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AP Chemistry
Practice Units 1-5
Multiple Choice (No calculator)
Questions 1-3 refer to the following molecules.
(A) CO2
(B) CH4
(C) HF
(D) PH3
1. Contains only two -bonds
2.
Has the highest dipole moment
3.
Has a molecular geometry that is trigonal pyramidal
Name _________________________
Period _____
11. Which of the following best explains why the normal boiling
point of CCI4(I) (350 K) is higher than the normal boiling
point of CF4(I) (145 K)?
(A) The C-CI bonds in CCI4 are less polar than the C-F
bonds in CF4.
(B) The C-CI bonds in CCI4 are weaker than the C-F
bonds in CF4.
(C) The mass of the CCI4 molecule is greater than that of
the CF4 molecule.
(D) The electron cloud of the CCI4 molecule is more
polarizable than that of the CF4 molecule.
Questions 4-6 refer to neutral atoms for which the atomic
orbitals are represented below
(A) 1s()
(B) 1s() 2s() 2p()()( )
(C) 1s() 2s() 2p()()()
(D) [Ar] 4s() 3d()()()()()
4. contains the most valence electrons
12. At which of the following temperatures and pressures would
a real gas be most likely to deviate from ideal behavior?
Temperature (K) Pressure (atm)
(A)
100
50
(B)
200
5
(C)
300
0.01
(D)
500
0.01
5.
is diamagnetic
6.
is a transition metal
13. After 195 days, a 10.0 g sample of pure 95Zr has decayed
to the extent that only 2.50 g of the original 95Zr remains.
The half-life of 95Zr is closest to
(A) 195 days
(B) 97.5 days
(C) 65.0 days
(D) 48.8 days
Questions 7-8 refer to a various points in time during an
experiment conducted at 1.0 atm. Heat is added at a constant
rate to a sample of a pure substance that is solid at time to.
The graph below shows the temperature of the sample as a
function of time.
7.
(A) t1
(B) t2
(C) t3
(D) t5
Time when solid and liquid states are in equilibrium.
8.
Time when the temperature of the substance is between its
melting point and its boiling point
9.
Three gases in the amounts shown in the table above are
added to a previously evacuated rigid tank.
Gas
Ar
CH4
N2
Amount
0.35 mol
0.90 mol
0.25 mol
If the total pressure in the tank is 3.0 atm at 25oC, the
partial pressure of CH4(g) in the tank is closest to
(A) 0.9 atm (B) 1.5 mol (C) 1.8 mol (D) 3.0 mol
10. Which of the following substances exhibits significant
hydrogen bonding in the liquid state?
(A) CH2F2 (B) N2H4
(C) C2H4
(D) CH3OCH3
14. The first seven ionization energies of element X are shown
in the table below.
1st
2nd
3rd
4th
5th
6th
7th
Ionization
Energy
787 1,580 3,200 4,400 16,000 20,000 24,000
(kJ•mol-1)
On the basis of these data, element X is most likely a
member of which of the following groups of elements?
(A) Alkaline earth metals (B) Boron group
(C) Carbon group
(D) Nitrogen group
15. Which of the following particles is emitted by an atom of
39 Ca when it decays to produce an atom of 39 Sc?
20
21
(A) 10n
(B) 11H
(C) (D) +
16. At approximately what temperature will 40. g of argon gas
at 1.0 atm occupy a volume of 11.2 L?
(A) 600 K (B) 550 K (C) 270 K (D) 140 K
17. Which of the following 0.25 M aqueous solutions has the
highest boiling point at 1.0 atm?
(A) CaCl2 (B) Na2SO4 (C) NaCl
(D) C6H12O6
18. An aqueous solution contains 11.0 % RbCl by mass. From
the following list, what is needed to determine the molarity?
I. Mass of the sample
II. Volume of the sample
III. Temperature of the sample
(A) I only
(B) II only (C) III only (D) I and II only
19. Heat energy is added slowly to a pure covalent network
compound at its melting point. About half of the solid melts
to become a liquid. Which of the following must be true
about this process?
(A) Covalent bonds are broken as the solid melts.
(B) The temperature of the solid/liquid mixture remains the
same while heat is being added.
(C) The volume of the compound increases as the solid
melts to become a liquid.
(D) The average kinetic energy of the molecules become
greater as the molecules leave the solid state and
enter the liquid state.
a.
Draw the complete Lewis electron-dot diagram for
ethyne, C2H2.
b.
