Introduction to the AP® Chemistry
Multiple Choice Questions (MCQ’s)
A lot of students feel that the MCQ’s are the hardest part of the AP
Chemistry test. And that makes sense, because the multiple choice
questions on the AP exam are not like the kind of easy “free points”
multiple choice questions you’ve probably run into on most exams in
the past.
These MCQ’s require you to combine multiple concepts to answer one
question. In many cases, you’re given information you’ve never seen
before, and you have to think through a series of steps—like solving a
puzzle—in order to get to the right answer.
So what are these MCQ’s actually like? I wrote a collection of AP-style
questions to show you. They might be harder than you’re expecting.
That’s OK. In the video (link and QR code below) we’ll work through
each one, and we’ll talk about strategies and tips for attacking these
difficult questions.
For in-depth explanations, strategies, and tips videos for each question,
check out: https://youtu.be/4XAoHfLi8CI
AP® Chemistry is a trademark owned by the College Board, which is not affiliated with,
and does not endorse, these practice problems or any associated content.
© Bascom Science Incorporated, 2023
Periodic Table of the Elements
Introduction to AP® Chemistry Multiple Choice Questions (MCQ’s)
9 Multiple-Choice Questions
1) The formula for sodium arsenate is Na3AsO4. What is the formula for calcium arsenate?
(A) CaAsO4
(B) Ca2(AsO4)
(C) Ca2(AsO4)3
(D) Ca3(AsO4)2
2) A 64-gram sample of an unknown gas occupies 44.8 liters at STP. Which of the following
could be the identity of the gas?
(A) O2
(B) Ar
(C) SO3
(D) CO
3) An aqueous solution of 1 M potassium nitrate has a boiling point of approximately 101ºC.
Which of the following diagrams most accurately represents the system at a time shortly after it
has reached 101ºC?
4) The following table shows the first five ionization energies (IE) for a neutral element,
measured in kJ/mol.
IE (kJ/mol)
1
2
3
4
5
737.7
1451
7732
10,540
13,630
Which of the following could be the full electron configuration of that element?
(A) 1s22s22p63s23p63d104s2
(B) 1s22s22p63s23p64s2
(C) 1s22s22p63s23p4
(D) 1s22s22p63s23p2
1
5) In a solution of K3PO4, [K+] is 1.5 M. To create this solution, how many moles of K3PO4
would be dissolved in 0.50 L of solution?
(A) 1.5
(B) 0.75
(C) 0.50
(D) 0.25
6) Which of the following is the correct mass spectrum for magnesium?
7)
A2 + B2 → AB2
A chemical reaction is represented by the unbalanced equation above. The diagram beside it
shows relative amounts of starting reactants. Which diagram correctly shows the relative
amounts of substances after the reaction has reached completion?
2
8) A student performs an experiment to determine the molar mass of an unknown monoprotic
acid. A certain mass of acid is dissolved in distilled water and titrated with 1.0 M of NaOH(aq).
All of the following errors result in the calculation of molar mass being too low except for which
one?
(A) The student forgot to convert milliliters to liters, and used milliliters in the molarity
calculations.
(B) The buret was rinsed with distilled water and not 1.0 M NaOH solution.
(C) The student overshot the endpoint by adding too much 1.0 M NaOH solution.
(D) After weighing the solid acid, some is lost before dissolving
9) A 50.0-gram sample of aluminum is at 100°C. It’s placed in 50.0 grams of water at 20°C. The
specific heat of aluminum is 0.89 J/g°C and the specific heat of water is 4.18 J/g°C. The system
is allowed to reach thermal equilibrium. Which of the following is a true statement?
(A) The final temperature of the system is 60°C.
(B) Heat energy was lost by the water and gained by the aluminum.
(C) The aluminum has a higher ∆T value than the water.
(D) The heat gained by the water is approximately four times the heat lost by the aluminum.
