Practice Test 3

Section I

AP® Chemistry Exam

SECTION I: Multiple-Choice Questions

DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO.

Instructions
At a Glance
Section I of this examination contains 60 multiple-choice questions. Fill in only the ovals for
Total Time numbers 1 through 60 on your answer sheet.
1 hour and 30 minutes
CALCULATORS MAY NOT BE USED IN THIS PART OF THE EXAMINATION.
Number of Questions
60 Indicate all of your answers to the multiple-choice questions on the answer sheet. No credit
Percent of Total Grade will be given for anything written in this exam booklet, but you may use the booklet for notes
50% or scratch work. After you have decided which of the suggested answers is best, completely
Writing Instrument fill in the corresponding oval on the answer sheet. Give only one answer to each question. If
Pencil required you change an answer, be sure that the previous mark is erased completely. Here is a sample
question and answer.
Sample Question Sample Answer

Chicago is a A B C D
(A) state
(B) city
(C) country
(D) continent

Use your time effectively, working as quickly as you can without losing accuracy. Do not
spend too much time on any one question. Go on to other questions and come back to the
ones you have not answered if you have time. It is not expected that everyone will know the
answers to all the multiple-choice questions.

About Guessing
Many candidates wonder whether or not to guess the answers to questions about which
they are not certain. Multiple-choice scores are based on the number of questions answered
correctly. Points are not deducted for incorrect answers, and no points are awarded for
unanswered questions. Because points are not deducted for incorrect answers, you are
encouraged to answer all multiple-choice questions. On any questions you do not know the
answer to, you should eliminate as many choices as you can, and then select the best answer
among the remaining choices.

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Practice Test 3 | 375

 Section I

CHEMISTRY
SECTION I
Time—1 hour and 30 minutes

1. AP Chem - New Exam One - Multiple Choice – Section I

[NOTE: all art piece highlighted in turquoise here can be found in PDF]

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376 | Cracking the AP Chemistry Exam

 Section I

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Practice Test 3 | 377

 Section I

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378 | Cracking the AP Chemistry Exam

 Section I

Acid Lewis Diagram Ka Metal Initial Temperature 98.0oC

HOBr 2.0 × 10–9 Water Initial Temperature 26.0oC
H O Br
Water + Metal Final Temperature 28.0oC
HOCl 3.0 × 10–8 Mass Metal 10.0 g
H O Cl
Mass Water 100. g

1. The Ka values and Lewis structures for two different 4. A piece of an unknown metal is heated to a high
oxoacids are listed above. Which of the following temperature, and then dropped into a cup of water.
statements correctly identifies the stronger acid and offers Given the data above and assuming no heat is lost to the
up the best justification? environment, what is the approximate specific heat of the
(A) HOBr, because bromine is larger than chlorine and metal? (Water has a specific heat of 4.2 J/goC.)
strongly repels the –OH group (A) 0.60 J/goC
(B) HOBr, because bromine’s electron cloud is more (B) 0.80 J/goC
polarizable than chlorine’s (C) 1.00 J/goC
(C) HOCl, because the OCl– ion has a stronger (D) 1.20 J/goC
attraction for protons than the OBr– ion
(D) HOCl, because chlorine is more electronegative
than bromine and weakens the H-O bond more
effectively Fe2O3 (s) + 3H2 (g)  3H2O (l) + 2Fe (s)

2. Approximately how many grams of oxygen are present in 5. What would the equilibrium constant expression, Kc, be
a 10.0 g sample of NaOH? for the above reaction?
(A) 2.00 g [Fe]2 [H 2 O]3
(A) K c =
(B) 4.00 g [Fe 2 O3 ][H 2 ]3
(C) 6.00 g [H 2 O]3
(D) 8.00 g (B) Kc =
[H 2 ]3
[H 2 ]3
(C) Kc =
[H 2 O]3
2Li (s) + 2H2O (l) → 2Li+ (aq) + H2 (g) + 2OH– (aq)
1
(D) Kc =
[H 2 ]3
3. A 3.50 g sample of lithium metal is dropped into a beaker
of water, causing the above reaction to occur. How many
liters of hydrogen gas are produced if this reaction takes
place at STP?
(A) 5.60 L
(B) 11.2 L
(C) 22.4 L
(D) 28.0 L

