2022 Tests and Keys
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School
University of Ottawa *
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Course
1311 -
Subject
Chemistry
Date
Jan 9, 2024
Type
Pages
57
Uploaded by MinisterWillpowerMeerkat40
CHM1311 E FALL 2022
Page 1 of 2
IN-CLASS PRACTICE QUIZ
Name: _______________________________________
TIME ALLOTTED = 30 min
Student Number: _____________________________
1.
(1.5 pts) Complete the following table:
2.
(1 pt) The number of ions present in 250 mL of 0.00100 M CaCl
2
(
aq
) is:
4.52 x 10
20
2.50 x 10
-4
6.02 x 10
23
1.51 x 10
20
3.
(1 pt) Toothpaste contains 0.21% m/v sodium fluoride. This concentration expressed in mol/L
is: ___________________________________________.
4.
(0.5 pt) The empirical formula for a new fuel is determined by combustion analysis to be
C
3
H
4
O. The molecular mass of the fuel is found by mass spectrometry to be 168.2 u. The
molecular formula of the fuel is: __________________________________.
5.
(4 pts) Copper has two naturally occurring isotopes,
63
Cu (isotopic mass = 62.9396 u) and
65
Cu
(64.9278 u). If copper has an average atomic mass of 63.546 u, what is the percent abundance of
each isotope?
%abundance of
63
Cu = ___________________
%abundance of
65
Cu = ___________________
Element
Mass Number
Number of
protons
Number of
electrons
Number of
neutrons
Charge
Sr
89
+2
CHM1311 E FALL 2022
Page 2 of 2
6.
In an environmental test for dissolved iodide ion in saltwater, the iodide undergoes redox
chemistry in acidic solution, according to the following half-reactions:
I
–
(aq)
à
I
2
(s)
NO
3
–
(aq)
à
N
2
(g)
a)
(4 pts) Derive a balanced redox reaction, including phases. Underline the reducing agent.
b)
(3 pts) A 50.0 mL sample of seawater was found to react with 1.867 mL of a 0.0520 M
Ca(NO
3
)
2
solution. What was the molarity of iodide ion in the seawater sample?
TOTAL SCORE = ________ / 15
CHM1311 Midterm 1 2022
Page 1 of 8
LAST NAME: __________________________________________________________
FIRST NAME:
_________________________________________________________
Student Number: ______________________________________________________
CHM 1311 E
Midterm #1
Fall 2022
Please keep your work covered at all times and keep your eyes on your own paper!
Cheating or any appearance of cheating will result in an F in the course and possible
expulsion from the university.
There are 6 pages in this test.
A periodic table, data tables, and a formula sheet are
provided at the end – you may GENTLY remove these pages and use them as scrap
paper. Non-programmable calculators are permitted. Please show your work where
appropriate to receive full credit.
Cellular phones, unauthorized electronic devices, and any other materials are not
allowed during this exam.
Phones and devices must be turned off and put away in your
bag.
Do not keep them in your possession, such as in your pockets.
If caught with such
a device or document, academic fraud allegations may be filed which may result in you
obtaining a 0 (zero) for the exam.
By signing below, you acknowledge that you have ensured that you are complying with
the above statement.
Signature: _____________________________________
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CHM1311 Midterm 1 2022
Page 3 of 8
1. Short Answer Questions
a)
(1 pt) Four different compounds have the specific heat capacities shown below. If 100 g
of each compound, all starting at 20.0ºC, absorb 450 J of heat, which compound will have
the highest final temperature?
A
B
C
D
15 J/gºC
0.15 J/gºC
43 J/gºC
27 J/gºC
b)
(1 pt) A solution of NH
3
and H
2
O is 45% H
2
O
by mass
; NH
3
is the solvent.
True
False
c)
(1 pt) If the molar mass of a gas is
doubled
, the root-mean-squared
speed of the molecules will increase by a factor of:
d)
(1 pt) You take a 4.0 L volume of gas at 200 K. You expand the gas to an 8.0 L volume and
simultaneously heat the vessel to 800 K. The pressure of the gas:
DOUBLES
HALVES
QUADRUPLES
STAYS CONSTANT
e)
(2 pts) Among the following, circle the compound with the highest oxidation state of
nitrogen and underline the compound with the lowest oxidation state of nitrogen.