3
Introduction to the AP® Chemistry Multiple Choice Questions
Answers and Explanations
1) (D)
A single sodium ion has a charge of +1. Because there are three sodium ions in sodium arsenate
and there is only one arsenate ion, the arsenate must have a charge of -3. A calcium ion has a +2
charge. To balance charges in calcium arsenate, three calcium ions are required to make an
overall +6 charge and two arsenate ions are required to make a -6 charge.
Video Explanation: Ionic Compounds and Formula Writing
2) (A)
1 mole of gas occupies 22.4 liters at STP. Since the sample takes up 44.8 L at STP, there must be
2 moles of gas in the sample. Dividing the mass, 64 g, by the moles gives the molar mass of the
unknown gas, which is 32 g/mol. This molar mass fits O2.
Video Explanation: Gases, STP, and Moles
3) (A)
Potassium nitrate dissociates into K+ and NO3- in solution. Nitrate is a polyatomic ion and does
not dissociate further. The temperature of the solution is at its boiling point, so liquid water
becomes gaseous water, which is depicted as H2O molecules floating as a gas above the
container. Potassium nitrate does not boil at this temperature, and water does not break apart into
H and O when it boils.
Video Explanation: Particle Diagrams of Physical Changes
4) (B)
The large jump in ionization energy between the second and third implies there are two electrons
in the outermost energy level of the element. This suggests that the unknown atom must lose two
electrons to get to stable noble gas configuration. Choice (B) is the only option that will lose two
electrons to get to noble gas configuration. If choice (A) loses two electrons, its configuration
becomes 1s22s22p63s23p63d10 which does have a complete n=3 shell, but is not a noble gas
configuration.
Video Explanation: Electron Configuration and Ionization Energy
5) (D)
1 unit of K3PO4 dissociates into 3 units of K+ and 1 unit of PO43-. There is a 1:3 ratio between
units of K3PO4 and units of K+, so the concentration of K+ in solution will be three times the
starting concentration of K3PO4.
[K+] = 1.5 M, so [K3PO4] = 1.5 M ÷ 3 = 0.5 M.
M = moles/liters, which can be rearranged to moles = M × liters.
!"#$%
L = 0.50, so moles = 0.5 & × 0.5 L = 0.25 moles
Video Explanation: Molarity and Dissociation
1
6) (A)
The atomic mass of magnesium is 24.30. The atomic mass is a weighted average of isotope
masses. Calculating the atomic mass from the mass spectrum in (A) matches the atomic mass of
magnesium:
(24 × 0.80) + (25 × 0.10) + (26 × 0.10) = 24.3
The graph in (A) is additionally the only graph in which 24 is the most abundant by far,
suggesting it will be the only mass spectrum that represents an atom with an atomic mass close
to 24.
Video Explanation: Mass Spectra and Atomic Mass
7) (B)
The balanced chemical equation is A2 + 2B2 → 2AB2. Based on the starting diagram, 1 A2 and 2
B2 will be used up to make 2 AB2. The remaining 3 A2 and 1 B2 will be unused, as there is not
enough B2 for the reaction to run a second time – B2 is the limiting reactant. The final diagram
should have 2 AB2, 3 A2, and 1 B2, which is depicted in (B).
Video Explanation: Stoichiometry and Reaction Diagrams
8) (D)
If some solid acid is lost before dissolving, the acid will require a lower amount of NaOH to
neutralize, so the calculated moles of acid in the sample will also be smaller. When the student
calculates molar mass by dividing the mass of the acid by the moles, the denominator will be
smaller than it should be. This means that the calculated molar mass will be too high.
Video Explanation: Titration Laboratory Experiment
9) (C)
As the two samples reach thermal equilibrium, the aluminum will lose heat energy and the water
will gain heat energy. The amount of heat lost by the aluminum will be equal to that gained by
the water. The two samples will change temperature based on their specific heats. The final
temperature will not be the average of the starting temperatures as suggested in (A). Because
aluminum has a lower specific heat, it will change temperature more than the water, as described
in (C).
Video Explanation: Thermochemistry and Specific Heat
2