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 Section I

Questions 6-10 refer to the following standard reduction 8. A 2.0 A current is applied to beakers containing identical
potentials. volumes of each of the following 1.0 M solutions. In
beaker will the greatest mass of metal plate out?
(A) AgNO3 (aq)
Half Reaction Reduction (B) CuSO4 (aq)
Potential (C) FeCl2 (aq)
O2 (g) + 4H+ (aq) + 4e– → 2H2O (l) 1.23 V (D) AlBr3 (aq)
Ag (aq) + e → Ag (s)
+ –
0.80 V
Cu (aq) + 2e → Cu (s)
2+ –
0.34 V
Fe2+ (aq) + 2e– → Fe (s) –0.44 V
2H2O (l) + 2e → H2 (g) + 2OH
– –
–0.83 V
Power
Al (aq) + 3e → Al (s)
3+ –
–1.66 V Source
X Y

6. What would the cell potential be for a galvanic cell

constructed of Ag/Ag+ and Fe/Fe2+ half-cells?
(A) 0.36 V
(B) 1.16 V
(C) 1.24 V
(D) 2.04 V

7. What would the net ionic reaction be for the galvanic cell
described in question #6? 9. A current is run through a solution of pure water, and
gases are collected as shown in the above diagram. Which
(A) 2Ag+ (aq) + Fe (s) → 2Ag (s) + Fe2+ (aq) of the following correctly identifies the cathode and
(B) Fe2+ (aq) + 2Ag (s) → Fe (s) + 2Ag+ (aq) anode during the hydrolysis, along with identifying the
(C) Ag+ (aq) + Fe2+ (aq) → Ag (s) + Fe (s) gas present at each?
(D) 2Ag (s) + Fe (s) → 2Ag+ (aq) + Fe2+ (aq)
Electrode X Gas collected at
Identity Electrode X
(A) Cathode Hydrogen
(B) Anode Hydrogen
(C) Cathode Oxygen
(D) Anode Oxygen

10. Which of the following would NOT cause a reaction to

occur?
(A) Adding some aluminum pellets to a solution
containing Fe2+ ions
(B) Placing a copper strip into a solution containing
Ag+ ions
(C) Adding powdered iron to a solution containing
Cu2+ ions
(D) Dropping a silver coin into a solution containing
Al3+ ions

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380 | Cracking the AP Chemistry Exam

 Section I

Use the following information to answer questions 11-13. 14. A current of 4.0 A is run through an electrolytic cell for
a total of 2.0 minutes. How many coulombs of charge
passed through the cell during its operation?
(A) 2.0 C
(B) 8.0 C
Relative Number

(C) 30 C
of Electrons

(D) 480 C

15. Which of the following orbital diagrams shows the

correct electron configuration for an oxygen atom?

2p 2p
2,500 2,000 500 400 300 200 100 0
2s 2s
Binding Energy (eV)
1s 1s
(A) (C)
Peak 1 Peak 2 Peak 3 Peak 4 Peak 5
2300 eV 450 eV 150 eV 30 eV 5.0 eV
2p 2p
 he photoelectron spectrum for a neutral aluminum atom
T 2s 2s
is located above.
1s 1s
(B) (D)

11. The amount of energy necessary to remove an electron

from the 2p subshell is closest to which value?
(A) 450 eV CxHy (g) + O2 (g) → CO2 (g) + H2O (g)
(B) 150 eV
(C) 30 eV
(D) 5.0 eV 16. A hydrocarbon of an unknown formula consisting
of only hydrogen and carbon is combusted in excess
oxygen, producing 44.0 g of carbon dioxide and 18.0 g of
12. On a spectrum of an aluminum ion: water via the above unbalanced reaction. Which of the
(A) All peaks would be identical. following is a potential formula for the hydrocarbon?
(B) The peak furthest to the right be twice as tall. (A) CH4
(C) The two peaks furthest to the right would be (B) C2H3
missing. (C) C2H4
(D) All peaks would be half as tall. (D) C3H5