Which of the four molecules contains the shortest
carbon-to-carbon bond? Explain.
c.
A Lewis electron-dot diagram of a molecule of
ethanoic acid is given below. The carbon atoms in the
molecule are labeled x and y, respectively.
20. Which of the following molecules contains bonds that have
a bond order of 1.5?
(A) N2
(B) O3
(C) NH3
(D) CO2
Identify the geometry of the arrangement of atoms
bonded to each of the following.
(1) Carbon x
21. In which of the following are the chemical species correctly
ordered from smallest radius to largest radius?
(A) B < C < N
(B) At < Xe < Kr
(C) CI < S < S2(D) Na < Na+ < K
(2) Carbon y
22. Of the following elements, which would be expected to
have chemical properties most similar to those of sulfur, S?
(A) Br
(B) CI
(C) P
(D) Se
d.
Energy is required to boil ethanol. Consider the
statement “As ethanol boils, energy goes into breaking
C−C bonds, C−H bonds, C−O bonds, and O−H
bonds.” Is the statement true or false? Justify your
answer.
e.
Identify a compound from the table above that is
nonpolar. Justify your answer.
f.
Ethanol is completely soluble in water, whereas
ethanethiol has limited solubility in water. Account for
the difference in solubilities between the two
compounds in terms of intermolecular forces.
23. Of the following gases, which has the greatest average
molecular speed at 298 K?
(A) Cl2
(B) NO
(C) H2S
(D) HCN
24. Types of hybridization exhibited by carbon atoms in a
molecule of propyne, CH3CHCH2, include which of the
following?
I. sp
II. sp2
III. sp3
(A) I only
(B) II only (C) III only (D) I and II only
25. In which of the following processes are covalent bonds
broken?
(A) Solid silver melts.
(B) Solid potassium chloride melts.
(C) Solid carbon (graphite) sublimes.
(D) Solid iodine sublimes.
2.
b.
Free Response (Calculator)
1.
Use the information in the table below to respond to the
statements and questions that follow. Your answers should
be in terms of principles of molecular structure and
intermolecular forces.
Compound
Formula
Lewis Electron-Dot
Diagram
Ethanethiol
CH3CH2SH
Ethane
CH3CH3
Ethanol
CH3CH2OH
2 Al(s) + 3 Zn2+ → 2 Al3+ + 3 Zn(s)
Respond to the following statements and questions that
relate to the species and the reaction represented above.
a. Write the complete electron configuration
(e.g., 1s2 2s2 . . .) for Zn2+.
3.
Which species, Zn or Zn2+, has the greater ionization
energy? Justify your answer.
Answer the following using chemical concepts and
principles of the behavior of gases.
a. A metal cylinder with a volume of 5.25 L contains 3.22
g of He(g) and 11.56 g of N2(g) at 15.0oC.
(1) Calculate the total pressure.
(2) Calculate the partial pressure of N2(g).
b.
A 1.50 L container holds a 9.62 g sample of an
unknown gaseous saturated hydrocarbon at 30oC and
3.62 atm.
(1) Calculate the density of the gas.
c.
In the SO2 molecule, both of the bonds between sulfur
and oxygen have the same length. Explain this
observation, supporting your explanation by drawing in
the box below a Lewis electron-dot diagram (or
diagrams) for the SO2 molecule
d.
On the basis of your Lewis electron-dot diagram(s) in
part c, identify the hybridization of the sulfur atom in
the SO2 molecule.
(2) Calculate the molar mass of the gas.
(3) Write the formula of the hydrocarbon.
(4) Calculate the root-mean-square speed of the gas
molecules in the container at 30'C.
4.
Answer each of the following using principles of atomic or
molecular structure, and/or intermolecular or intramolecular
forces
a. Explain why the H-O-H bond angle in H2O is less than
the H-N-H bond angles in NH3, as shown in the table
below.
H–O–H Bond Angle in H2O
H–N–H Bond Angle in NH3
104.5o
107o
b.
c.
6.
Answer the following questions about the structures of ions
that contain only sulfur and fluorine.
a. The compounds SF4 and BF3 react to form an ionic
compound according to the following equation.
SF4 + BF3  SF3BF4
(1) Draw a complete Lewis structure for the SF3+
cation in SF3BF4.
Explain why the radius of the Br atom is less than the
radius of the Br- ion, as shown in the table below.
Radius of Br
Radius of Br0.111 nm
0.196 nm
(2) Identify the type of hybridization exhibited by
sulfur in the SF3+ cation.
