CLEP / Chemistry

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  • REA CLEP Chemistry

REA CLEP Chemistry

*At the time of publishing.


So you want to CLEP out of your Chemistry classes in college…Brilliant!! Everybody hates chemistry anyway, right? So let’s get down to business and help you navigate the choppy waters of CLEP Chem (normally worth 6 credit hours). Maybe you’ll even learn to like it!

The study guide section is broken into the nine sections given on the CLEP chemistry website. Each of the sections comprises a certain percentage of the CLEP exam and this guide will loosely follow those percentages.

Fast Chemistry Study Guide

Many of these topics require you to solve a mathematical problem—this normally involves applying the appropriate equation to get the correct answer. This guide will help you to know which equations to use for certain topics—it would be a good idea to develop a list of these equations that you just have to know (memorize).

Some of you may continue with your chemistry education—topics that you will repeatedly see in future classes (particularly for Organic Chemistry) are written in bold. It is highly recommended that you take some extra time with these topics during your preparation.

So Let’s Roll!

States of Matter (19%)

Liquids, Solids and Gases.

Gases are simple—you need the Ideal Gas Law (know it!). Also, you should know the postulates of Kinetic Molecular Theory (boring as snot, but write them down). Also get the equation for KMT—all of this should be in Chapter 5.

Liquids and Solids—Normally around Chapters 10 or 11. You’ll need to understand why they form, so really focus on INTERMOLECULAR FORCES!! Look at phase diagrams (which separate liquids, solids and gas of a substance as a function of temp and pressure). Water is unusual, know these.

Solutions—lots of definitions (solute, solvent, solution) and lots of different ways to express concentration (molarity, molality, %, ppm, ppb). Know how to do these (get the equations).

Colligative properties—more equations here…get them and know how to use them. Note: the number of particles is important! NaCl? Makes Na+ and Cl–, so it makes TWO particles. Ionic substances break apart into multiple particles.

Structure of Matter (20%)

Know the three atomic particles of the atom and the four guys most responsible for developing atomic theory (proton, electron and neutron; Dalton, Rutherford, Thomson and Millikan; respectively).

Isotopes, mass number and atomic numbers…easy.

The structure of atoms gives us the following: electron energy levels, atomic spectra (hydrogen line spectra) quantum numbers and atomic orbitals (spheres, dumbbells and cloverleafs for s, p and d orbitals, respectively. Q#’s and AO’s are related—spend some time with these. EQUATIONS!! Relating frequency/wavelength to speed of light. The energy of a photon of energy (using Planck’s constant). Go get these equations…now.

Periodic trends—Use the graphic below as a guide (Table 1). NOTE—Atomic radius decreases from left to right (even though the atomic number increases). That’s a tricky one!

BONDS!! Chemical Bonds!

THE MOST IMPORTANT TOPIC in General Chemistry!! Molecular structure dictates molecular properties. In essence, this IS chemistry. Pay attention to this topic, learn it well.

Differentiate between ionic, covalent and polar covalent bonds

Ionic bonding as it relates to the size of an ion (cations get smaller, anions get larger)

For Covalent Molecules—Lewis structures (REALLY take time to learn these!) -# VE
-basic structure
-formal charge
Determine electron group geometry
Determine molecular geometry (at a central atom) for 3, 4, 5 and 6 electron groups
Distinguish between s and p bonds
Determine the hybridization at a central atom
-based on the number of electron groups
-spxdy notation for the above

Reaction Types (12%)

These all come from a typical “Chapter 4” and the “Electrochemistry” chapter towards the end of a textbook.

Acid-Base Chemistry—simple definitions (THIS SUBJECT WILL FOLLOW YOU THROUGHOUT YOUR CHEMISTRY CAREER!!). Learn the difference between Strong/Weak (definition). Learn the strong acids (seven of them) and the strong bases (metal hydroxides like NaOH).

Precipitation and Redox reactions are pretty simple—Learn the “solubility rules” for predicting the formation of a solid (a precipitate). Also called ‘double displacement’ reactions.

Electrochem stuff—learn how to calculate an oxidation number (for water, it’s +1 for H and –2 for oxygen). Learn how to do these things for any atom in any molecule.

Now go to the Electrochem chapter and get the equations involving E0cell. There will be a bunch of them. The Nernst equation, the relationship to the equilibrium constant and to free energy (DG—we’ll get to that in a bit). Learn how to use these equations.

