AP Chemistry Practice Exam Commentary
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The answer is “D.” Hydrogen Peroxide is commonly used as a disinfectant. It’s the stuff in the
brown bottle in many home medicine cabinets.
The answer is “B.” Kind of a tricky question, bordering almost on trivia. CFC’s
(Chlorofluorocarbons) are commonly associated with refrigerants and ozone depletion.
The answer is “A.” Hydrocarbons especially small ones like Methane and Ethane are key
components to natural gas.
The answer is “E.” Another tricky question. The yellow color makes you think sulfur, but the
fact that it is a solid at room temperature; you should be thinking Ionic (commonly solid) as
opposed to Covalent (commonly gas).
The answer is “A.” π (spoken pi) bonds are any bond existing between two atoms after the first
one. So a single bond only features a σ (spoken sigma) bond or the 1st bond between two
atoms. A double bond features both a σ bond and a π bond. A triple bond features 1 σ bond
and 2 π bonds. So Carbon Monoxide features that triple bond, meaning it has two π bonds.
The answer is “C.” Dipole moment is the strength of the poles in a polar covalent bond. The
greater the Electronegativity difference, the greater the dipole moment.
The answer is “D.” In order to be Trigonal pyramidal you must have a central atom connected to
three other atoms and that central atom must have a lone pair of electrons on it.
The answer is “B.” An excited state is when an atom has electrons that are not in their lowest or
ground state configuration. In “B” the electron in the 2p should be existing in the 2s, but it is
excited.
The answer is “C.” Valence electrons are outermost energy level, not just sublevel.
The answer is “A.” 1st ionization energy is the amount of energy required to pull off an electron.
It increases the “fuller” an atom is and also increases the “smaller” the atom is. In general the
more up and right you are (on the Periodic Table), the greater the 1st Ionization Energy. “A”
represents Helium, that is the most up and right atom.
The answer is “E.” You might be thinking, how am I supposed to know this? Well, just think
about colored solutions you know….do have one in mind? Good. It was likely a Copper
Solution. Elements in the D-Block will commonly have colored solutions. Copper, Cobalt, Iron
and Manganese are all examples you have likely seen.
The answer is “D.” Redox reactions involve changes in oxidation numbers due to electrons
being moved from one substance to another. Synthesis and Decomposition reactions are
common examples.
The answer is “B.” You need a solid produced from two solutions.
The answer is “C.” You must have a complex-ion formed, [Zn(OH)4]2- is about as complex as they
get.
The answer is “C.” A Lewis acid-base involves the acceptance of an electron pair, but because it
isn’t Brønsted-Lowry it can’t involve a proton being accepted. Most complexation reactions are
examples of this. The electron pair on the oxygen is attracted to the Zn2+ ion.
The answer is “E.” Distance between molecules is greatest in a gas.
17. The answer is “C.” The points on this graph are as follows: t1is solid, t2 is melting or equilibrium
between solid and liquid, t3is liquid, t4 is boiling or equilibrium between liquid and gas, and t5is
gas.
18. The answer is “E.” This is a binary ionic compound featuring no polyatomic ions. Cation
maintains elemental name, anion ends in –ide. No prefixes. (Those are only for covalent)
19. The answer is “D.” You might be panicking….I need a calculator for this. No you don’t. They
pick simple numbers that look scary. To solve for moles, convert your 250 mL to L and multiple
by molarity. 0.25 L x 0.4 M = 0.1 moles. They use numbers like this for a reason. 0.1 x 119 =
11.9.
20. The answer is “B.” If you weren’t panicking before about a calculator, now you definitely are.
You don’t need to. They picked super easy numbers. This is a Ka/weak acid problem.
In general, the pH will be about half of the exponent value. -6 was the exponent, pH is about 3.
If the exponent was -4, the pH would have been about 2.
21. The answer is “E.” The key to this question is understanding Le Châtelier’s principle with respect
to pressure changes. Increasing pressure shifts towards the side with fewer moles of gas.
Remember solids are not included in equilibrium.
22. The answer is “D.” We are approximating energies. We know that 1 mole of HI decomposing
would release 26 kJ, we need 500 kJ, that’s about 20x the energy of 1 mole (slightly less, but
we’re approximating). So I need 20 moles of HI, each mole is about 130 g, so I need about 2600
g, nearest answer is “D.”
