2002 AP Chemistry Practice Exam Commentary
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The answer is “A.” To determine the number of unpaired electrons, we must think about the
orbital diagrams of the last sublevel for each (every other orbital will be paired up). Sulfur has
an outermost electron configuration of 3p4. The first orbital of the sublevel will be filled; the
other two will only have one electron in each. For reference, the number of unpaired electrons
for the atoms would be 2, 0, 1, 3 and 1. (63% correct)
The answer is “C.” We are once again looking at electron configuration here. We want only 1
electron present in its highest energy sublevel (s, p, d or f). Upon analysis we see that Gallium
only has one electron in its 4p sublevel. For reference, the number of electrons in the highest
occupied energy sublevel for the atoms would be 4, 2, 1, 3 and 5. (70% correct)
The answer is “D.” This is a covalent bonding problem. Draw out the structures that you are not
sure about, but try not to spend too much time on a problem like this. You’ve seen CO2, H2O
and CH4 many times, so hopefully you didn’t draw them out. An important skill is to think about
things that are similar. Phosphorus and Nitrogen are in the same column, so they behave very
similar in terms of bonding. You’ve seen NH3 many times as well, so PH3 looks just like it. C2H4
features 1 double bond between the two carbons in the molecule. CO2 is the only other
molecule with double bonds, but it features two. (74% correct)
The answer is “B.” Dipole moment means largest dipole. Dipoles are created due to
electronegativity differential. Oxygen and Hydrogen have the largest difference. This also
justifies why hydrogen bonding is just a really strong form of a dipole. (54% correct)
The answer is “E.” In order to have a trigonal pyramidal geometry, you must have three things
connected to a central atom with one lone pair. For reference this is an sp3 hybridized molecule.
PH3 will be that. (75% correct)
The answer is “C.” This is one of those you either remember using it in the lab or not.
Qualitative/descriptive chemistry is memorization. Permanganate is purple, think pomegranate.
Maybe it’ll click. They use that one a lot. (55% correct)
The answer is “D.” We need a soluble compound, so that eliminates “A” and “B.” We have
already established that “C” is purple, so that leaves us with KCl and FeCl3. KCl is very similar to
NaCl (a white solid) and FeCl3 features a D-block cation. D-block cations are very typically
colored. (61% correct)
The answer is “D.” Molecular speed is determined by molar mass and temperature. Given a
constant temperature we are looking for the compound/element that has the molar mass
closest to N2 (28 g/mole). CO has the same molar mass. (41% correct)
The answer is “B.” Gas density is directly proportional to molar mass. Highest molar mass has
the highest density. The order is as follows: Ne < CO < NO < O2 < Xe (71% correct)
The answer is “A.” Effusion (and diffusion) are related to velocity. The greater the velocity, the
greater rate with which it can escape. As was just stated, molar mass is the key to this. Low
molar mass, high velocity. Ne has the lowest molar mass, thus highest effusion. (59% correct)
The answer is “D.” A precipitation reaction involves two ions in solution interacting to produce
an insoluble compound. That is what we see in “D.” (82% correct)
12. The answer is “E.” A coordination complex is another name of a complex ion. The only one that
is there is the PtCl62-. In general complex ions, look….well, complex. (30% correct)
13. The answer is “C.” This problem requires you to think about two different things, redox and
oxidation numbers. We can eliminate “D” and “E” as they are not redox. In “A” and “B” there
are clearly two reactants that are being either oxidized or reduced. In “C” Br2 is both being
oxidized to BrO3- and being reduced to Br-. Tricky question, but you should be able to answer by
elimination at the very least. (67% correct)
14. The answer is “B.” I don’t love this as an answer. Combustion reactions are best thought of as a
hydrocarbon interacting with O2 to produce CO2 and H2O. It can be thought of as redox with O2
as a reactant producing an oxide product. (74% correct)
15. The answer is “B.” Horizontals are phase changes. Freezing occurs at the lower temperature of
the two. t1 is still all solid and below its melting/freezing point, so t2 is the right answer. (56%
correct)