Equations and Stoichiometry (10%)

Holy moly, do you need to learn THIS!! But for stoichiometry, you need only one equation—grams to moles to moles to grams. Learn to manipulate this one thing and you’ll be WAY ahead of the game. Grams of A—moles A—moles B—grams B. Grams to moles (and moles to grams) uses the molecular mass of the different substances while moles—moles uses the balanced chemical equation.

Shamelessly manipulate the above to do simple stoichiometry, limiting reactant, theoretical yield and % yield problems.

Equilibrium + Kinetics (11%)

More equation and math-intensive chapters here. Go to the end of each chapter and copy down the equations in the summary section. For Kinetics, learn anything with the term ‘rate’, rate law, rate constant, reaction order (all experimentally derived). Get the Arrhenius equation (the effect of temp on the reaction rate) so you can calc activation energies (always positive numbers).

Equilibrium requires you to memorize the K equation (products over reactants). Go get that general equation and commit it to memory. You’ll have to calculate the following types of equilibrium constants—Ka, Kb, Kc, K, Kw, Ksp. There are several later chapters that cover each of these…you’ll need them.

Other equilibrium equations? BUFFERS!! Another topic that will follow you up the chemistry food chain. Henderson-Hasselbach—go find that equation right now and learn how to use it.

Thermodynamics (5%)

Typically two chapters (normally 6 and 17)—one simple equation for all three variables (DH, DS and DG). Sum of the products – sum of the reactants. There’s also G = H – T(S). Learn this one too.

For H (enthalpy), learn what the signs mean! Exothermic (negative sign, heat is released), endothermic (positive, heat consumed…colder). For G, negative = spontaneous. For S, + means more disordered. This is a lot of information for a very small part of the exam.

Descriptive Chemistry + Experimental Chemistry (23%)

Once you’ve made it this far, there are a few chapters in the back of most textbooks that begin to apply you’ve learned (that’s the descriptive chem).

For the Descriptive Chemistry Chapters (Organic, Coordination Chemistry, Biochemistry, Nuclear Chemistry, Main Group Chemistry)—go to the SUMMARIES at the end of each chapter and take some notes there. They’re actually quite interesting.

Nuclear Chemistry—learn the balancing of the nuclear reactions (alpha and beta particles).

For “Experimental Chemistry”, there’s nothing you can really “study” for specifically. You can find some traditional experiments online and the typical equipment used in these experiments to work through this part…but if you haven’t had the ‘lab’ part, perhaps focus more on the other subjects.

Chemistry Free Practice Test

So, are you ready to test the waters? Take this practice quiz and judge your preparation level before diving into deeper study. All test questions are in a multiple-choice format, with one correct answer and four incorrect options. The following are samples of the types of questions that may appear on the exam.
Question 1: How many protons does an atom of silver contain?

  1. cannot determine this due to isotopic variation among silver atoms
  2. 47
  3. 61
  4. 108

Correct Answer: B. 47

Explanation: The other answers are at least plausible as 108 represents the atomic mass of silver and 68 represents the difference between atomic number and atomic mass (the number of neutrons). There IS isotopic variation in most atoms, but that doesn't change the atomic number (number of protons).

Question 2: What is the pressure exerted by 1.0 mol of an ideal gas at 25 °C in a 125 mL flask?

  1. 16.4 atm
  2. 0.196 atm
  3. 0.0164 atm
  4. 196 atm

Correct Answer: D. 196 atm

Explanation: This problem comes from the ideal gas law (PV = nRT). Temperature needs to be expressed in Kelvin, not C. Answers a and b both plug 25 °C into that expression. Volume needs to be expressed in L, not mL. Only d uses the correct units for all variables.

Question 3: Predict the precipitation product from the following displacement reaction

  1. No reaction occurs
  2. Ca3(PO4)2
  3. CaPO4
  4. NaCl

Correct Answer: B. Ca3(PO4)2

Explanation: While two answers represent calcium phosphate, only one has the correct ratio of these ions.

Question 4: The reaction of sodium metal with water produces hydrogen gas, sodium hydroxide and heat. This process is exothermic/endothermic and the sign of the DHrxn is +/–?

  1. Endothermic, sign is -
  2. Endothermic, sign is +
  3. Exothermic, sign is -
  4. Exothermic, sign is +

Correct Answer: C. Exothermic, sign is -

Explanation: Any thermochemical process that releases heat to the surroundings (as this one does) is exothermic and the calculation for the DHrxn would then be negative.

Question 5: Which of the following is the strongest Bronsted acid?