13. A different aluminum atom is exposed to incoming

radiation with an energy of 200 eV. Ejected electrons that
were originally in which orbital would have the lowest
kinetic energy?
(A) 1s
(B) 2s
(C) 2p
(D) 3p

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 Section I

19. How many moles of electrons are transferred in the

balanced equation?
(A) 2
(B) 3
(C) 4
Absorbance

(D) 6

20. How many grams of tin will react with 100. mL of

0.033 M K2Cr2O7?
(A) 0.40 g
(B) 1.2 g
(C) 2.4 g
(D) 3.6 g
200 300 400 500 600 700 800

Wavelength (nm)

Salt ∆Hsoln° (kJ/mol)

LiClO4 –26.55
17. C
 u2+ ions appear blue in solution, and the NO3–
ion is colorless. The absorbance of a Cu(NO3)2 NaClO4 13.88
solution is measured at various wavelengths using a KClO4 41.38
spectrophotometer. To determine the concentration of
a Cu(NO3)2 solution of unknown concentration, what
wavelength of light would produce the best results? 21. The enthalpy of solution for three different perchlorate
compounds is listed in the table above. Based on the data,
(A) 350 nm which of the following statements is correct?
(B) 500 nm
(C) 640 nm (A) As cation size increases, the rate at which the lattice
(D) 800 nm energy is changing exceeds the rate at which the
hydration energy is changing.
(B) The smaller the cation, the smaller the magnitude
Use the following information to answer questions 18-20. of the lattice energy will be.
(C) As cation size increases, the magnitude of the
Cr2O72– (aq) + 3Sn (s) + 14H+ (aq) → temperature change that occurs in the surrounding
2Cr3+ (aq) + 7H2O (l) + 3Sn2+ (aq) solution consistently increases.
(D) Of the three salts, only lithium perchlorate is fully
soluble in water, which is demonstrated by its
 solution of potassium dichromate, K2Cr2O7, is poured
A negative enthalpy of solution.
over a piece of solid tin, causing the oxidation-reduction
reaction above to occur.

Au+ (aq) + 2CN– (aq)  Au(CN)2– (aq) ∆H° = 242 kJ/mol

18. Which substance is oxidized, and which is reduced?
22. The above system is at equilibrium. Which of the
Oxidized Reduced
following would cause an immediate increase in the rate
(A) Cr2O7 Sn of the reverse reaction?
(B) H+ Cr2O7 (A) Adding some water
(C) Sn Cr2O7 (B) Adding some AuNO3 (aq)
(C) Increasing the pressure
(D) Cr2O7 H+ (D) Increasing the temperature

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382 | Cracking the AP Chemistry Exam

 Section I

2Ag+ (aq) + Cu (s) → 2Ag (s) + Cu2+ (aq) Ecell = +0.56 V 26. Which indicator would be the best to use to determine the
endpoint of the titration?

23. A silver/copper galvanic cell is set up, and the above Indicator pKa
reaction occurs. If all other variables were to remain the (A) Methyl Violet 0.80
same, what is one way to increase the cell potential? (B) Congo Red 4.0
(A) Increase the mass of the copper electrode (C) Thymol Blue 8.9
(B) Increase the mass of the silver electrode (D) Indigo Carmine 12.2
(C) Increase [Ag+]
(D) Increase [Cu2+]
27. If the hydrazoic acid were replaced with hydrocyanic acid
(Ka = 6.2 × 10–10) of identical concentration, which of the
Use the following information to answer questions 24-27. following changes would occur?
(A) Less NaOH would be required to reach the titration
Titration of HN3 with NaOH
endpoint.
14 (B) The initial pH would change as soon as any NaOH
12 is added will be greater.
10 (C) The pH of the solution at the 30.0 mL mark would
be higher.
8
(D) The pH at the equivalence point would be
pH