16. The answer is “A.” We are in the second horizontal of the phase diagram, meaning boiling.
Between t4 and t5 more water is boiling, meaning the substance is leaving liquid phase to
become a gas. (58% correct)
17. The answer is “A.” Simply determine the number of electrons each species has. Anions
(negative ions) have as many additional electrons from neutral as its charge. Cations (positive
ions) have as many fewer electrons from neutral as its charge. (70% correct)
18. The answer is “D.” In this phase diagram, all three physical states are shown. The left most
region is solid, the middle area is liquid and the lower right is gas. (This is the case for all phase
diagrams such as this) If we work our way across at 0.5 atm from 10°C to 100°C we will go from
solid to gas (subliming) at about 20°C. (69% correct)
19. The answer is “E.” We must first determine the oxidation number of S in H2SO4, which is +6. We
then need to calculate it for the rest. For reference, the oxidation number of sulfur in each is +4,
+2 each, -2, 0 and +6. (72% correct)
20. The answer is “E.” Pressure is proportional to moles. If the total pressure is 800 mm Hg, the
pressure of each gas is related to their percentage or mole fraction. SO2 is 0.25 moles and there
are 1.25 total moles, so it is 1/5th of the total moles, so it is 1/5th the total pressure. 1/5th of 800
mm Hg is 160 mm Hg. (67% correct)
21. The answer is “B.” H2 is most commonly produced when acids react with metals. When HCl
reacts with NH3, this is a strong acid/weak base interaction, producing water and conjugate acid.
When HCl reacts with NaHCO3, a gas will be produced, but that gas will be CO2, as is the case
with all acid/carbonate or bicarbonate reactions. (48% correct)
22. The answer is “C.” When NH3 accepts a proton, it becomes NH4+. NH3 is acting as a base, which
means NH4+ is its conjugate acid. (57% correct)
23. The answer is “D.” We must have the same mass and charge on each side. On the left, we have
a total mass of 236 and a total charge of 92. We have 141 from the Cs, 3 from the 3 neutrons,
which means the mass must be (236-144=92) and a charge of 55, which means (92-55=37).
(37% correct)
24. The answer is “C.” The simplest formula is the one with the lowest ratio of moles. The lowest
value any atom can have is one, so we take the lowest value and divide all of them by that value,
in this case 0.55. 0.55/0.55=1, 1.1/0.55=2, 1.65/0.55=3. We end up with K2TeO3. (82% correct)
25. The answer is “A.” This is heat of reaction question. Sum of products-Sum of reactants. Keep in
mind that you have three moles of reactant. (83-(3x230)) = -607 kJ. (66% correct)
26. The answer is “B.” We need to determine how many moles we need in our solution and then
convert to grams. If were making one liter of 0.1 M, we’d need 0.1 moles, but we are making ¼
of a liter, so we’ll need ¼ of 0.1 moles, which is 1/40th of a mole. Molar mass is 250 g/mole, so
1/40th of 250 g is about 6.2 g. (56% correct)
27. The answer is “A.” We need to look only at the slow step, given the slow step is the first step.
The reactants of the slow step become part of the rate law, NO appears twice, which means that
it is second order. (45% correct)
28. The answer is “E.” The degree of being ionic is largely based on electronegativity difference.
The more left you are the more metallic, the more right you are the more electronegative you
are. Calcium and Chloride fit the bill the best. (68% correct)
29. The answer is “C.” Diamond is an example of a covalent network solid. Essentially a diamond is
just one big molecule, featuring only C’s connected to other C’s. We see the same kind of
bonding demonstrated in Graphite and Glass. (51% correct)
30. The answer is “C.” In order to find [OH-] we need pOH. pH + pOH = 14, so pOH = 6. To find
[OH-] it is 10^-6. (72% correct)
31. The answer is “A.” Moles are proportional to volume, the mole ratio of CO2:O2, is 1:3, and we
have 4 L of CO2, which means we will need 12 L. (56% correct)