23. The answer is “C.” Tricky question for sure. ΔS is the measure of disorder. Solids dissolving
general lead to less order, but in this case, they are saying that it is becoming more ordered.
You have to think about the process of dissociation. When it breaks apart, the ions are now
being dispersed throughout the solution. The water will then orient itself around each ions
(hydration), it turns out that by adding some salts, the solution will actually become more
organized. This actually explains why some salts become less soluble with increasing
temperature.
24. The answer is “C.” Easy balancing, just don’t forget about the Oxygen in the CH3OCH3 (this is an
ether, in case you were wondering).
25. The answer is “C.” Easy question, if you avoid getting too fixated on the words. – ΔS is
becoming more ordered. Formation of a solid is definitely becoming more ordered.
26. The answer is “A.” This is an example of a lab question you may see. This is also an example of
how distractors (incorrect answers) can be entirely irrelevant. We know a certain amount of gas
is lost, where did it go? In dissolves into water, we know CO2 is soluble in water, hence Soda.
27. The answer is “D.” Not a terribly scary math question. It is a 2:1 ratio of Cu:Cu2O. If we had
0.40 moles of Cu2O, then we must have had 0.80 moles of Cu. Convert to grams, MMcopper is like
63 g/mole. 51 grams is closest.
28. The answer is “E.” They don’t do much organic, but it does show up occasionally. An Ether is an
organic molecule with an Oxygen in the carbon chain. For reference, “A” is a Ketone, “B” is a
Carboxylic Acid, “C” is an Alcohol, “D” is an Aldehyde and as stated before “E” is an Ether. This is
probably the extent of Organic you will need.
29. The answer is “B.” The initial total pressure was 1.5 atm, it’s now 3.0 atm. Each partial pressure
will double.
30. The answer is “D.” This is a tricky question, because A, B and C are all true statements. A and B
would have the opposite effect based off of the data provided, so those can’t be the reason. C
sounds like such a good answer, but it has everything to do with electrons, not mass. It’s
essentially a London Dispersion Forces idea.
31. The answer is “A.” When we talk about gasses behaving ideally, we want them at high
temperatures and low pressures. Under these conditions, gas particles won’t interact with one
another very often. Aspects of polarity and size (molar mass) will make gasses behave less
ideally. So in order to deviate from ideal conditions, we want low temperatures, high pressures,
polar molecules and large molar masses. For comparison, “D” would be the most ideal
behavior.
32. The answer is “C.” This is a simple half-life question. The original sample is 10 g, so after one
half-life, it’ll be at 5 g, after 2 half-lives it’ll be at 2.5 g and finally after 3 half-lives, it’ll be at 1.25
g as the problem depicts. It took 195 days to go 3 half-lives, so 195 days divided by 3 gives us 65
days.
33. The answer is “B.” Devious little question. Instinct would be to likely say “A.” In order to
produce high amounts of CO2, you need a high percentage of C. This is essentially a percent
composition question. The higher the % C in the compound, the higher the amount of CO2 that
is produced. For reference, the amounts are 27.5 g, 13.75 g, 31.43 g, 29.33 g and 25.14 g
respectively.
34. The answer is “B.” Remember, Hydrogen bonding is between H and either F, O or N. Nothing
else. Only “B” features that kind of bonding.
35. The answer is “B.” It’s asking for *OH-], so we relate, pH and pOH. pOH is 2.5. [OH-] =
.
Do you need the exact value without a calculator….of course not. We are approximating here.
This is less than 10-2, so it is likely close to 10-3.
36. The answer is “C.” Temperature affects the value of Keq, everything else either has no effect or
simply shifts equilibrium, but does not impact the constant.
37. The answer is “E.” The cathode is the site of reduction. We use E° to determine what is going to
happen. The most positive E° is that of Fe3+ so we know that is the substance that will be
reduced. Additionally as Fe3+ is being reduced, Fe2+ will be produced, so both will be present.
38. The answer is “D.” If we flip the Zn2+equation, we get a +0.76 V for the oxidation of Zn, we add
that to the reduction of Fe3+ (0.77 V) and we get 1.53 V.
39. The answer is “C.” In problems related to Ionization Energies, the key is to look for a big jump in
energies. This substance seems reasonably will to give up 4 electrons, but not 5. That means
this substance likely has 4 valence electrons, which all Carbon group elements possess.