(3) Identify the geometry of the SF3+ cation that is
consistent with the Lewis structure drawn in part
a(1).
Explain why the dipole moment of HI is less than the
dipole moment of HCI, as shown in the table below.
Dipole Moment of HI
Dipole Moment of HCl
0.42 debye
1.08 debyes
Explain why the normal boiling point of Ne is less than
the normal boiling point of Kr, as shown in the table
below.
Normal Boiling Point of Ne
Normal Boiling Point of Kr
27 K
121 K
(4) Predict whether the F-S-F bond angle in the SF3+
cation is larger than, equal to, or smaller than
109.5°. Justify your answer.
d.
5.
Answer the following questions, which pertain to binary
compounds.
a. In the box provided, draw a complete Lewis electrondot diagram for the IF3 molecule.
b.
The compounds SF4 and CsF react to form an ionic
compound according to the following equation.
SF4 + CsF  CsSF5
(1) Draw a complete Lewis structure for the SF5anion in CsSF5.
(2) Identify the type of hybridization exhibited by
sulfur in the SF5- anion.
b.
On the basis of the Lewis electron-dot diagram that
you drew in part a, predict the molecular geometry of
the IF3 molecule.
(3) Identify the geometry of the SF5- anion that is
consistent with the Lewis structure drawn in part
b(1).
(4) Identify the oxidation number of sulfur in the
compound CsSF5.
AP Chemistry
Practice Units 6-9
Name _________________________
Period _____
Multiple Choice (No calculator)
What mass of KBr (MM = 119 g mol-1) is required to make
500. mL of a 0.200 M KBr solution?
(A) 0.595 g
(B) 1.19 g
(C) 2.50 g
(D) 11.9 g
11. A reaction is spontaneous below 400 K but is not
spontaneous above 400 K. If So for the reaction is –50.0
J•mol-1 K-1, then the value of Ho for the reaction is
(A) -50.0 kJ mol-1
(B) -20 kJ mol-1
(C) -0.050 kJ mol-1
(D) 2.0 x 104 kJ mol-1
2.
The standard enthalpy of formation, Hof, of HI(g) is +26 kJ
mol-1. What is the approximate mass of HI(g) that is
decompose into H2(g) and I2(s) to release 500 kJ of energy?
(A) 250 g
(B) 650 g
(C) 1,300 g
(D) 2,500 g
12.
_ Au3+ + _I-  _Au(s) + _I2(s)
When the equation is balanced using the lowest wholenumber coefficients, the coefficient for I2(s) is
(A) 8
(B) 6
(C) 4
(D) 3
13.
3.
_CH3OCH3(g) + _O2(g)  _CO2(g) + H2O(g)
When the equation above is balanced using the lowest
whole-number coefficients, the coefficient for CO2(g) is
(A) 6
(B) 4
(C) 3
(D) 2
ZX+Y
A pure substance Z decomposes into two products, X and
Y, as shown by the equation. Which of the following graphs
of the concentration of Z versus time is consistent with the
rate of the reaction being second order with respect to Z?
(A)
(B)
4.
What mass of Cu(s) would be produced if 0.50 mol of
Cu2O(s) was reduced completely with excess H2(g)?
(A) 13 g
(B) 25 g
(C) 32 g
(D) 64 g
1.
5.
Which of the following is a formula of a ketone?
(A) CH3–CO–CH3
(B) CH3–CH2–COOH
(C) CH3–CH2–CH2OH
(D) CH3–CH2–O–CH3
6.
Which of the following would produce the MOST mass of
CO2 if completely burned in excess oxygen gas?
(A) 10.0 g CH4
(B) 10.0 g CH3OH
(C) 10.0 g C2H4
(D) 10.0 g C2H6
Questions 7-9 refer to a galvanic cell constructed using two
half-cells and based on the two half-reactions below.
Zn2+ + 2 e-  Zn(s)
Eo = -0.76 V
Fe3+ + e-  Fe2+
Eo = 0.77 V
7. As the cell operates, ionic species that are found in the halfcell containing the cathode include which of the following?
I. Zn2+
II. Fe2+
III. Fe3+
(A) I only
(B) II only (C) III only (D) II and III
8.
What is the standard cell potential for the galvanic cell?
(A) -0.01 V
(B) 0.01 V
(C) 1.53 V
(D) 2.30 V
9.
What is the oxidizing agent for the forward reaction?
