AP® Chemistry Crash Course, Book + Online: Get a Higher Score in Less Time

PART I

INTRODUCTION

Chapter 1

Keys for Success on the AP® Chemistry Exam

The textbooks typically used in college-level general chemistry courses contain thousands of facts and concepts packed into (at least) several hundred pages. If the AP® Chemistry exam were to test all of that information, earning a good score on the exam would be a daunting task.

Studying for the AP® Chemistry exam requires you to be a pragmatic learner who can distinguish the important (tested) material from the material that is merely interesting to know. This Crash Course will help you to become more focused and efficient in your exam prep. Your chances of scoring well on the exam will be enhanced by pinpointing what is absolutely necessary and ignoring the fluff. The keys to success include the following:

The AP® Chemistry course and exam are based on the content of an introductory chemistry course taught at the college level. The topics taught in AP® class reflect major topics found in a number of college-level textbooks. The course also includes some inquiry-based laboratory situations, application of what the College Board calls scientific practices, and chemical calculations.

To succeed in the course, students must master the basic concepts of chemistry and apply these concepts to various situations in a traditional test format.

In May 2019, the College Board reorganized the AP® Chemistry course and exam framework around four big ideas and nine units.

The content of the course and exam is now based on the following four big ideas:

1.Big Idea 1: Scale, Proportion, and Quantity (SPQ)

Quantities in chemistry are expressed at both the macroscopic and atomic scale. Explanations, predictions, and other forms of argumentation in chemistry require that you understand the meaning of these quantities, as well as the relationship between quantities at the same scale and across scales.

2.Big Idea 2: Structure and Properties (SAP)

Properties of substances observable at the macroscopic scale emerge from the structures of atoms and molecules and the interactions between them. Chemical reasoning moves in both directions across these scales. Properties are predicted from known aspects of the structures and interactions at the atomic scale. Observed properties are used to infer aspects of the structures and interactions.

3.Big Idea 3: Transformations (TRA)

At its heart, chemistry is about the rearrangement of matter. Understanding the details of these transformations requires reasoning at many levels as you must quantify what is occurring both macroscopically and at the atomic level during the process. This reasoning can be as simple as monitoring amounts of products made, or as complex as visualizing the intermolecular forces among the species in a mixture. The rate of a transformation is also of interest, as particles must move and collide to initiate reaction events.

4.Big Idea 4: Energy (ENE)

Energy has two important roles in characterizing and controlling chemical systems. The first involves accounting for the distribution of energy among the components of a system and the ways that heat exchanges, chemical reactions, and phase transitions redistribute this energy. The second looks at the enthalpic and entropic driving forces for a chemical process. These are closely related to the dynamic equilibria present in many chemical systems and the ways in which changes in experimental conditions alter the positions of these equilibria.

The AP® Chemistry course content is organized into the following nine units. This unit structure provides one possible sequence for teaching the course.

Unit 1: Atomic Structure and Properties

Unit 2: Molecular and Ionic Compound Structure and Properties

Unit 3: Intermolecular Forces and Properties

Unit 4: Chemical Reactions

Unit 5: Kinetics

Unit 6: Thermodynamics

Unit 7: Equilibrium

Unit 8: Acids and Bases

Unit 9: Applications of Thermodynamics

In many ways, this new course framework is geared toward your teachers to guide them in planning your AP® course. But this book is written particularly for you to use as a resource throughout the school year and as a refresher in the run-up to the exam.

In the chapters that follow, you will find content-specific help for all topics covered in the College Board’s new course framework, as well as tips for success and strategic insight into what you need to know for the AP® Chemistry exam as it will be given in 2020 and beyond.

To complement your AP® coursework, reviewing the corresponding Crash Course chapters is a great way to reinforce what you’ve learned in class. The following table offers a quick look at how this book covers the new unit structure.

Where You’ll Find the AP® Chemistry Units in This Book

The AP® Chemistry exam is 3 hours and 15 minutes in length and consists of a 90-minute multiple-choice question section and a 105-minute free-response question section. There are 60 multiple-choice questions and 7 free-response questions.

Section I. 60 multiple-choice questions (90 minutes)—50% of the grade

In this section of the exam, no calculator is allowed, but access to the periodic table and an equations and constants sheet is allowed.

Ultimately, only 50 of these questions are counted in the final score (10 of them are used for College Board statistical analysis only, but you are not told which ones they are, so you should concentrate on trying to answer all 60 correctly).

Section II. 7 free-response questions (3 long questions and 4 short questions, all with multiple parts) (105 minutes)—50% of the grade

In this section of the exam, a calculator is allowed along with access to the periodic table and an equations and constants sheet.

Multiple-choice questions test the knowledge, understanding, and application of the big ideas and science practices covered in the AP® Chemistry course. Let’s try an example:

When the chemical equation below is completed and balanced, what statement best describes the reaction?

C5H12(g) + O2 (g) → ?

(A)1 mole of pentane is consumed and 6 moles of water are produced.

(B)1 mole of pentane is produced and 6 moles of water are consumed.

(C)1 mole of pentane is consumed and 1 mole of water is produced.

(D)1 mole of pentane is produced and 1 mole of water is consumed.

The correct answer is (A). The equation represents a combustion reaction that will produce carbon dioxide and water. When balanced, the equation is:

C5H12(g) + 8O2(g) → 5CO2(g) + 6H2O(g)

It is essential to know these basic ideas when confronted by this type of question. This book will give you the content that you need to know to successfully answer the questions.