6
decreased.
4

0 Ion Ionization energy

0 5 10 15 20 25 30 35
(kJ/mol)
Volume of NaOH in mL
Al3+ 11500
HN3 (aq) + OH (aq) → N (aq) + H2O (l)
– 3– Mg 2+
7732
Na+ 4562
2 5.0 mL of hydrazoic acid, HN3 (Ka = 1.9 × 10–5), is
titrated with 0.50 M NaOH. The pH is measured during the
titration, producing the above graph. The equivalence point 28. The next ionization energy values for different ions of
is reached at a volume of 20.0 mL of NaOH added. three period 3 metals are listed above. The reason that the
aluminum ion has the greatest next ionization energy is:
(A) Aluminum metal is less chemically active than
24. What is the concentration of the HN3? magnesium or sodium.
(A) 0.40 M (B) The radius of the aluminum ion is the smallest.
(B) 0.50 M (C) The aluminum ion has the greatest number of
(C) 0.60 M unpaired electrons.
(D) 0.80 M (D) The aluminum ion experiences the smallest amount
of shielding.

25. At what volume of NaOH added would [N3–] = [HN3]?

(A) 5.0 mL
(B) 10.0 mL
(C) 20.0 mL
(D) 25.0 mL

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 Section I

NaCl (s) → Na+ (aq) + Cl– (aq) N2 (g) + 3H2 (g) → 2NH3 (g) ∆H° = x
2NH3 (g) + 4H2O (l) → 2NO2 (g) + 7H2 (g) ∆H° = y
H2O (l) → ½ O2 (g) + H2 (g) ∆H° = z
29. A sample of sodium chloride, NaCl, is dissolved fully in
water. Which diagram below is an accurate representation
of how the solution would look on the particulate level? 31. Given the enthalpy changes for the above reactions, what
would be the enthalpy change for the following reaction?

N2 (g) + 2O2 (g) → 2NO2 (g)

Na+ Cl–
(A) x + 2y + 2z
Cl –
Na+ (B) 4x – y – z
(C) x + y – 4z
(D) 2x + y – z
(A) (B)

CO2 (g) + H2 (g)  CO (g) + H2O (g) K = 5.0 × 10–3 at 25oC

Na+ Cl–
32. Using the above information, determine the equilibrium
Na+
Cl– constant for 2CO (g) + 2H2O (g)  2CO2 (g) + 2H2 (g).
(A) –1.0 × 10–4
(D)
(C) (B) 2.0 × 103
(C) 1.0 × 104
(D) 4.0 × 104
30. Which of the following expressions would accurately
give the magnitude for the density of a sample of helium
gas at STP?
(A) (4.0)
(0.0821)(273)

(B) (273)(0.0821)
4.0
(273)(4.0)
(C)
(0.0821)

(D) (4.0)(273)(0.0821)

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 Section I

Use the following information to answer questions 33-37. 35. Which of the following statements is true, according to
the graph?
(A) The intramolecular forces are strongest during
200
D
phase A.
(B) The heat of vaporization exceeds the heat of fusion.
(C) The strength of the intermolecular forces is
C
unaffected by the addition of energy.
150 (D) The average molecular speed increases throughout
the heating process.

B
100
36. How much energy would be required to melt a separate
1.0 g sample of the substance?
(A) 100 J
(B) 200 J
A
50 (C) 300 J
(D) 400 J

37. What is the approximate specific heat of the substance in

200 400 600 800 1,000 1,200 1,400 1,800
its liquid phase?
1,600
(A) 2.0 J/goC
 2.0 g sample of a solid covalent substance is placed
A (B) 4.0 J/goC
inside an enclosed chamber, and heat is added at a constant (C) 6.0 J/goC
rate. The temperature of the substance is tracked as heat is (D) 8.0 J/goC
added, producing the above graph.

33. At which point on the graph will the substance exist in

both its solid and liquid phase simultaneously?
(A) Point A
(B) Point B
(C) Point C
(D) Point D

34. At which point(s) on the graph will intermolecular forces

be the weakest?"
(A) Point A only
(B) Points B and D
(C) Point D only
(D) Intermolecular forces are present at all times.