(A) Zn2+
(B) Zn
(C) Fe2+
(D) Fe3+
10.
C(diamond)  C(graphite)
For the reaction represented above, the standard Gibbs
free energy change, Go298, is negative. However the
reaction does not occur at 298 K and 1.00 atm. This is
probably because the following value is extremely large.
(A) S
(B) H
(C) G
(D) Ea
(C)
14.
(D)
CS2(l) + 3 O2(g)  CO2(g) + 2 SO2(g)
When 0.60 mol of CS2(l) reacts as completely as possible
with 1.5 mol of O2(g) according to the equation above, the
total number of moles of SO2(g) is
(A) 0.60 mol (B) 1.0 mol (C) 1.2 mol (D) 1.5 mol
Questions 15-16 refer to an experiment to determine the heat of
fusion of ice. A student used a calorimeter consisting of a
polystyrene cup and a thermometer. The cup was weighed,
then filled halfway with warm water, then weighed again.
The temperature of the water was measured, and some ice
cubes from a 0oC ice bath were added to the cup. The
mixture was gently stirred as the ice melted, and the lowest
temperature reached by the water in the cup was recorded.
The cup and its contents were weighed again.
15. The purpose of weighing the cup and its contents again at
the end of the experiment was to
(A) determine the mass of ice that was added
(B) determine the mass of the thermometer
(C) determine the mass of water that evaporated
(D) verify the mass of water that was cooled
16. A student weighs out 0.0154 mol of pure, dry NaCI in order
to prepare a 0.154 M NaCI solution. Of the following
pieces of laboratory equipment, which would be most
essential for preparing the solution?
(A) 50 mL volumetric pipet
(B) 100 mL Erlenmeyer flask
(C) 100 mL graduated beaker
(D) 100 mL volumetric flask
17. Suppose that during the experiment, a significant amount
of water from the ice bath adhered to the ice cubes. How
does this affect the calculated heat of fusion of ice?
(A) The calculated value is too large because less warm
water had to be cooled
(B) The calculated value is too large because more cold
water had to be heated
(C) The calculated value is too small because less ice was
added than the student assumed
(D) The calculated value is too small because the total
mass of the calorimeter contents was too large.
25.
8 H2(g) + S8(s)  8 H2S(g)
When 0.1 mol of S8(s) reacts completely with excess H2(g)
according to the equation above, the volume of H2S(g),
measured at 0oC and 1.00 atm, produced is closest to
(A) 30 L
(B) 20 L
(C) 10 L
(D) 5 L
Free Response (Calculator)
1.
18. A steady electric current is passed through molten MgCl2
for exactly 1.00 hour, producing 243 g of Mg metal. If the
same current is passed through AlCl3 for 1.00 hour, the
mass of Al metal produced is closest to
(A) 27.0 g (B) 54.0 g (C) 120. g (D) 180. g
19. What is the empirical formula of a hydrocarbon that is 20 %
hydrogen by mass?
(A) CH3
(B) C2H5
(C) C3H4
(D) C4H9
20.
5 Fe2+ + MnO4- + 8 H+ → 5 Fe3+ + Mn2+ + 4 H2O
A galvanic cell and the balanced equation for the
spontaneous cell reaction are shown above. The two
reduction half-reactions for the overall reaction that occurs
in the cell are shown below.
Half-Reaction
E° (V) at 298 K
Fe3+ + e-  Fe2+
+ 0.77
MnO4- + 8 H+ + 5 e-  Mn2+ + 4 H2O
+1.49
a. On the diagram, clearly label the cathode.
b. Calculate the value of the standard potential, E°, for
the spontaneous cell reaction.
Pb(s)  Pb(l)
Which of the following is true for the process represented
above at 327oC and 1 atm; the normal melting point for Pb(s)
(A) H = 0 (B) S = 0 (C) G = 0 (D) H/S = 0
21. Equal volumes of 0.15 M HCl and 0.25 M HCl are mixed.
The molarity of the resulting solution is
(A) 0.25 M HCl
(B) 0.20 M HCl
(C) 0.15 M HCl
(D) 0.10 M HCl
22.
2 HClO + 3 O2  2 HClO4
As the reaction represented above proceeds to the right,
the oxidation number of chlorine changes from
(A) -1 to +5
(B) +1 to +5
(C) +1 to +7
(D) +3 to +7
c.
How many moles of electrons are transferred when
1.0 mol of MnO4- is consumed in the overall reaction?
d.
