 MAST Master-Tutor, Dora L. has come up with some tips for the AP Chemistry exam. She is an experienced teacher with 28+ years under her belt, of which 14 years were spent teaching AP Chemistry. She was also a 2016 AP Chemistry Reader, so she knows the in's and out's of the AP Chemistry Exam. We hope these tips will help your understanding and preparation for the exam!

AP Chemistry Exam Tips

Posted by: Dora L.
Date: May 6, 2018

1. Introductory Concepts in the AP Chemistry Exam

• Calculate average atomic mass based on mass spectrum with relative % abundance and mass data of isotopes

2. Stoichiometry in the AP Chemistry Exam

• Use Limiting Reactant to determine mass of product formed and calculate % yield; interpret particle drawings

3. Reactions in the AP Chemistry Exam

• a) Use Gravimetric Analysis technique to determine mass % in a sample
• b) Prepare diluted solution from a stock solution by using appropriate lab apparatus based on required significant digits
• c) Justify a reaction being Acid/Base, Precipitation, or Redox
• d) Write balanced net ionic equations for various types of reactions

4. Gas Laws in the AP Chemistry Exam

• a) Know the inverse mathematical relationship of pressure and volume in Boyle’s Law
• b) Use the direct proportional relationship between pressure and moles in solving gas stoichiometry problems
• c) Calculate partial pressure of a gas from mole fraction and total pressure in a mixture
• d) When gas is collected over water, vapor pressure of water must be accounted for when determining pressure of a dry gas
• e) Concepts of Kinetic Molecular Theory as related to various gas laws
• f) Use Ideal Gas Law PV = nRT to solve problems
• g) Velocity of a gas is directly proportional to temperature but inversely proportional to its molar mass
• h) Use Graham’s law of Effusion to account for which gas moves faster
• i) Optimal Ideal Gas behavior is at low pressure and high temperature
• j) Van der Waal’s equation accounts for less volume of container available for collision of larger gas
molecules and lower observed pressure due to intermolecular force of attraction

5. Thermochemistry in the AP Chemistry Exam

• a) Use Q = m s (ΔT) to calculate heat in a calorimeter
• b) ΔH = - Q / moles (of limiting reactant)
• c) Use Hess’s Law to arrive at ΔH of targeted equation
• d) Calculate heat energy for various segments of heating curve
• e) Calculate ΔH from enthalpies of formations of products and reactants
• f) Understand ΔH in kJ/mole of rxn is related to moles in a balanced equation

6. Atomic Structure in the AP Chemistry Exam

• a) Calculate E = hv
• b) Calculate energy released when electron transits from a higher energy to a lower energy level and determine the frequency of color emitted
• c) Write electron configurations for atoms and ions
• d) Account for periodic trends of atomic radius, ionization energy, electron affinity, and electronegativity using Coulomb’s Law (effective nuclear charge and electron shielding effect)
• e) Interpret PES diagrams for electrons in specific orbital and energy levels
• f) Use Beer’s Law to determine the concentration of a colored species based on absorbance values in a standard calibration curve
• g) Understand the atomic principles behind Infrared and Utraviolet/Visible spectrum
• h) Interpret the potential energy diagram of bond energy and bond length
• i) Describe the energy process in forming an ionic compound from its elements
• j) Use Coulomb’s Law to account for lattice energy differences in ionic solids
• k) Calculate ΔH from the difference of bond energy absorbed in breaking bonds of reactants and bond
energy released in forming bonds in products
• l) Draw Lewis structures and resonance structures for covalent compounds
• m) Use formal charge to depict the most preferred Lewis structure
• n) Use VSEPR to predict molecular geometry and bond angles
• o) Name orbital hybridization sp, sp2, sp3 of various molecules
• p) Recognize sigma and pi bonds

7. Intermolecular Forces & Solution Formation in the AP Chemistry Exam

• a) Name the IMF’s existing in molecules – LDF, Dipole-dipole interactions, Hydrogen Bonding, Dipole induced dipole, Ion-dipole attractions
• b) Use relative strengths of IMF to account for relative boiling points, or why a substance is a solid, liquid, or gas
• c) Recognize hydrogen bonding from molecular structures
• d) Know the properties and structures of Ionic Bonding, Metallic Bonding, Network Covalent Bonding
• e) Recognize the difference between Interstitial alloy and Substitutional alloy and their functions
• f) Recognize the n-type and p-type semiconductors
• g) Use the concept of enthalpy of solution to account for solubility of polar or non-polar solutes in polar or non-polar solvents