NO
+
N
2
NO
3
–
NO
2
N
2
O
NH
3
f)
(2 pts) Starting with an atom of germanium-72, we add 3 protons, add 6 neutrons, and
add 4 electrons to the atom. Fill in the blanks for our new species:
Number of protons
Number of neutrons
Number of electrons
Chemical Symbol
g)
(1 pt) The percent yield for two successive reactions, A
à
B and B
à
C,
are 45% and 79%, respectively. The overall percent yield for the
conversion of A to C is:
h)
(1 pt) The energy change shown in the diagram at right corresponds to an:
c
EXOTHERMIC CONTRACTION
c
ENDOTHERMIC CONTRACTION
c
EXOTHERMIC EXPANSION
c
ENDOTHERMIC EXPANSION
BONUS - For the hypothetical reaction below, carried out under constant pressure
conditions, which of the following are correct? Circle all that apply.
∆
V > 0
W > 0
∆
U = q + W
∆
V < 0
W < 0
∆
U > 0
∆
V = 0
W = 0
∆
U < 0
Energy
U
1
U
2
q
W
A (
g
) + 2 B (
l
)
à
3 C (
g
) + heat
CHM1311 Midterm 1 2022
Page 4 of 8
2. Barium sulfate is used as a radiocontrast agent for X-ray imaging of the digestive system.
A patient is given a beaker filled with a solution that contains 0.250% BaSO
4
by mass. The
density of the imaging solution is 1.45 g/mL.
a)
(3 pts) What is the molarity of the solution?
b)
(3 pts) What is the molality of the solution?
c)
(4 pts) The cylindrical beaker has a diameter of 8.00 cm and a height of 15.0 cm. Given
that the percent natural abundance of
134
Ba is 2.417%, how many
134
Ba atoms will be
ingested by the patient?
Recall:
volume of a cylinder =
p
r
2
h
CHM1311 Midterm 1 2022
Page 5 of 8
3. A 3.902 g sample of an unknown compound containing only C, H, and O is combusted in
an oxygen-rich environment.
a)
(3 pts) The CO
2
gas produced in the reaction is collected over water at 20.00ºC in a 5.000
L flask. The pressure in the flask is measured to be 100.52 kPa. What is the number of
moles of carbon dioxide gas produced in the combustion? The vapour pressure of water
at 20.00ºC is 2.3393 kPa.
b)
(5 pts) The reaction was found to also produce 3.633 g of liquid H
2
O. What is the empirical
formula of the unknown compound?
c)
(2 pts) If the molecular mass of the unknown compound is found to be 116.2 u, what is
its molecular formula?
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CHM1311 Midterm 1 2022
Page 6 of 8
4. In a constant-pressure calorimeter, 65.0 mL of 0.0800 M aqueous sulfuric acid was added
to 65.0 mL of 0.250 M aqueous sodium hydroxide. The reaction caused the temperature of
the solution to rise from 23.60°C to 25.10°C.
a)
(1 pt) This acid-base neutralization forms aqueous sodium sulfate and liquid water.
Write a balanced molecular equation (including phases) for the reaction.
b)
(4 pts) If the solution has the same density and specific heat capacity as water, what is
Δ
H for this reaction, in kJ per mole of H
2
O produced? You may assume that the final total
volume of the solution is equal to the sum of the individual volumes.
CHM1311 Midterm 1 2022
Page 7 of 8
5. Methane (CH
4
) and chlorine gas react at high temperature to form chloromethane (CH
3
Cl)
and hydrogen chloride.
a)
(4 pts) If this reaction has a 75.0% yield, what mass (in g) of chloromethane will form
when 20.5 g of methane and 45.0 g of chlorine gas are reacted together?
b)
(2 pts) When carried out under constant pressure conditions entirely in the gas phase at
450 K, the above reaction absorbs 788 J of heat. Determine
∆
U for the reaction, in kJ/mol.
c)
(1 pt) On the following template, draw a representative energy
diagram for the reaction, labelling U
1
, U
2
,
∆
U, q and W.