  1. H2O
  2. H2S
  3. H2Te
  4. H2Se

Correct Answer: C. H2Te

Explanation: Periodic trends in the acidity of binary hydride compounds increase as you go from the top to the bottom of a group on the periodic table. The ability of the conjugate base to stabilize the negative charge that forms with the loss of the H+ ion is the key. The ions formed when all of these compounds lose a H+ get larger as you go down a group; that larger volume helps stabilize the resulting anion.

Question 6: Which of the following elements has the largest second ionization energy?

  1. Al
  2. None of the above - they all have the same second ionization energy
  3. Mg
  4. Na

Correct Answer: D. Na

Explanation: Why? The second ionization of sodium requires the removal of a core electron. Core electrons require significantly more energy to remove than valence electrons. The electrons removed from Mg and Al are only valence electrons.

Question 7: Which of the following elements has the largest atomic radius?

  1. Si (atomic number 14)
  2. Cl (atomic number 17)
  3. P (atomic number 15)
  4. Ar (atomic number 18)

Correct Answer: A. Si (atomic number 14)

Explanation: Why? The lowest atomic number corresponds to the fewest number of protons in the nucleus. This deficiency exerts the lowest “Effective Nuclear Charge” on the valence electrons to attract them closer to the nucleus. This result is counterintuitive—most people think that atoms get larger as the atomic number increases.

Question 8: What is the orbital hybridization of carbon atoms in a diamond? In graphite?

  1. sp2, sp2
  2. sp3, sp3
  3. sp2, sp3
  4. sp3, sp2

Correct Answer: D. sp3, sp2

Explanation: The structure of a diamond is an interconnected network of carbon atoms covalently bound to four other carbon atoms. To form four bonds, a carbon atom has to hybridize four atomic orbitals. In doing so, it has to hybridize the s orbital and all three p atomic orbitals (s, p, p, p = sp3). Carbon atoms in graphite bind to three other carbon atoms (and thus require only three atomic orbitals—s, p, p = sp2).

Question 9: Which term is used to describe the change from the solid to the gaseous state?

  1. Vaporization
  2. Freezing
  3. Sublimation
  4. Condensation

Correct Answer: C. Sublimation

Explanation: There are six changes in phases of matter (solid to liquid, solid to gas, liquid to gas and the reverse processes). Directly converting from solid to a gas is called sublimation (most people know this as dry ice—carbon dioxide, at –77 °C, changes from a solid to a gas without becoming a liquid—hence the term “dry” ice).

Question 10: The freezing point of helium is –270 °C. The freezing point of xenon is –112 °C. Both elements are noble gases. Which of the following statements is supported by these data?

  1. Helium forms highly polar molecules
  2. The London dispersion forces between helium atoms are less than the London dispersion forces of the Xenon molecules
  3. The London dispersion forces between helium atoms are greater than the London dispersion forces between Xenon molecules.
  4. As the molecular weight of the noble gas increases, the freezing point decreases.

Correct Answer: B. The London dispersion forces between helium atoms are less than the London dispersion forces of the Xenon molecules

Explanation: Two answers are designed to be obviously wrong. Helium doesn't form molecules of any type. In one, the ‘molecular' weight is wrong. It's ‘atomic weight', not molecular. Either way, the freezing point doesn't decrease anyway. Dispersion forces have everything to do with physical properties of noble gases. Xenon has significantly higher dispersion forces than helium.

More CLEP Chemistry Study Resources

Looking for a study guide to fill a couple gaps, or just want a full length practice exam? You can find a few of my favorite resources below. Note that some of the links are affiliate – meaning I’ll make a few dollars if you purchase, but I’m only sharing those resources that were genuinely helpful during my own CLEP journey.
Official CLEP Study Guide

While quite short on the study side of things, the official CLEP book is the go-to final practice test. Since this is the only official practice test available, I normally use it as my final spot check before taking the test.

REA CLEP Chemistry

REA offers a great combination of CLEP study tips, exam study materials, and detailed practice tests. This book functions well as the central pillar of a strong CLEP prep strategy, with resources like the Official CLEP Study Guide (above) providing a great final practice test at the end.

InstantCert Academy

The website looks like it was made before the internet, but it’s legitimately the single most useful study guide I’ve found yet. Basically it’s a series of flashcards that help you study in a fast paced and fun way.

Plenty of other resources exist – just do a quick internet search – but these are the three that I’ve personally found the most helpful back when I did CLEP.