8. Kinetics in the AP Chemistry Exam

• a) Know the 4 factors affecting rate of reaction, and the interpretation of their kinetic energy distribution diagrams
• b) Explain the shape of the curve in a concentration vs time graph
• c) Use mole relationship to relate rate of appearance of product to rate of disappearance of reactant
• d) Use experimental data to derive rate law
• e) Use Integrated rate law to find concentration of reactant at a specific time, know the plot to give a straight line, the relationship of rate constant k to the slope of the line, and derive the unit of k
• f) Determine half-life from a 1st order graph or data, or use half-life to calculate k
• g) Understand that the Collision model depends on proper orientation of molecules with sufficient energy in collision
• h) The magnitude of rate constant depends on temperature and is inversely proportional to the size of activation energy
• i) Write rate law based on the rate determining step in a proposed reaction mechanism
• j) Differentiate between catalyst and intermediate in elementary steps
• k) Draw potential energy diagrams based on reaction mechanism with or without a catalyst
• l) Explain how homogenous and heterogeneous catalyst increases reaction rates
• m) Be familiar with the Crystal Violet Lab, pseudo rate constant, serial dilutions, standard calibration curve

9. Chemical Equilibrium in the AP Chemistry Exam

• a) Be able to write equilibrium expression for Kc and Kp
• b) Set up ICE table to solve equilibrium problems
• c) Use Q vs K to predict direction of reaction, and whether concentration of species would increase or decrease
• d) Use Le Chatelier’s Principle to account for equilibrium shift
• e) Recognize that only temperature increase or decrease in endothermic and exothermic reactions changes the value of K

10. Acids & Bases in the AP Chemistry Exam

• a) Name Bronsted-Lowry Acid-Base conjugate pairs and compare their relative strengths based on magnitude of K
• b) Draw Lewis diagrams for transfer of proton in acid-base conjugate pairs
• c) Know that ionization of water is endothermic.  The higher the temperature, the greater is magnitude of Kw, the smaller is magnitude of pKw, and the lower is the pH
• d) Ionization of a weak acid increases by adding water
• e) For equal pH of a strong acid and a weak acid, the strong acid has lower molarity
• f) Use Ka or Kb to find pH of a weak acid or weak base from its ionization
• g) Account for the decreasing trend of successive Ka values in a polyprotic weak acid
• h) Predict the acid-base properties of salt solutions
• i) Account for the strengths of binary acids using bond energy, and strengths of oxyacids using electronegativity

11. Buffer & Titration Curves in the AP Chemistry Exam

• a) Select appropriate components to prepare a buffer solution based on pH and pKa
• b) Write net-ionic equations to account for the resistance to pH change of a buffer when small amounts of strong acid or strong base is added
• c) Use Henderson Hasselbalch equation to calculate pH of a buffer
• d) Compare and rationalize buffering capacities
• e) Calculate pH values of 3 titration curve (strong acid/strong base, weak acid/strong base, weak base/strong acid); know their characteristic shapes, identify buffer region, draw particle diagrams, describe relative concentration of weak acid and conjugate base, and determine pKa values
• f) Choose proper indicator for a titration based on equivalence pH

12. Ksp in the AP Chemistry Exam

• a) Write Ksp expressions
• b) Calculate molar solubility and concentration of ions from Ksp, or vice versa
• c) Compare relative solubilities using Ksp for similar or different dissociation stoichiometry
• d) Solve molar solubility with common ion effect and pH effect
• e) Predict precipitation by comparing Q vs Ksp
• f) Separate a mixture of metal ions in aqueous solution by selective precipitation using Ksp calculations

13. Thermodynamic Favorability in the AP Chemistry Exam

• a) Use the two driving forces, enthalpy and entropy, to predict the thermodynamic favorability of a reaction
• b) Explain the effect of temperature on spontaneity
• c) Relate free energy to magnitude of equilibrium constant

14. Electrochemistry in the AP Chemistry Exam

• a) Define oxidation number of an element in a chemical formula
• b) Balance redox reactions using half-reaction method
• c) Understand the operation of a Galvanic cell, reduction at cathode and oxidation at anode, function of salt bridge, direction of electron flow, and calculate cell potential
• d) Predict increase or decrease of cell potential with change of concentrations of reactants or products, and explain using Le Chatelier’s principle
• e) Determine and cell voltage for half-reactions for electrolysis
• f) Calculate mass of metal deposited in electroplating from current or time
• g) Relate cell potential to free energy to equilibrium constant

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