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 Section I

HF F HF H NaCl (aq)

HF HF
HF F
H HF
HF HF
Zn Pb

Zn2+ Pb2+
HF (aq)  H+ (aq) + F– (aq)

38. HF, is a weak acid with a Ka value of 7.2 × 10–4. The box Pb2+ (aq) + Zn (s) → Pb (s) + Zn2+ (aq)
above represents a particulate-level view of a HF solution
of known concentration. If some water is added, which
of the following options would represent a particulate [Pb2+] [Zn2+] Mass Pb Mass Zn
representation of the diluted solution? electrode electrode
Battery X 1.0 M 1.0 M 10. g 10. g
HFH H F Battery Y 2.0 M 2.0 M 20. g 20. g
HF HF HF HF
HF
F HF HF F HF H
HF HF HF
HF
H HF 39. Two batteries are constructed via the above diagram.
HF HF F The concentration of the solutions and the mass of the
(A) (C) electrodes are identified in the data table below the
diagram. How would the voltage and the battery life for
F the two batteries compare?
HF H H F
HF HF H H
H H Voltage Battery Life
H HF F HF F FF
HF F (A) X <Y X <Y
F H H H H
HF F (B) X <Y X =Y
HF F H F F (C) X =Y X =Y
(B) (D) (D) X =Y X <Y

40. Which of the four substances listed below would have the
highest melting point?
(A) KCl
(B) CaBr2
(C) MgO
(D) C6H12O6

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386 | Cracking the AP Chemistry Exam

 Section I

Use the following information to answer questions 41-43. 43. After the stopcocks have been opened, the entire system
is heated. Choose the graph below that correctly shows
how the pressure would change as the temperature is
increased.

Kr H2O CO2

PKr = 1.0 atm PH2O = 2.0 atm PCO2 = 3.0 atm P P

 hree identical 1.0 L containers filled with different gases

T
are connected using glass tubes. The stopcocks at the top T
of each flask are initially closed and all three containers T
(A) (C)
are held at 125oC.

41. Which gas particles are moving the fastest?

(A) Kr P P
(B) H 2O
(C) CO2
(D) All gas particles are moving at the same speed
T T
(B) (D)
42. Assuming the volume of the connecting tubes is
negligible and that temperature remains constant, what
would the total pressure of the system be after all three
stopcocks are opened and the gases fully mix?
(A) 2.0 atm
(B) 4.0 atm
(C) 6.0 atm
(D) 8.0 atm

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 Section I

44. A 1.0 M solution of which of the following would have 2NO2 (g)  2NO (g) + O2 (g)
the highest conductivity?
(A) C2H5OH (aq) 47. At 0oC, the partial pressure of each gas above in an
(B) NH4Cl (aq) equilibrium system are PNO2 = 0.60 atm, PNO = 0.30 atm,
(C) PF3 (aq) and PO2 = 0.20 atm. What is Kp for this reaction at 0oC?
(D) Na2CO3 (aq)
(A) 0.05
(B) 0.10
(C) 10.
Halogen Boiling Point (D) 20.
(oC)
F2 –188 Use the following information to answer questions 48-50.
Cl2 –35
H O
Br2 59 ∠x ∠y
I2 184 H C C N H
∠z
H H
45. The boiling point trend observed in the halogens is due to
which of the following trends increasing going down the  Lewis diagram of the acetamide molecule, CH3CONH2,
A
group? is drawn above. Note the bond angles are not drawn to
(A) Molar mass scale.
(B) First ionization energy
(C) Electron cloud polarizability
(D) Electronegativity 48. Identify the bond angles on the diagram from greatest to
smallest.
(A) X >Y > Z
H H
(B) X > Z >Y
C C + 3( O O ) 2( O C O ) + 2( H O H ) (C) Z > X >Y
(D) Y>X>Z
H H
49. How many pi bonds are present in an acetamide
Bond Enthalpy Bond Enthalpy molecule?
(kJ/mol) (kJ/mol) (A) 0
C-H 410 C=O 800 (B) 1
C=C 720 H-O 470 (C) 2
(D) 3
O=O 500