Calculate the value of the equilibrium constant Keq for
the cell reaction at 25°C. Explain what the magnitude
of Keq tells you about the extent of the reaction.
Three solutions, one containing Fe2+, one containing
MnO4-, and one containing H+, are mixed in a beaker and
allowed to react. The initial concentrations of the species in
the mixture are 0.60 M Fe2+, 0.10 M MnO4-, and 1.0 M H+.
e. Which has the higher concentration, Mn2+ or MnO4-,
when the reaction mixture has come to equilibrium?
Explain.
23. A large piece of wood burns slowly, but sawdust combusts
explosively. The primary reason for the difference is that
compared with a large piece of wood sawdust
(A) has a greater surface area per kilogram
(B) has a greater carbon content per kilogram
(C) absorbs more atmospheric moisture per kilogram
(D) contains more compounds that act as catalysts for
combustion
f.
24. When a solution is formed by adding some methanol,
CH3OH, to water, processes that are exothermic include
which of the following?
I. Methanol molecules move water molecules apart
as the methanol goes into solution.
II. Water molecules move methanol molecules apart
as the methanol goes into solution.
III. Intermolecular attractions form between
molecules of water and methanol as the methanol
goes into solution.
(A) I only
(B) II only (C) III only (D) I and II only
2.
When the reaction mixture has come to equilibrium,
what are the molar concentrations of Fe2+ and Fe3+?
A sample of ore containing the mineral tellurite (TeO2) was
dissolved in acid. The resulting solution was then reacted
with a solution of K2Cr2O7 to form telluric acid (H2TeO4). The
unbalanced chemical equation for the reaction.
_TeO2(s) + _Cr2O72- + _H+  _H2TeO4(aq) + _Cr3+ + _H2O
a. Identify the molecule or ion that is being oxidized.
b.
Give the oxidation number of Cr in the Cr2O72- ion.
c.
Balance the chemical equation given above.
5.
In the procedure described above, 46.00 mL of 0.03109 M
K2Cr2O7 was added to the ore sample after it was dissolved
in acid. When the chemical reaction had progressed as
completely as possible, the amount of unreacted (excess)
Cr2O72- was determined by titrating the solution with 0.110
M Fe(NO3)2. The reaction that occurred during the titration
is represented by the balanced equation:
6 Fe2+ + Cr2O72- + 14 H+  2 Cr3+ + 6 Fe3+ + 7 H2O
A volume of 9.85 mL of 0.110 M Fe(NO3)2 was required to
reach the equivalence point.
d. Calculate the moles of excess Cr2O72- titrated.
3.
e.
Calculate the moles of Cr2O72- that reacted.
f.
Calculate the mass of tellurite that was in the ore.
The mass of an aqueous solution of H2O2 is 6.951 g. The
H2O2 in the solution decomposes completely according to
the reaction represented below. The O2(g) produced is
collected in an inverted graduated tube over water at
23.4oC and has a volume of 182.4 mL when the water
levels inside and outside of the tube are the same. The
atmospheric pressure in the lab is 762.6 torr, and the
equilibrium vapor pressure of water at 23.4°C is 21.6 torr.
2 H2O2(aq) → 2 H2O(l) + O2(g)
a. Calculate the partial pressure of O2(g) in the tube.
b.
Calculate moles of O2(g) produced in the reaction.
c.
Calculate the mass of H2O2 that decomposed.
d.
Calculate the percent of H2O2 in the 6.951 g of solution.
6.
A(g) + B(g)  C(g) + D(g)
For the gas-phase reaction represented above, the
following experimental data were obtained.
Exp. Initial [A] Initial [B]
Initial Reaction Rate
(mol•L−1) (mol•L−1)
(mol•L−1•s-1)
1
0.033
0.034
6.67 x 10-4
2
0.034
0.137
1.08 x 10-2
3
0.136
0.136
1.07 x 10-2
4
0.202
0.233
?
a. Determine the order of the reaction with respect to
reactant A. Justify your answer.
b.
Determine the order of the reaction with respect to
reactant B. Justify your answer.
c.
Write the rate law for the overall reaction.
d.
Determine the value of the rate constant, k, for the
reaction. Include units with your answer.
e.
Calculate the initial reaction rate for experiment 4.
f.
The following mechanism has been proposed for the
reaction. Provide two reasons why the mechanism is
acceptable.