40. The answer is “E.” This is a balancing nuclear equations problem. The substance does not
change mass, but we see a change from Ca to K, so a proton is converted to a neutron. If we are
depicting this we get:
It must be a β+. It has no mass, but a positive
charge.
41. The answer is “C.” This is an ideal gas law question. 40 g of Ar is essentially 1 mole. You may
have remembered that 1 mole of gas occupies 22.4 L at STP, but because we have 2 atm, it must
be at 2 x Standard Temperature (273 K) which gives you approximately 550 K. You could have
also done this by saying 2 x 22.4 = 1 x 0.0821 x T. This gives you 44.8/0.0821. This may seem
like a tough problem to do in your head, but dividing by 0.0821 is like multiplying by 12.
42. The answer is “B.” This is ΔTb question. We want the highest boiling point, so we need the
greatest molality x van hoff’t factor. A and B, both have van hoff’t factors of 3, where C and D
both have van hoff’t factors of 2 and E has a van hoff’t of 1 (It’s covalent, thereby a nonelectrolyte).
43. The answer is “A.” This is a ΔG = ΔH – TΔS relationship. We are saying that ΔG becomes
positive about 400 K. So we know at 400 K, ΔG = 0. If ΔH is -20 kJ/mole, that means that TΔS is
-20 kJ/mole at 400 K. -20 kJ/400 K, gives you -0.05 kJ/mole·K or -50 J/mole·K.
44. The answer is “C.” To determine Molarity, you need to know Volume and the total mass
(assuming you know mass of solute). Temperature is irrelevant.
45. The answer is “D.” This is a simple-ish redox balancing. H+’s or waters needed.
(Au3+ + 3 e-  Au) x 2
+ (2 I-  I2 + 2 e-) x 3
2 Au3+ + 6 I-  2 Au + 3 I2
46. The answer is “C.” Gas solubility is best thought of based off of prior experiences. When you
shake soda, does more Carbon Dioxide go into solution? Of course not. By raising temperature,
the gas is more likely to escape the solution. Gas solubility is dependent largely based on the
pressure being exerted above the gas. Add more gas, more gets forced into the solution.
47. The answer is “E.” The reaction is 1st order with respect to Z. The straight line plot versus Time
will be the ln [Z].
48. The answer is “D.” This is a limiting reactant question. From the CS2 it is a 1:3 ratio in terms of
products. So from 0.60 moles, you could produce 1.8 moles of product. From the O2 it is a 3:3
ratio in terms of products. So from 1.5 moles, you could produce 1.5 moles of product.
49. The answer is “A.” The ice cubes were not weighed prior to addition to the cup, the only way to
determine their mass was to measure it at the end.
50. The answer is “C.” If the ice cubes had not been dried before addition, the mass measured at
the end would not have just been ice, but also some water. This would give you less ice than
you thought.
51. The answer is “B.” Bond order is the number of bonds between atoms. A decimal value
indicates resonance. O3 is the only molecule of the set that demonstrates that.
52. The answer is “E.” Alkali metals react violently with water.
53. The answer is “B.” Kind of a strange way of wording this, but essentially this is a question of
your understanding of a heating curve. Temperature remains constant during the phase
change.
54. The answer is “D.” This is a coulombetry question. Pretty tricky for sure. In 1 hour 243 g of Mg
is produced from Mg2+ ions. 243 g of Mg is 10 moles and each mole required 2 moles of
electrons, so in that 1 hour, 20 moles of electrons were supplied. So if we supply 20 moles of
electrons to Al3+, we’ll produce 6.67 moles of Al (3 moles of e- per mole of Al). 6.67 moles of Al
weighs about 180 g.
55. The answer is “D.” This is just a definition question. Brønsted-Lowry bases can accept protons.
F- and OH- will do this in this reaction.
56. The answer is “C.” Percent composition question. A little tricky without a calculator,
approximately as best as possible.
57. The answer is “E.” If a substance is at its melting point, it is in equilibrium. From a
thermodynamics standpoint, ΔG is zero. If ΔG = ΔH-TΔS, then 0 = ΔH-TΔS, so ΔH =TΔS.
58. The answer is “D.” Both reactions will speed up, but will result in a shift to the right due to the
forward reaction being endothermic.
