Cracking the AP Chemistry Exam

Part III

Test-Taking Strategies for the AP Chemistry Exam

Chapter 2

How to Approach Free-Response Questions

OVERVIEW OF THE FREE-RESPONSE SECTION

Section II is composed of 7 free-response questions. You will be given 90 minutes to complete this section, which is worth 50 percent of your total score.

The first three free-response questions are longer, and are worth 10 points each. The College Board recommends you take about 20 minutes per question on these. The last four questions are much shorter, and only worth 4 points each. For these, the College Board recommends you take about 7 minutes each.

The suggested times are just that, suggestions-your results may vary based on how comfortable you are with the topic being tested within each question. They do give you a good guideline though. You probably shouldn’t be spending more than about 20 minutes on any of the first three questions. Don’t be afraid to cut yourself off and come back to questions later if time allows.

CRACKING THE MATH PROBLEMS

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 ensure 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.

Remember Significant Figures

You can lose 1 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 complete only 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 3!

STRATEGIES FOR CRACKING THE FREE-RESPONSE SECTION

This section is here to test whether you can translate chemistry into English. Most of the questions can be answered in two or three simple sentences, or with a simple diagram or two. Here are some tips for answering the seven free response questions on Part II.

Show That You Understand the Terms Used in the Question

If you are asked 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.

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.

Graders Will Follow Your Reasoning, Even If You Make 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 favorability, as long as your answer in (c) is correct based on an exothermic reaction.

REFLECT

Respond to the following questions:

·        How much time will you spend on the short free-response questions? What about the long free-response questions?

·        What will you do before you begin writing your free-response answers?

·        Will you seek further help, outside of this book (such as a teacher, tutor, or AP Central), on how to approach the questions that you will see on the AP Chemistry exam?