Step 1:
B + B  E + D slow
Step 2:
E+AB+C
fast equilibrium
g.
In the mechanism in part (f), is species E a catalyst, or
is it an intermediate? Justify your answer.
The reaction represented above is one that contributes
significantly to the formation of photochemical smog.
a. Calculate the quantity of heat released when 73.1 g of
NO(g) is converted to NO2(g).
b.
e.
Write the oxidation number of the oxygen atoms in
H2O2 and the oxidation number of the oxygen atoms in
O2 in the appropriate cells in the table below.
Substance
H2O2
O2
Oxidation Number of Oxygen Atoms
f. Write the balanced oxidation half-reaction.
4.
Methane gas reacts with chlorine gas to form dichloromethane and hydrogen chloride.
CH4(g) + 2 Cl2(g) → CH2Cl2(g) + 2 HCl(g)
a. A 25.0 g sample of methane gas is placed in a
reaction vessel containing 2.58 mol of Cl2(g).
(1) Identify the limiting reactant. Show calculations.
(2) Calculate the moles of CH2Cl2(g) after the limiting
reactant has been totally consumed.
The standard free-energy Go is -70.4 kJ at 25oC.
(1) Calculate the equilibrium constant Keq at 25°C.

(2) Indicate whether Go would become more
negative, less negative, or remain unchanged as
the temperature is increased. Justify your answer.

Calculate the standard molar entropy So for O2(g) at 25°C.
NO(g)
NO2 (g)
Substance
So (J•K-1•mol-1)
210.8
240.1
c.

Calculate the bond energy, in kJ•mol-1, of the nitrogenoxygen bond in NO2.
Bond Energy (kJ•mol-1)
Nitrogen-oxygen bond in NO
607
Oxygen-oxygen bond in O2
495
Nitrogen-oxygen bond in NO2
?
d.

AP Chemistry
Practice Units 10-12
Multiple Choice (No calculator)
Questions 1-3 refer to the chemical reactions represented below.
(A) HC2H3O2(aq) + NH3(aq)  C2H3O2- + NH4+
(B) Ba2+ + SO42-  BaSO4(s)
(C) Zn(OH)2(s) + 2 OH-  [Zn(OH)4]2(D) 2 K(s) + Br2(l)  2 KBr(s)
1. A precipitation reaction
2.
A reaction in which a coordination complex is formed
3.
A Lewis acid-base reaction that is not a Brønsted-Lowry
acid-base reaction
4.
The acid-dissociation constant, Ka, for a weak monoprotic
acid HA is 2.5 x 10-6. The pH of 0.40 M HA is closest to
(A) 2.0
(B) 3.0
(C) 4.0
(D) 6.0
5.
Which of the systems in equilibrium represented below will
exhibit a shift to the left (toward reactants) when the
pressure on the system is increased by reducing the
volume of the system? (Assume that the temperature is
constant.)
(A) 2 Mg(s) + O2(g)  2 MgO(s)
(B) SF4(g) + F2(g)  SF6(g)
(C) H2(g) + Br2(g)  2 HBr(g)
(D) SO2Cl2(g)  SO2(g) + Cl2(g)
6.
7.
8.
9.
Name _________________________
Period _____
10. At 25oC a saturated solution of a metal hydroxide, M(OH)2,
has a pH of 9.0. What is the value of the solubility-product
constant, Ksp, of M(OH)2(s) at 25oC?
(A) 1.0 x 10-27
(B) 5.0 x 10-19
(C) 5.0 x 10-16
(D) 1.0 x 10-15
11.
XY2(aq)  X2+ + 2 YA soluble compound XY2 dissociates in water according to
the equation above. In a 0.050 m solution of the compound,
the XY2(aq) species is 40.0 % dissociated. In the solution, the
number of moles of particles of solute per 1.0 kg of water is
closest to
(A) 0.15
(B) 0.090 (C) 1.040 (D) 0.020
12. Ascorbic acid, H2C6H6O6(s), is a diprotic acid with
K1 = 7.9 x 10-5 and K2 = 1.6 X 10-12. In a 0.005 M aqueous
solution of ascorbic acid, which of the following species is
present in the lowest concentration?
