Remember, if you do this, your answer will be a tiny bit lower (we're talking tenths here) than the actual answer. Since our answers give a range of pH values, this is an okay move.

If you know your rules for exponents, you know the square root of 1 x 10^-10 is 1 x 10^-5. Since pH and pOH are on a logarithmic scale, pOH is approximately the magnitude of the exponent. Thus, pOH is 5. This equates to a pH of approximately 9 (plus a few tenths of a pH to compensate for the approximations that we did earlier). The answer for this question would be (C).

The multiple-choice section consists of:

- 60 questions
- 90 minutes
- Each question has four answer options (A-D)
- There will be
**discreet items**and**item sets** - There is no penalty for wrong guesses!

Keep in mind that this portion of the test:

- Counts for 50% of the exam score
- Periodic table and formula and constant chart is provided
- No calculators are allowed

Start preparing for the exam months in advance. Practice AP style multiple-choice questions, become familiar with the formula and constant chart, take practice tests and of course, study the content.

Take care of yourself before the test and arrive prepared! When taking the test, plan to go through the test three times. The first time, give yourself 40 seconds a problem. Mark problems that you can't finish in under 40 seconds by circling the number. Attempt these questions your second time through. Mark problems that you don't know how to do with an X. Attempt these questions your last time through.

On math-based problems, it is okay to estimate, round or approximate. Make sure you are familiar with the following concepts and processes:

- Significant figures
- Scientific notation
- Multiplying and dividing with decimals
- Shortcuts for operations involving exponents
- Quick conversions for common changes of units
- Algebraic operations

Once you've completed this lesson, you should be able to:

- Describe the structure and content of the multiple-choice section of the AP Chemistry exam
- Identify the two question types you will see on this exam
- Describe general considerations and an effective test-taking strategy for the exam
- Explain the concepts you should be familiar with for the math-based questions

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AP Chemistry: Exam Prep17 chapters | 174 lessons | 10 flashcard sets

- AP Chemistry Exam Scoring Information
- How to Master Multiple Choice Questions on the AP Chemistry Exam 13:36
- How to Master the Free Response Section of the AP Chemistry Exam 9:40
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