32. The answer is “B.” Gasses at room temperature of nearly always (can’t think of an exception….)
covalent. Covalent is nonmetal bonding. Nitrogen and oxygen are both non-metals. (69%
correct)
33. The answer is “D.” When choosing an indicator, we want it to change color when your titration
plot is in its “vertical” component. This is where the equivalence point is and we want our
endpoint (color change) to be as close to that as possible. (70% correct)
34. The answer is “A.” The optimum buffer region is when the weak acid is equal to its conjugate
base. This occurs in the most horizontal portion of the titration curve prior to equivalence, this
is showing resistance to pH change. It always will be halfway to the equivalence point. (34%
correct)
35. The answer is “A.” Adding nonvolatile solute to solvent will always raise its boiling point and
lower its freezing point. The degree of its effect is based on the individual substance added and
its concentration. (53% correct)
36. The answer is “B.” A lot to think about and process in this question. What we can tell is that a
white metal chloride is produced and then a yellow metal iodide was produced. Hopefully you
remembered the color of AgCl and PbCl2, if you didn’t you could have at least eliminated any of
the ones with Barium as it would not precipitate, giving you a 50/50 shot. (28% correct)
37. The answer is “A.” We want to increase the ratio of Carbonate to Bicarbonate, so we want to
shift the equilibrium to the right. The forward reaction is exothermic, by reducing the
temperature, it will slow the reverse reaction and cause a shift it to the right. (45% correct)
38. The answer is “D.” Conductivity is based on ions in the solution. Sodium sulfate will break into
three ions, which Sodium Chloride will break into two ions. (61% correct)
39. The answer is “B.” We are looking for the substance that will decrease the most in terms of
solubility from 90° to 30°, we will be able to recover all of the solute that has fallen out of the
solution by filtering it out. KNO3 has the greatest drop. (73% correct)
40. The answer is “D.” This is a very difficult question without a reaction or a calculator. The ratio
of moles of HCl to H2 is 2:1. From 100 mL of 0.4 M HCl we can determine that 0.04 moles HCl
used, which means that 0.02 moles H2 are produced. That’s 1/50th of a mole. At STP 1 mole of
gas is 22.4 L. 1/50th of 22.4 L is just less than ½ L. (29% correct)
41. The answer is “C.” Quite a few things to think about. First, the reaction happens, so it is
spontaneous, meaning it is a negative ΔG. Second, the reaction gets colder, so it is endothermic,
meaning a positive ΔH. Lastly, gasses are produced from solids, so this is increasing entropy,
meaning a positive ΔH. (43% correct)
42. The answer is “B.” When we flip a system at equilibrium, the K value will be the reciprocal. So,
our answer is
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2 𝑥 105
A little difficult to do without a calculator, but the answer is 5 x 10-6. (24%
correct)
The answer is “D.” We have the average atomic mass and its closer to Cu-63 than Cu-65. By
approximation it is about 70% of the way between 63 and 65. (49% correct)
The answer is “E.” Atomic radius decreases across a period due to increased nuclear charge,
more effectively attracting valence electrons. (70% correct)
The answer is “A.” If we assume that we have 100 g, then 46 g of Ethanol and 54 g of Water.
With molar mass we have 1 mole of Ethanol and 3 moles of Water. Mole fraction is moles of
Ethanol over total moles. ¼ is 0.25. (44% correct)
The answer is “B.” Effective nuclear charge is based off of two factors, distance and quantity.
The electrons are further away in Na than Ne, but Na has only a slightly greater quantity of
protons. This explains why Na is very likely to lose that single electron in its valence level. (62%
correct)
The answer is “C.” The only way reaction order can be determined is experimentally. It can be
related to the equation, but not required. And in super rare scenarios it can be 0.5 or 1.5. (39%
correct)
The answer is “B.” Like dissolves like. The more polar the substance is the more it will dissolve.
Carbon Tetrachloride is non-polar, so very little salt will dissolve in it. (48% correct)
The answer is “D.” Full on redox balancing. Probably not worth the time required to answer it
fully. Time is of the essence. Quick analysis, we will need 2 Cr3+, 1 Cr2O72-, so the only thing on
the left that will balance charge is the H+, -2 on one side + ___H+ ions, equals +6. It must be 8.
(31% correct)
The answer is “C.” Tricky because you may have thought A. It’s just something that you don’t
do as it can damage the equipment. For C, if you’re performing a titration, you’re going to be
adding water to dissolve the acid and we already measured its mass. (16% correct)
The answer is “B.” Copper is being oxidized, so it is the reducing agent. Nitrogen is +5 in NO3and +2 in NO. Hydrogen is existing as +1 on each side. (49% correct)
52. The answer is “B.” The products of the combustion are CO2 and H2O. Write out the equation
and balance. C3H8 + 5 O2  3 CO2 + 4 H2O. (71% correct)
53. The answer is “D.” What is occurring here is that as additional the additional electron pairs are
“squeezing” the bonds closer together, thus reducing the bond angles. Not a huge impact, but it
will bring the 109 degree angle of the tetrahedron to about 107 for the trigonal pyramidal and
104 for the bent. (62% correct)
54. The answer is “D.” Kind of a strange question, but when you think about the energy diagram it
makes sense. Activation energy is calculated by looking at energy of reactants and energy at the
transition state. The transition state will be at the same point regardless of direction, so if it is
the same, then the energy of products must be equal to the energy of the reactant. So ΔH = 0.