(A) H3O+
(B) H2C6H6O6
(C) HC6H6O6(D) C6H6O62-
Questions 13-14 The graph below shows the titration curve that
results when 100. mL of 0.0250 M acetic acid is titrated with
0.100 M NaOH.
In an aqueous solution with a pH of 11.50 at 25oC, the
molar concentration of OH-(aq) is approximately
(A) 3.2 x 10-12 M
(B) 3.2 x 10-3 M
(C) 2.5 x 10-1 M
(D) 2.5 M
Which of the following changes to a reaction system in
equilibrium would affect the value of the equilibrium
constant, Keq, for the reaction? (Assume in each case that
all other conditions are held constant.)
(A) Adding more of the reactants to the system
(B) Adding a catalyst for the reaction to the system
(C) Increasing the temperature of the system
(D) Increasing the pressure on the system
N2(g) + O2(g) + Cl2(g)  2 NOCl(g)
Ho = +104 kJ•mol-1
The equilibrium system represented above is contained in
a sealed, rigid vessel. Which of the following will increase
if the temperature of the mixture is raised?
(A) [N2]
(B) The rate of the forward reaction only
(C) The rate of the reverse reaction only
(D) The rate of both the forward and reverse reactions
F- + H2O  HF(aq) + OHWhich of the following species, if any, acts as a BrønstedLowry base in the reversible reaction represented above?
(A) HF(aq) (B) H2O
(C) F- only (D) F- and OH-
13. Which indicator is the best choice for this titration?
Indicator
pH Range of Color Change
(A) Methyl orange
3.2 - 4.4
(B) Methyl red
4.8 - 6.0
(C) Bromothymol blue
6.1 - 7.6
(D) Phenolphthalein
8.2 - 10.0
14. What part of the curve corresponds to the optimum buffer
action for the acetic acid/acetate ion pair?
(A) Point V
(B) Point X
(C) Point Z
(D) Along all of section YZ
15.
HCO3- + OH-  H2O(l) + CO32- H = -41.4 kJ
When the reaction represented by the equation above is at
equilibrium at 1 atm and 25°C, the ratio [CO32-]/[ HCO3-]
can be increased by doing which of the following?
(A) Decreasing the temperature
(B) Adding acid
(C) Adding a catalyst
(D) Diluting the solution with distilled water
1.
In another experiment 0.010 mol of pure isobutane is
placed in an evacuated 1.0 L rigid container and allowed to
come to equilibrium at 25°C.
d. What are the molar concentration of each species
after equilibrium has been established? Justify your
answer.
Free Response (Calculator)
Answer the following questions about the solubility of the
salts Li3PO4 and PbCl2. Assume that hydrolysis effects are
negligible. The equation for the dissolution of Li3PO4(s) is
Li3PO4(s)  3 Li+ + PO43Ksp = 3.2 x 10-9
a. Write the equilibrium-constant expression for the
dissolution of Li3PO4(s).
3.
b.
Assuming that volume changes are negligible, calculate
the maximum number of moles of Li3PO4(s) that can
dissolve in
(1) 0.50 L of water
The aqueous ethylamine reacts with water according to the
equation: C2H5NH2(aq) + H2O  C2H5NH3+ + OHb. Write the equilibrium-constant expression for the
reaction between C2H5NH2(aq) and water.
(2) 0.50 L of 0.20 M LiNO3
The equation for the dissolution of PbCl2, is
2+ + 2 ClPbCl2
Ksp = 1.6 x 10-5
c. Calculate the concentration of Cl- in a saturated
solution of PbCl2.
d.
2.
A pure 14.85 g sample of the weak base ethylamine,
C2H5NH2, is dissolved in enough distilled water to make
500. mL of solution.
a. Calculate the molar concentration of the C2H5NH2 in
the solution.
An open container holds 1.000 L of 0.00400 M PbCl2,
which is unsaturated. Calculate the minimum volume of
water, in mL, that must evaporate from the container
before solid PbCl2 can precipitate.
c.
Which is present in the solution at the higher
concentration at equilibrium, C2H5NH2(aq) or
C2H5NH3+? Justify your answer.
d.
A different solution is made by mixing 500. mL of
0.500 M C2H5NH2 with 500. mL of 0.200 M HCl. The
pH of the resulting solution is found to be 10.93.
(1) Calculate the concentration of OH- in the solution.
(2) Write the net-ionic equation that represents the
reaction that occurs when the C2H5NH2 solution is
mixed with the HCl solution.
Butane, C4H10, occurs in two isomeric forms, n-butane and
isobutane. Both exist as gases at 25°C and 1.0 atm. The
two isomers exist in equilibrium by the equation:
n-butane(g)  isobutane(g)
Kc = 2.5 at 25°C
A 0.010 mol sample of pure n-butane is placed in an
evacuated 1.0 L rigid container at 25°C.
a. Write the expression for the equilibrium constant Kc.