50. What is the strongest type of intermolecular force present

46. Given the bond enthalpy values in the data table above, between acetamide molecules in an aqueous solution?
determine the enthalpy change for the reaction above it. (A) London dispersion forces
(A) –1220 kJ/mol (B) Hydrogen bonding
(B) – 400 kJ/mol (C) Ionic bonding
(C) 400 kJ/mol (D) Covalent bonding
(D) 1220 kJ/mol

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 Section I

51. Chlorous acid, HClO2, has a Ka value of 1.0 × 10–2. What 54. If some additional NH3 (g) is injected into the flask,
would the pH of a solution of 1.0 M sodium chlorite, which of the following options correctly predicts the
NaClO2, be? reaction shift and what would happen to the concentration
of NH4HS?
(A) 4
(B) 6 Shift [NH4HS]
(C) 8 (A) Left Increase
(D) 10 (B) Left No Change
(C) Right Decrease
(D) None No Change
SO2 (g) + O3 (g) → SO3 (g) + O2 (g)

55. If the temperature of the flask were to be increased to

Trial [SO2](M) [O3](M) Initial Rate (M/s)
313 K, which of the following identifies what would
1 0.10 0.10 0.075 happen to the amount of NH4HS present at equilibrium
2 0.10 0.20 0.075 and correctly explains why?
3 0.20 0.10 0.300 (A) Increase because both reaction rates have been
permanently increased
52. The above reaction is run three separate times, varying (B) Decrease because the value for K has increased
the initial concentration of both reactants as shown. The (C) Decrease because the reaction is becoming more
initial rate is shown for each reaction. What is the rate disordered
law for the reaction? (D) Remain the same because it is a solid and
unaffected by reaction shifts
(A) Rate = k[SO2][O3]
(B) Rate = k[SO2]
(C) Rate = k[SO2]2 56. If the reaction were to be repeated at 298 K using the
(D) Rate = k[O3]2 same initial amount of NH4HS, but in a 500 mL flask,
how would that affect the concentration of NH3 at
equilibrium compared to the trial in the 250 mL flask?
Use the following information to answer questions 53-56.
(A) It would be unchanged.
(B) It would decrease by a factor of four.
NH4HS (s)  H2S (g) + NH3 (g) At 298 K, Kc = 9.0 × 10 –2
(C) It would decrease by a factor of two.
∆H° = +91 kJ/molrxn
(D) It would increase by a factor of two.

 ome solid NH4HS is placed in a sealed and evacuated

S
250 mL flask at 298 K, and the above decomposition
reaction is allowed to reach equilibrium.

53. Calculate the concentration of the NH3 (g) at equilibrium.

(A) 9.0 × 10–2 M
(B) 3.0 × 10–1 M
(C) 1.0 × 102 M
(D) 9.0 × 102 M

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 Section I

59. Which of the following diagrams correctly demonstrates

Si Si Si Si the permanent dipole attractions between two molecules
of oxygen difluoride, OF2? Note that the dashed lines are
Si x Si Si representative of attractive intermolecular forces.
Si Si Si Si

O O
F F F F
57. A semiconductor with a silicon lattice is doped by the
addition of another element, symbolized by the letter X
in the above diagram. Which of the following statements O O
best describes the possible identity of the element as well F F F F
as the type of doping that is occurring?
(A) (C)
(A) Boron, which has less valence electrons than silicon
and creates positive “holes” in the lattice
(B) Phosphorus, which has extra valence electrons and
creates a mobile negative charge in the lattice O O
(C) Aluminum, which has metalloid properties that F F F F
lend to increased conductivity when added to a
semiconductor
(D) Carbon, which has an equal number of valence O O
electrons as silicon and strengths the conducting F F F F
lattice
(B) (D)
58. What is the oxidation state on the sulfur atom in the
compound S2Cl2?
(A) –2
(B) –1 60. Which of the following reactions would have the most
(C) 0 negative value for DS°?
(D) +1 (A) 2NH3 (g) → N2 (g) + 3H2 (g)
(B) H2O (1) → H2O (g)
(C) CaO (s) + CO2 (g) → CaCO3 (s)
(D) MgCl2 (s) + H2O (1) → MgO (s) + 2HCl (g)

END OF SECTION I

390 | Cracking the AP Chemistry Exam

 Section II

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 Section II

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392 | Cracking the AP Chemistry Exam

 Section II

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Practice Test 3 | 393

 Section II

CHEMISTRY
Section II
7 Questions
(Total time—105 minutes)

YOU MAY USE YOUR CALCULATOR FOR THIS SECTION

Directions: Questions 1-3 are long free-response questions that require about 23 minutes each to answer and are worth 10 points
each. Questions 4-7 are short free-response questions that require about 9 minutes each to answer and are worth 4 points each.