(43% correct)
55. The answer is “A.” We can see that it is dropping by half every 3 days. 0 to 3 days, goes from
100 to 50. 3 to 6 days, goes from 50 to 25. The half life is constant, that means it is a first order
decay. If it was not constant it could have been second order. (55% correct)
56. The answer is “A.” The noble gasses only demonstrate dispersion forces. As the number of
electrons increase, so do intermolecular forces, so does boiling point. (62% correct)
57. The answer is “D.” We are doubling both reactants. When we double a first order reaction, it
will double the rate. When we double a second order reaction, it will quadruple the rate. When
we do both it increases by 8x. (52% correct)
58. The answer is “A.” This is a stoichiometry problem. We have 0.25 moles of N2H4 and 1 mole of
N2O4. From the equation, we can see that 0.50 moles of H2O can be produced. Using molar
mass, we take 0.50 moles x 18 g/mole we get 9 grams. (47% correct)
59. The answer is “B.” We just need to analyze each statement. Non-metals are poor conducts.
Chlorine, bromine and iodine are not colorless. Chlorine is not odorless. Bromine and Iodine
are not gasses, but they are all diatomic. (40% correct)
60. The answer is “A.” This is a solution stoichiometry question. Convert our solution to moles and
use the ratio above. 20 mL (0.02 L) of 0.2 M is 0.004 moles. It is a 4:3 ratio, so 0.004 moles will
produce 0.003 moles of ClO2-.
61. The answer is “C.” To lower the pH by 1 point, we must reduce the concentration by a factor of
10. 100 mL of pH 13, must be diluted 10x. (22% correct)
62. The answer is “B.” A structural isomer means, the same chemical formula, but a different
structure. We have to move the Br off of one of the outer Carbons. That’s B. (28% correct)
63. The answer is “B.” A buffer is prepared by taking a weak acid and conjugate base. HCl and HBr
are both strong acids, so they will not form a buffer. (25% correct)
64. The answer is “E.” Brutal question. Essentially this is a system of multiple equilibrium. This is
remarkably unlikely to be asked on the exam, but the beginning explanation is still valuable. The
two equilibrium will look like this:
First Equilibrium: H2C6H6O6 ⇋ H+ + HC6H6O6Second Equilibrium: HC6H6O6- ⇋ H+ + C6H6O62So the first we analyze the K values. First equilibrium happens to a greater extent than the
second, so the products of the second equilibrium are of lower concentration and C6H6O62- is
only produced in the second equilibrium, contributing to the lowest value. (38% correct)
65. The answer is “C.” This is a solubility rules question. We know ammonium, potassium, nitrates
and sodium are all always soluble. BaCO3 is not. (45% correct)
66. The answer is “C.” This is an ideal gas law problem. 1 mole of gas at STP is about 22.4 L. We
have 2 L, so we have about 1/11th of a mole. 4 g/(1/11th of a mole) is 44 g/mole. CO2 has the
closest molar mass to that. (41% correct)
67. The answer is “B.” Boiling is overcoming intermolecular forces. The principle intermolecular
force in water is hydrogen bonding. (52% correct)
68. The answer is “C.” Phase changes occur in plateaus on heating/cooling curves. Don’t overthink
it. (57% correct)
69. The answer is “A.” When we add 200 mL of solution and dilute it to a total volume of 600 mL, it
will be 1/3 the original concentration. 1/3 of 0.6 M is 0.2 M. For reference, Cl- will be 0.4 M, as
2 moles of Cl- will be produced from each mole of MgCl2.
70. The answer is “C.” Covalent network solids generally have the highest melting points of most
any substance. This is a tricky question, but hopefully you recognized SiO2 as glass and we know
that it has a remarkably high melting point.
71. The answer is “B.” Very difficult to answer without a calculator. 1/5th of a faraday is 1/5th of a
mole of electrons. Nickel has a 2+ charge, which means that 2 moles of electrons are required
to produce 1 mole of Nickel. So 1/5th of a mole of electrons, will produce 1/10th of a mole of
Nickel. Molar mass is 58.7 g, so you can produce 5.87 g. (13% correct)
72. The answer is “D.” Difficult question. We have to analyze each from a few different angles. Al
would precipitate in 3, as will Ba and Ni. CO32- will produce CO2 when reacting with acid.
Leaving us only with Na+. (35% correct)
73. The answer is “E.” As it is undergoing the phase change then it is in equilibrium. ΔG = 0. If we
consider this 0 = ΔH – TΔS. We can rearrange it to say ΔH = TΔS. (34% correct)
74. The answer is “B.” Adding acid to an ionic compound and liberating a gas is indicative of a
carbonate or bicarbonate and the gas produced is CO2. (27% correct)
75. The answer is “A.” The Ksp for this reaction would be [Zn2+][OH-]2, we know the concentration of
OH- = 2 x 10-6, the concentration of Zn2+ will be half of that due to the 2:1 ratio. So its
concentration will be 1 x 10-6. Plug in and solve. (1 x 10-6)(2 x 10-6)2 = 4 x 10-18. (21% correct)