Energy
CHM1311 Midterm 1 2022
Page 8 of 8
6. Dr. Fox decides to demonstrate Boyle’s law while scuba diving. She takes a syringe filled
with 18.0 mL of air from the surface (which is at an atmospheric pressure of 1.014 bar and a
temperature of 25.95ºC) with her on a dive to a depth of 12 m.
a)
(3 pts) During the dive, the volume of the air in the syringe drops to 5.40 mL and the
temperature drops to 23.12ºC. What is the pressure in the syringe at this depth, in bars?
b)
(1 pt) Under which condition do the gas molecules in
the syringe have the greater average kinetic energy?
c)
(1 pt) The air sample contains nitrogen and oxygen
gases. Which gas has the greatest root-mean-squared
speed?
d)
(3 pts) If the mole fraction of oxygen in air is 0.209, calculate the number of moles of
oxygen in the syringe.
c
AT THE SURFACE (at 0 m)
c
UNDERWATER (at 12 m)
c
N
2
at 0 m
c
N
2
at 12 m
c
O
2
at 0 m
c
O
2
at 12 m
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CHM1311 – Midterm 2 – 2022
Page 1 of 9
LAST NAME: __________________________________________________________
FIRST NAME:
_________________________________________________________
Student Number: ______________________________________________________
CHM 1311 E
Midterm #2
Fall 2022
Please keep your work covered at all times and keep your eyes on your own paper!
Cheating or any appearance of cheating will result in an F in the course and possible
expulsion from the university.
A periodic table, data tables, and a formula sheet are provided at the end of this test –
you may GENTLY remove these pages and use them as scrap paper. Non-
programmable calculators are permitted. Please show your work where appropriate
to receive full credit. You have 90 min to complete the midterm.
Cellular phones, unauthorized electronic devices, and any other materials are not
allowed during this exam.
Phones and devices must be turned off and put away in your
bag.
Do not keep them in your possession, such as in your pockets.
If caught with such
a device or document, academic fraud allegations may be filed which may result in you
obtaining a 0 (zero) for the exam.
By signing below, you acknowledge that you have ensured that you are complying with
the above statement.
Signature: _____________________________________
CHM1311 – Midterm 2 – 2022
Page 3 of 9
1.
(10 pts) Short Answer Questions
a)
(2 pts) In the reaction: N
2
O
4
(g)
D
2 NO
2
(g) (
∆
H = 57.2 kJ/mol), the reactant is a colourless
gas and the product is a brown gas. A flask contains a mixture of these gases at
equilibrium. In the box, write the equilibrium constant and choose the best means which
would lead to an increase in the observed colour.
£
remove NO
2
and remove heat
£
add NO
2
and decrease volume
£
remove N
2
O
4
and add heat
£
add N
2
O
4
and increase volume
b)
(1 pt) The standard heat of formation of solid ammonium chloride is –314 kJ. Write the
chemical equation for the reaction to which this value applies.
c)
(1 pt) The conjugate acid and conjugate base of HPO
4
–
are ___________________________
and ___________________________
respectively.
d)
(1 pt) Which of the following would be the correct van’t Hoff plot for an endothermic
reaction?
e)
(0.5 pt) Which of the following ions is the weakest base?
N
3
-
NO
2
-
F
-
HO
2
-
f)
(1 pt) Circle the two ‘ingredients’ you would use to prepare a buffer of pH = 9.05.
CH
3
COOH
HOCl
NaOH
HCN
CH
3
COONa
NaCl
HCl
KCN
lnK
1/T
A
B
C
D
lnK
1/T
lnK
1/T
lnK
1/T
K =
CHM1311 – Midterm 2 – 2022
Page 4 of 9
g)
(2 pts) In the following list, circle the acidic salt(s) and underline the basic salt(s).
LiCl
NaF
NH
4
Br
TiCl
4
KNO
3
NaN
3
h)
(0.5 pt) Bond breaking is always an endothermic process.
TRUE
FALSE
i)
(0.5 pt) A chemical equilibrium can be considered to be “going to completion” when
the value of K is at least
10
–10
10
–5
10
10
5
or
greater.
j)
(0.5 pt) A buffer made from HA (pK
a
= 4.82) and NaA has a pH of 4.75. The buffer
therefore contains:
[HA] > [A
–
]
[HA] < [A
–
]
[HA] = [A
–
]
BONUS
Give the expected products of the following acid-base reaction, label the acid, base,
conjugate acid, and conjugate base, and determine the preferred direction of the
equilibrium.
Cl
–
+
HNO
2
D
K > 1
K < 1
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CHM1311 – Midterm 2 – 2022
Page 5 of 9
2.