Write your response in the space provided following each question. Examples and equations may be included in your responses
where appropriate. For calculations, clearly show the method used and the steps involved in arriving at your answers. You must
show your work to receive credit for your answer. Pay attention to significant figures.

CaCl2 (aq) + (NH4)2C2O4 (aq) → CaC2O4 (s) + 2NH4Cl (aq)

1. Most vitamin tablets consist of not only the active ingredient, but also other ingredients that are there to bind the vitamin
together or coat it for easier swallowing. A calcium tablet with a mass of 1.49 g is crushed, and then dissolved in some
concentrated HCl, creating aqueous calcium chloride. The tablet solution is then mixed with excess ammonium oxalate in a
basic environment, causing calcium oxalate to precipitate.
(a) Describe a method to fully separate the precipitate from the solution and accurately measure its mass.

(b) The final mass of the CaC2O4 is determined to be 1.64 g.

(i) How many moles of calcium are present in the precipitate?
(ii) What is the mass percent of calcium in the original vitamin tablet?

(c) CaC2O4 has a Ksp value of 1.9 × 10–9 and dissociates in solution as follows.
CaC2O4 (s)  Ca2+ (aq) + C2O42– (aq)

(i) What is the concentration of Ca2+ ions and C2O42– ions in a saturated solution of CaC2O4?
(ii) If some of the water evaporated from a saturated solution of CaC2O4, how would that effect the concentration of the
ions you determined in part (c)(i)? Justify your answer.

The results do not match the accepted value of calcium in the tablet provided by the manufacturer. Upon reviewing the
reaction, it was determined that the final product was not, in fact, pure calcium oxalate, but was instead a hydrate of
calcium oxalate.

(d) Would not accounting for the water of hydration cause the calcium value in the tablet to be artificially high or artificially
low? Why?

(e) A 5.00 g sample of the calcium oxalate hydrate is heated several times, resulting in a final mass for the anhydrous salt of
4.38 g.
(i) How many moles of water were present in the sample?
(ii) What is the hydration coefficient?

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394 | Cracking the AP Chemistry Exam

 Section II

NaF (s)  Na+ (aq) + F– (aq)

2. Sodium fluoride is the active ingredient in toothpaste that helps prevent tooth decay. One of the important aspects of sodium
fluoride is that it is completely soluble in water, and will dissociate fully.
(a) What are the forces that exist between sodium fluoride and water molecules that allow for this dissociation to occur?

(b) Which ion has the larger size- Na+ or F–? Justify your answer.

(c) The below beaker is filled with water molecules. In the beaker, correctly draw the location of the Na+ and F– ions in a
dissolved solution of sodium fluoride. Make sure each ion is labeled clearly.

(d) 5.00 g of NaF is dissolved into 50.0 mL of water, and the temperature of the water decreases by 0.52oC. The specific
heat and density of solution are identical to that of pure water; 4.18 J/goC and 1.0 g/mL, respectively.
(i) How much energy is lost by the solution during the dissolution process?
(ii) What is the enthalpy of solution, in kJ/mol, for the dissolution of sodium fluoride?
(iii) For the dissolution of sodium fluoride, which value has a greater magnitude—the lattice energy of sodium fluoride,
or the hydration energy between sodium fluoride and water? How do you know?

(e) How would you expect the magnitude of the hydration energy for sodium fluoride compare to that of potassium
chloride, KCl? Justify your answer.

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Practice Test 3 | 395

 Section II

HCH3H5O3 (aq)  H+ (aq) + CH3H5O3– (aq) Ka = 1.38 × 10–4

3. Lactic acid is an acid found in many dairy-related products.

(a) Write the equilibrium constant expression, Ka, for lactic acid.