59. The answer is “B.” The metal X must have a 3+ charge, because each chloride ion is 1-. If we
combine that with a sulfide ion (2-) is must be X2S3.
60. The answer is “C.” We are adding base to an acid that has phenolphthalein in it. At the end
point, it will be slightly in excess base and with phenolphthalein it is pink in basic environments.
61. The answer is “D.” We started with 12.60 mL and ended with 35.80 mL, the difference is 23.20
mL.
62. The answer is “B.” This reaction will occur spontaneously, but in order to get the reaction
started, a large amount of energy must be supplied.
63. The answer is “B.” This is an ideal gas law question. We have 0.1 moles of S8 reacting fully to
produce H2S. It is a 1:8 mole ratio, so 0.8 moles of H2S will be produced. Use pV=nRT. Once
again, under STP, it’s about 22.4 L/mole. 0.8 x 22.4 is about 20 L.
64. The answer is “D.” H is generally +1 and O is generally -2. The sum of the oxidation number in
neutral compounds is zero, so using that idea, it will be +1 to +7.
65. The answer is “E.” You can only create solutions whose concentrations would be between 0.25
M and 0.15 M, in order to make anything less you would need to add water. In order to make
anything greater you would need to add more solute.
66. The answer is “D.” Very difficult question without a calculator. We know the [OH-] at
equilibrium is related to pH. pH = 9, so pOH = 5. This means [OH-] = 1 x 10-5. Because this is
dibasic, it means that the [M2+] is half of [OH-], in this case 5 x 10-6. If we plug this into the ksp it’ll
be (1 x 10-5)2(5 x 10-6) = 5 x 10-6.
67. The answer is “E.” In order to accurately prepare a solution you need a volumetric flask. This
will allow you to measure solution volume as opposed to just solvent volume.
68. The answer is “C.” Radius decreases as you go right to left across a row and increases as you go
down a column. Cations are always smaller than their neutral form (you’re taking away e-‘s).
Anion are always larger than their neutral form (you’re adding e-‘s).
69. The answer is “A.” Surface area speeds up chemical reactions. Sawdust is wood with greater
surface area.
70. The answer is “E.” Chemical similarity is related to valence electrons. Elements in the same
column of the periodic table are generally very similar.
71. The answer is “C.” Endothermic processes are those that require energy. Breaking bonds (in
these cases hydrogen bonds) from both the methanol and water standpoint are occurring. The
intermolecular attractions are exothermic (newly formed hydrogen bonds between water and
methanol).
72. The answer is “D.” Average molecular speed is related to two factors, temperature and molar
mass. All of these substances are at 298 K, so we are looking at masses. Mass is inversely
related to speed. So fastest will have the lowest molar mass.
73. The answer is “C.” Hybridization is related to bonding patterns in a molecule.
This is what propyne will look like. All first bonds (σ) between atoms and lone pairs of electrons
are deemed to be hybridized (essentially meaning that they have equal energy). So if we are
looking at the different carbon atoms in this molecule, the left most carbon has 2 hybridized
bonds, the middle carbon has 2 hybridized bonds and the right most carbon has 4 hybridized
bonds. We name the hybrid orbitals by looking at what was hybridized and how many orbitals
were used. If it is the blending of an s electron orbital and a p electron orbital, you get 2 sp
orbitals. The rest follow the system depicted below. Essentially you are just counting up to 6.
# of Hybridized Orbitals
2
3
4
5
6
Hybridization
sp
sp2
sp3
sp3d
sp3d2
74. The answer is “B.” Kind of sneaky question here. If you have 0.050 m XY2 it’ll dissociate 40%. So
that means that 40% of 0.050 m will break apart into 3 ions. So 0.020 m ionizes and 0.030 m
does not. The 0.020 m will produce 0.060 m of ions. That plus the 0.030 m that did not ionize
leaves you with 0.090 m.
75. The answer is “C.” First, it needs to have covalent bonds. So we can eliminate A and B. C, D and
E all have covalent bonds, but in D and E’s cases it is intermolecular forces (not covalent bonds)
being broken. Graphite is a covalent network solid, this means that it is essentially covalent
bonded in all directions. Diamond and glass are also examples of this. So as the phase change
happens, you are actually breaking bonds, not just intermolecular forces. This explains the very
high melting point of things like glass, diamond and graphite.