AP Chemistry Exam – Facts to Know

Review important chemistry facts before you take the AP chemistry exam. (Stephan Stefancik)
Review important chemistry facts before you take the AP chemistry exam. (Stephan Stefancik)

Before you take the AP Chemistry Exam (Advanced Placement Chemistry Exam), it’s helpful to review facts you need to know for the test. These facts are also helpful if you are studying for any other high school or college cumulative chemistry test.

About the AP Chemistry Exam

You don’t have to take the AP chemistry course in order to sit the exam. The test consists of two parts:

  • 75 question multiple choice test (90 minutes)
  • 6 question open-ended section (95 minutes)
  • Part A of this section is 3 questions (55 minutes), calculator permitted
  • Part B of this section is 3 questions (40 minutes), no calculator allowed

Topics Covered on the AP Chemistry Exam

You need to be familiar with the following topics:

chemical reactions (35-40%)
states of matter (20%)
structure of matter (20%)
descriptive chemistry (10-15%)
laboratory chemistry (5-10%)

Need To Know Facts

Here’s a (relatively random) list of important facts you need to know for the AP chemistry exam.

  • Use the full atomic masses provided on the periodic table for your calculations.
    You can’t get full credit for an answer if the grader can’t read your handwriting!
    Units are more likely to trip you up than anything else! For example. when using PV=nRT, if R is 0.0821, you need to use pressure in atm, volume in L, and temperature in K.
  • Trends or periodicity on the periodic table do not explain phenomena. They may be used to predict it.
  • Net ionic equations balance charge in addition to balancing mass (atoms on each side of the equation).
  • The only two elements that are liquids at room temperature and pressure are mercury and bromine. Iodine is a solid at room temperature and pressure.
  • Know the solubility rules. The salts of sodium, potassium, nitrate, and ammonium are soluble in water.
  • Know the common acids. Strong acids are those which dissociate completely in water. Hydrochloric acid (HCl) and nitric acid (HNO3) are examples of strong acids. Acetic acid and carbonic acid are examples of weak bases.
  • When performing gas calculations, be sure to make sure you use temperature in Kelvin.
    It’s common to produce graphs of reaction orders or need to recognize reaction orders from their graphs. The 1/[X] graph of a second order reaction has a positive slope and is a straight line.
  • In a salt bridge, electric charge is conducted by the movement of ions, not electrons.
    Like dissolves like. Nonpolar organics dissolve in nonpolar (covalent) solvents, such as hydrocarbons. Organic molecules with polarity will dissolve in a polar solvent, such as water.
  • The reason alcohol is soluble in water is because it can form hydrogen bonds with water, not because it has a hydroxide group (which it doesn’t have).
    For acid-base problems, remember the larger the Ka, the stronger the acid, while the larger the pKa, the weaker the acid.
  • Only the first bond of a double bond or triple bond counts in a hybridization.
    Double bonds count as one region of electron density. This is useful when predicting shape.
  • Hydrogen bonding is an intermolecular force.
  • A real gas behaves as an ideal gas when it is at a relatively low pressure and high temperature.
  • Hydrocarbons are nonpolar because C and H have similar electronegativity values.
  • Phenolphthalein indicator is pink in basic solution and is colorless in acidic solution.
  • The optimal pH for a buffer = pKa
  • Large K values indicate a chemical reaction is likely to proceed to completion while huge K values indicate the reaction is nowhere near equilibrium.
  • Many transition metal ions form colored solutions.
  • Transition metals lose electrons from the s shell first.
  • Reduction occurs at the cathode.
  • For the laboratory section, remember you clean up a strong acid spill using a carbonate or other weak base, not using a strong base.
  • Again for the lab section, remember you rinse a buret with the solution (not the solvent or some other chemical).
  • It’s possible for the order of reaction to be a fraction.
  • A catalyst increases the rate of a chemical reaction in both forward and backward directions.
  • Breaking bonds in a reactant is an endothermic process.
  • When performing thermochemistry calculations, keep in mind ΔS and ΔH may have different units, so you’ll need to convert to the same units to find ΔG.
  • Fluorine, chlorine, and other halogens always have an oxidation number of -1. Alkali metals such as sodium and potassium have an oxidation of +1.