(b) (i) The pH of an 0.50 M solution of lactic acid is found to be 2.08. Calculate the percent dissociation of the 0.50 M
lactic acid solution.
(ii) If the 0.50 M solution from part (i) were to be diluted, how would that affect the percent dissociation, if at all?
Justify your answer.

(c) Lactic acid is the active ingredient in sour cream which makes it taste sour. A sour cream sample with a volume of
500. mL is titrated, and the lactic acid present in it is found to have concentration of 0.113 M. If the sour cream sample
has a density of 1.0 g/mL, what is the percent by mass of lactic acid present in the sour cream?

(d) To control the pH level of lactic acid containing substances, sodium lactate, NaC3H5O3, is often used.
(i) How many moles of sodium lactate would need to be added to 100. mL of 0.10 M lactic acid to create a buffer with
a pH of 4.0?
(ii) Adding a small amount of which of the following chemicals to a solution of lactic acid would also create a buffer
solution? Justify your answer using a chemical reaction.

HCl NaOH KCl

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396 | Cracking the AP Chemistry Exam

 Section II

4. Many foods are dyed various colors to make them more aesthetically pleasing. The dyes are often complex organic
compounds, including on that is commercially called Brilliant Blue FCF, which can be abbreviated as BB. When BB reacts
with the active ingredient in bleach, the hypochlorite ion (ClO–), the color will fade over time. Thus, the rate of reaction can be
determined by using a colorimeter to measure the rate at which the BB fades.

To determine the reaction order for both BB and ClO– in this reaction, three trials are run at 25oC and the rate of reaction is
measured in each.

Trial [BB] (M) [ClO–] (M) Rate (M/s)

1 1.5 × 10 –3
1.5 × 10 –3
3.3 × 10–3
2 2.0 × 10–3 1.5 × 10–3 4.4 × 10–3
3 3.0 × 10–3 2.5 × 10–3 1.1 × 10–2

(a) What is the reaction order with respect to:

(i) BB
(ii) ClO–

(b) Calculate the rate constant for the reaction between BB and ClO– at 25oC. Include units.

NH3 C4H10 CH3OCH3

PNH3= 7,600 mmHg PC4H10= 2,200 mmHg PCH3OCH3= 200 mmHg

5. Three different liquids are placed in three sealed flasks of identical volume as shown above. All of the flasks are held at a
constant temperature of 25oC, and the vapor pressure of each gas is listed below the flask.

(a) Which liquid has the strongest intermolecular forces? Justify your answer on a particular level.

(b) If the temperature of each of the flasks were to be increased, what effect would that have on the vapor pressure, if any?
Why?

(c) (i) Are the gases present in each flask least likely to behave ideally at very low or very high temperatures? Explain
your reasoning.
(ii) Which substance would show the greatest deviation from ideal behaviors under the conditions you chose in (c)(i)?
Justify your answer.

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Practice Test 3 | 397

 Section II

6. Use the below diagram of the chlorate ion, ClO3–, to answer the following questions as needed.

Oy

Cl
Ox Oz

(a) What is the oxidation state on the chlorine atom in the chlorate ion? Show any necessary calculations.

(b) Calculate the formal charge on each atom in the chlorate ion. Note that each oxygen atom should be clearly labeled to
match the subscripts in the diagram.

(c) Is the Cl-Ox bond shorter than, longer than, or the same length as the Cl-Oy bond? Justify your answer.

(d) Chlorine atoms can expand their octet, but oxygen atoms cannot. Why?

7. The Br-Br bond in a bromine molecule has a bond energy of 193 kJ/mol.

(a) (i) How much energy, in Joules, is required to break the bond in a single Br molecule?
(ii) What wavelength of light is necessary to break a single Br-Br bond?

(b) Is the wavelength of light necessary to break a F-F bond shorter than, longer than, or the same as the wavelength of light
necessary to break the Br-Br bond? Justify your answer.

STOP

END OF EXAM

398 | Cracking the AP Chemistry Exam

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20. A B C D 40. A B C D 60 A B C D