(3) Calculate the molar concentration of the
C2H5NH3+ that is formed in the reaction.
(4) Calculate the value of Kb for C2H5NH2.
b.
Calculate the initial pressure in the container when the
n-butane is first introduced (before the reaction starts).
4.
c.
The n-butane reacts until equilibrium has been
established at 25°C.
(1) What is the total pressure at equilibrium? Justify
your answer.
(2) Calculate the molar concentration of each species
at equilibrium.
(3) The volume of the system is reduced to 0.50 L,
what is the new concentration of n-butane after
equilibrium has been reestablished at 25°C?
Justify your answer.
Answer the questions that relate to halogen oxyacids.
a. Use the information in the table to answer part a(1).
Ka at 298 K
Acid
HOCl
2.9 x 10-8
HOBr
2.4 x 10-9
(1) Which of the two acids is stronger, HOCl or
HOBr? Justify your answer in terms of Ka.
(2) Draw a complete Lewis electron-dot diagram for
the stronger acid.
(3) Hypoiodous acid has the formula HOI. Predict
whether HOI is a stronger acid or a weaker acid
than the acid that you identified in part a(1).
Justify your answer in terms of chemical bonding.
b.
Write the equation for the reaction that occurs
between hypochlorous acid and water.
c.
A 1.2 M NaOCl solution is prepared by dissolving solid
NaOCl in distilled water at 298 K according to the
reaction: OCl– + H2O  HOCl(aq) + OH−
(1) Write the equilibrium-constant expression for the
hydrolysis reaction between OCl- and H2O.
6.
Answer the questions that relate to salts of lead and barium.
a. A saturated solution is prepared by adding excess
PbI2(s) to distilled water to form 1.0 L of solution at
25°C. The concentration of Pb2+ in the saturated
solution is found to be 1.3 x 10-3 M. The equation is:
PbI2(s)  Pb2+ + 2 I(1) Write the equilibrium expression for the equation.
(2) Calculate the molar concentration of I-.
(2) Calculate the value of the equilibrium constant at
298 K for the hydrolysis reaction.
d.
(3) Calculate the equilibrium constant Ksp.
(3) Calculate the value of [OH-] in the 1.2 M NaOCl
solution at 298 K.
b.
A saturated solution is prepared by adding PbI2(s) to
distilled water to form 2.0 L of solution at 25°C. What
are the molar concentrations of Pb2+ and I-? Justify
your answer.
A buffer solution is prepared by dissolving some solid
NaOCl in a solution of HOCl at 298 K. The pH of the
buffer solution is determined to be 6.48.
(1) Calculate the [H3O+] in the buffer solution.
c.
Solid NaI is added to a saturated solution of PbI2 at
25°C. Assuming that the volume of the solution does
not change, does the molar concentration of Pb2+ in
the solution increase, decrease, or remain the same?
Justify your answer.
d.
The value of Ksp for the salt BaCrO4 is 1.2 x 10-10.
When a 500. mL sample of 8.2 x 10-6 M Ba(NO3)2 is
added to 500. mL of 8.2 x 10-6 M Na2CrO4, no
precipitate is observed.
(1) Assuming that volumes are additive, calculate the
molar concentrations of Ba2+ and CrO42- in the
1.00 L of solution.
(2) Indicate which of HOCl(aq) or OCl− is present at
the higher concentration in the buffer solution.
Support your answer with a calculation.
5.
Hydrofluoric acid, HF(aq), dissociates in water as
represented by the equation:
HF(aq)  H+ + FKa = 7.2 x 10-4
a. Write the equilibrium-constant expression for the
dissociation of HF(aq) in water.
b.
Calculate the molar concentration of H3O+ in a 0.40 M
HF(aq) solution.
HF(aq) reacts with NaOH(aq) according to the reaction.
HF(aq) + OH-  H2O + FA volume of 15 mL of 0.40 M NaOH(aq) is added to 25 mL
of 0.40 M HF(aq) solution.
c. Calculate the moles of HF(aq) remaining in the solution.
d.
Calculate the molar concentration of F- in the solution.
e.
Calculate the pH of the solution
(2) Use the molar concentrations of Ba2+ ions and
CrO42- ions as determined above to show why a
precipitate does not form. You must include a
calculation as part of your answer.