The following reaction takes place entirely in the gas phase at 550 K:
a)
(3 pts) Using the table of bond energies, estimate the energy change of the reaction. Show
your work to receive all points.
b)
(3 pts) Using the table of
∆
H
f
º values, determine the enthalpy change of the reaction.
Show your work to receive all points.
c)
(1 pt) Which of the following energy diagrams best represents the reaction?
A
B
C
D
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
C
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
+
+
ENERGY
U
1
U
2
q
ENERGY
U
1
U
2
q
ENERGY
U
2
U
1
q
ENERGY
U
2
U
1
q
Bond
Energy (kJ/mol)
C–C
348
C=C
612
H–H
436
C–H
413
Compound
∆
H
f
º (kJ/mol)
C
6
H
5
CH
3
(
l
)
12.0
C
6
H
5
CH
3
(
g
)
50.1
C
6
H
6
(
l
)
49.0
C
6
H
6
(
g
)
82.9
CH
4
(
g
)
–74.8
CHM1311 – Midterm 2 – 2022
Page 6 of 9
3.
An engineer who is examining the oxidation of SO
2
in the manufacture of sulfuric acid
determines that K
c
= 1.7x10
8
at 600. K :
2 SO
2
(
g
) + O
2
(
g
)
D
2 SO
3
(
g
)
a)
(2 pts) What is the value of K
P
?
b)
(2 pts) At equilibrium, P
SO3
= 300. bar and P
O2
= 100. bar. Calculate P
SO2
, in bars.
c)
(1 pt) In another experiment, the engineer places a mixture of 0.0040 mol of SO
2
, 0.0028
mol of O
2
and 0.0034 mol of SO
3
in a 1.00 L flask at 600. K. In which direction will the
reaction proceed?
TOWARDS REACTANTS
TOWARDS PRODUCTS
ALREADY AT EQUILIBRIUM
d)
(3 pts) In the second step of the process, the sulfur trioxide is converted to sulfuric acid:
SO
3
(
g
) + H
2
O(
g
)
D
H
2
SO
4
(
g
)
K
c
= 3.4x10
3
at 600. K
Given this information, determine K
c
for the overall conversion of SO
3
to H
2
SO
4
:
2 SO
2
(
g
) + O
2
(
g
) + 2 H
2
O(
g
)
D
2 H
2
SO
4
(
g
)
K
c
= ? at 600. K
CHM1311 – Midterm 2 – 2022
Page 7 of 9
4.
Two FBI agents, Mulder and Scully, are investigating a series of strange murders. In each
case, the victim was found suspended in a solution of ammonium benzoate, NH
4
C
7
H
5
O
2
.
a)
(4 pts) Will these salt solutions be acidic, basic, or neutral? Show your reasoning to earn
full points. (K
b
of ammonia is 1.8 x 10
–5
).
b)
(6 pts) Agent Scully determines that the solution concentration is 0.128 M. What is the
exact pH of the solution?
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CHM1311 – Midterm 2 – 2022
Page 8 of 9
5.
A buffer that contains 0.220 M HA and 0.297 M A
–
has a pH of 3.87.
a)
(4 pts) What is the pK
a
of the buffer?
b)
(6 pts) What is the change in pH after 0.0015 mol of Ba(OH)
2
is added to 0.500 L of this
buffer solution? Ba(OH)
2
dissolves completely; the Ba
2+
(
aq
) ion has no acid-base
character.
BONUS – What are HA and A
–
? (Give their formulas). Show your reasoning.
CHM1311 – Midterm 2 – 2022
Page 9 of 9
6.
(5 pts) After a vacation of scuba-diving, Dr. Fox has to clean and rinse all her scuba gear
before putting it back into storage. She wants to use “
Diver’s Buddy Scuba Shampoo
”, a
commercially available aqueous solution of trimethylamine (N(CH
3
)
3
, K
b
= 6.31 x 10
–6
).
Dr. Fox measures the pH of the solution and finds it to be 10.05. What is the concentration
of trimethylamine in the shampoo, in mol/L?
CHM1311 E – Final Exam 2022
Page 1 of 14
LAST name (IN CAPITAL LETTERS): _______________________________________________
FIRST name:
_____________________________________________________________________
Student Number: _________________________________________________________________
Seat Number: ___________
CHM 1311 E
Final Exam
December 2022
Attention: If you didn’t have
Dr. Focsaneanu (Fox)
as your Instructor, you
shouldn’t be writing this exam!