In addition, calculation-based chemistry questions are also part of this section. However, since no calculator is allowed, some multiple-choice questions will ask you to select the correct mathematical setup, or require you to do some simple arithmetic or estimation. Here’s an example:

At 25°C, 300 milliliters of an ideal gas exerts a pressure of 740 mm Hg. What is the volume of the gas under conditions of 0°C and 760 mm Hg?

(A)2.68 mL

(B)26.8 mL

(C)268 mL

(D)2680 mL

The correct answer is (C). Using the combined gas law formula, remembering to convert temperatures to Kelvin and plug in values, the following mathematical setup is determined:

Solving for V2 gives

Even though you have no calculator, you should see that 300 mL is being multiplied by two numbers that are slightly less than 1

and, as such, the answer must be slightly less than 300 mL; 268 mL is the correct answer choice. Estimation should allow you to find the correct answer without the need for a calculator (i.e., without the need to find the exact answer).

Multiple-Choice Question Formats

There are two types of multiple-choice questions that make up the majority of Section I of the AP® Chemistry exam, with Type II accounting for as much as 50% of the exam.

Question Type I presents traditional multiple-choice questions with four answer choices: (A) through (D). There is only one correct answer. For example:

Atoms of element X have the electron configuration shown below.

1s²2s²2p⁶3s²3p⁴

The compound most likely formed with lithium, Li, is

(A)LiX

(B)LiX2

(C)Li2X

(D)LiX3

The correct answer is (C). A lithium ion has a charge of +1. Element X will have an ion with a charge of –2, and the ions must combine to give a compound with no overall charge.

Question Type II presents two to six questions preceded by a single stimulus or set of data, and typically includes a paragraph or two of text. Once again, there is only one correct answer for each question. For example:

Questions 26–28

The chemical reaction between sodium metal and chlorine gas can be represented by the equation shown below.

Na(s) + ½ Cl2(g) → NaCl(s)

ΔH = negative (i.e., it is an exothermic reaction)

The reaction can be broken down into a number of individual processes, including:

Atomization (sublimation) of sodium

First ionization energy of sodium

Atomization of chlorine

First electron affinity of chlorine

Lattice energy of sodium chloride

26.Which of the following represents the first electron affinity of chlorine?

(A)Cl(g) + e– → Cl–(g)

(B)Cl–(g) + e– → Cl²–(g)

(C)Cl(g) → Cl+(g) + e–

(D)Cl2(g) → 2Cl(g)

The correct answer is (A). The equation in (A) represents the definition of first electron affinity.

27.What is the expected energy change when chlorine gas is produced by the decomposition of NaCl?

(A)Exothermic, energy is released

(B)Exothermic, energy is absorbed

(C)Endothermic, energy is released

(D)Endothermic, energy is absorbed

The correct answer is (D). The reverse of the exothermic reaction in the question is the decomposition reaction, and the reverse of an exothermic process is endothermic. Endothermic reactions absorb energy from the surroundings.

28.If 22.99 g of sodium and 35.45 g of chlorine gas are combined in a vessel and the reaction goes to completion, what will the contents of the vessel contain at the conclusion of the reaction?

(A)Na only

(B)Na, Cl2, and NaCl

(C)NaCl only

(D)Cl2 only

The correct answer is (C). The masses given are in the exact molar stoichiometric ratio given in the balanced equation, meaning each reactant is completely consumed, leaving only the product.

The free-response questions fall into two categories: long and short. Three long questions should take 15–20 minutes each to answer, and four short questions should take 7–10 minutes each to answer, but you are free to divide your time up as you see fit. All seven of the free-response questions have multiple parts.

In this section of the exam, expect to see an emphasis on science practices and laboratory situations, and on particulate diagrams and models used to represent reactions and concepts at the molecular level.

Section I. Scores on the multiple-choice section of the exam will be based on the number of questions answered correctly. Points are not deducted for incorrect answers, and no points will be awarded for unanswered questions.

Section II. Scores on the free-response section are weighted and then combined with the multiple-choice score to give a score out of 100.

The raw score is converted to a composite score of 5, 4, 3, 2, or 1. An AP® score of 5 is approximately equivalent to the average score of a college student who gets an A in an equivalent college chemistry course. A score of 4 is approximately equivalent to college grades of A–, B+, and B, and a score of 3 is approximately equivalent to college grades of B–, C+, and C.

The College Board describes the AP® grades as follows:

5 Extremely Well Qualified

4 Well Qualified

3 Qualified

2 Possibly Qualified

1 No Recommendation

The data above indicates that typically about one out of every ten students who takes the AP® Chemistry exam earns a 5, while staggeringly, almost one out of every two students does not receive a qualifying score, which would be 3 or higher. This Crash Course is tailored to help you earn the highest grade possible on the exam.

This Crash Course contains everything you need to know to score well on the AP® exam. You should, however, supplement it with materials provided by the College Board and from your teacher and class. The AP® Chemistry Course and Exam Description (CED) and released AP® Chemistry exams can all be found at AP® Central.

PART II

CONTENT REVIEW

Chapter 2

Atoms and Moles

A. Atoms, Compounds, Ratios, and Masses

1.All matter is composed of atoms.

2.There are a limited number of different types of atoms; each different type of atom is an atom of a different element. The elements are organized on the periodic table.

3.A large number of atoms of a single element always has the same average mass.

4.Atoms can combine to form compounds.

5.A pure compound always has the same whole-number ratio of different atoms, e.g., water is always H2O, and because of #3 above, the ratio of the masses of the elements is always the same in any given compound.

6.If the whole-number ratio of the atoms (and, therefore, the ratio of the