INSTRUCTIONS:
•
This is a closed book exam with no notes allowed.
•
Non-graphing, non-programmable calculators are allowed.
•
Please show all work to receive partial credit.
•
A periodic table, data tables, and a formula sheet are provided at the end.
You
may gently remove these pages off the exam and use them to cover your work.
There are 14 pages in this exam (+ 4 data sheets). You have 3h to complete the exam.
Cellular phones, unauthorized electronic devices or course notes are not allowed
during this exam.
Phones and devices must be turned off and put away in your bag.
Do
not keep them in your possession, such as in your pockets. If caught with such a device
or document, academic fraud allegations may be filed which may result in you obtaining
a 0 (zero) for the exam.
By signing below, you acknowledge that you have ensured that you are complying with
the above statement.
Signature: _____________________________________
Please INITIAL HERE when you
have verified that there are 14
pages in your exam copy:
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CHM1311 E – Final Exam 2022
Page 3 of 14
1.
Short Answer Questions.
a)
(0.5 pt) Which of the following isotopes has the greatest number of neutrons?
b)
(1 pt) An aqueous solution of sulphuric acid has a concentration of 2.45 mol/kg.
The
mole fraction of H
2
SO
4
in this mixture is : _______________________________
c)
(2 pts) The contents of two test tubes, containing AgNO
3
(
aq
) and CaCl
2
(
aq
), are mixed
together. Write the balanced molecular equation for the expected precipitation (if any)
including phases:
d)
(0.5 pt) 1.0 mol of an ideal gas is placed in a 1.0 L flask at 22ºC. Which of the following
would result in the greatest increase in the pressure of the gas?
£
reducing the volume of the container to 0.50 L
£
increasing the amount of gas to 1.5 mol
£
increasing the temperature to 300ºC
e)
(0.5 pt) Below is a hypothetical configuration for the ground state of a scandium atom.
This configuration is incorrect because:
1s
2
2s
2
2p
6
3s
2
3p
6
3d
1
4s
2
£
it contains one or more orbitals that do not exist
£
it contains too few electrons
£
it contains too many electrons
£
it contains electrons in incorrect orbitals
£
it contains orbitals listed in incorrect order
f)
(0.5 pt) A student draws the orbital energy diagram at right for a carbon atom. As shown,
this diagram:
£
is correct
£
disobeys the Pauli Exclusion Principle
£
disobeys Hund’s Rule
£
disobeys the Aufbau Principle
17
35
Cl
19
40
K
17
37
Cl
20
40
Ca
E
1s
2s
2p
CHM1311 E – Final Exam 2022
Page 4 of 14
g)
(1 pt) The number of atoms in 10.0 g of CaCO
3
(100.0 g/mol) is:
1.81 x 10
23
6.02 x 10
22
3.01 x 10
23
1.21 x 10
23
h)
(0.5 pt) For the orbital shown on the 3D axes provided at right, a possible
set of quantum numbers would be n = 3,
l
= _______ , m
l
= – 2.
i)
(1 pt) Given the information below, the value of the equilibrium constant for the reaction
A(g)
+
B(g)
D
2C(g)
is = __________________________.
2A(g)
D
2X(g)
K
P
= 35.5
2C(g)
D
X(g)
+
B(g)
K
P
= 7.2
j)
(1 pt) The standard heat of formation of solid ammonium chloride is –314 kJ. Write the
chemical equation for the reaction to which this value applies (including phases).
k)
(1 pt) For the compounds listed below, how many will be
more
soluble in a pH = 4.5
buffer than in pure water?
NONE
1
2
3
ALL OF THEM
PbI
2
CaCO
3
BaF
2
Zn(OH)
2
l)
(2 pts) For a first order reaction, the half-life
______________________
with increasing
reactant
concentration.
For
a
second
order
reaction,
the
half-life
__________________________ with increasing reactant concentration.
m)
(1 pt) A one litre balloon is filled with neon gas. A hole is made in the balloon and the
gas effuses at a rate of 0.0280 mol/hr. If the same balloon is refilled with argon at the
same pressure and temperature, its rate of effusion would be _______________________.
n)
(0.5 pt) It is possible to prepare a buffer by taking a strong base and titrating it with a
strong acid to the half equivalence point.
TRUE
FALSE
x
y
z
CHM1311 E – Final Exam 2022
Page 5 of 14
o)
(1 pt) The figure on the left shows 1
mol
of
gas
in
an
open-end
manometer. The external pressure is
1.0 bar and the temperature is 300K.
In the box, sketch the manometer
and qualitatively show the effect on
the gas if the external pressure
increases
to
2.0
bar
and
the
temperature of the gas is increased
to 600K.
p)
(1 pt) Solid potassium chromate is slowly added to an aqueous solution that contains
0.200 M each Pb
2+
and Ag
+
ions. The compound that precipitates first is:
___________________________.
q)
(1 pt) For an ideal gas, a graph of PV versus T will be a linear relationship with a slope
that is directly proportional to the gas’s:
KINETIC ENERGY
MOLAR MASS
ENTHALPY
MASS
r)
(2 pts) For the hypothetical reaction below, carried out under constant pressure
conditions, which of the following are correct? Circle all that apply.
∆
V > 0
W > 0
∆
U = q + W
∆
V < 0
W < 0
∆
U > 0
∆
V = 0
W = 0
∆
U < 0
s)
(1 pt) Name two ways to accelerate a chemical reaction.
A (
g
) + 2 B (
l
)
à
3 C (
g
) + heat
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CHM1311 E – Final Exam 2022
Page 6 of 14
t)
(1 pt) The graph at right represents the concentrations as a function of time for the
reaction A(g)
D
B(g). Which of the following statements is/are true? Select all that apply.
c
K
P
is equal to 1
c
K
P
is greater than 1
c
K
P
is less than 1
c
K
P
is equal to K
C
c
The system never reaches equilibrium
BONUS 1
Sulfurous acid (H
2
SO
3
) has pK
a1
= 1.85 and pKa
2
= 7.20. An aqueous solution of this acid is
titrated with NaOH (aq). At the
second
equivalence point, the pH of the solution will be
ACIDIC
BASIC
NEUTRAL
Write the chemical equation for the expected hydrolysis (no phases necessary):
BONUS 2
Most of the students registered in this course aren’t studying chemistry, but this course is
mandatory for so many programs because it covers a lot of fundamental science required for
other disciplines and it also trains you in problem-solving. Describe an occasion where you
were able to apply a concept from CHM1311 elsewhere (in another course, in your daily life,
etc
.). If you can’t think of an example, then describe a favourite fact or concept you learned
this term in CHM1311.
Concentration
Time
A
B
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CHM1311 E – Final Exam 2022
Page 7 of 14
2.
You wish to prepare a buffer solution with pH = 9.45.
a)
(5 pts) How many grams of (NH
4
)
2
SO
4
would you add to 425 mL of 0.258 M NH
3
to do
this? You may assume that the solution’s volume remains constant. K
b
of NH
3
= 1.8x10
-5
Answer: ________________________________
b)
(5 pts) You have access to additional 0.258 M NH
3
and more solid (NH
4
)
2
SO
4
. Which
buffer component, and how much (in g or mL) would you add to 0.100 L of the buffer in
part (a) to change its pH to 9.30? You may assume that the solution’s volume remains
constant.
Component: _________________________
Amount: _________________________
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CHM1311 E – Final Exam 2022
Page 8 of 14
3.
Peroxyacetyl nitrate (PAN) is an air pollutant
produced during photochemical smog events.
PAN is unstable and dissociates as shown at right.
a)
(3 pts) Using the data in the table below, derive a rate law for the decomposition of PAN
at 25.0ºC, as well as the value of the rate constant (with appropriate units).
Trial
Initial [PAN]
(M)
Initial Rate
(M/min)
1
8.30x10
–10
1.92x10
–11
2
1.66x10
–9
3.84x10
–11
3
2.49x10
–9
5.78x10
–11
Rate law is:
___________________________
Rate constant is:
___________________________
b)
(2 pts) The decomposition of PAN has a half-life of 35.0 hr at 0.00ºC. What is the rate
constant for this reaction at this temperature? Use the same units as part (a).
c)
(3 pts) What is the activation energy, in kJ/mol, for this reaction?
Activation energy : _______________________
d)
(2 pts) The enthalpy for the decomposition of
PAN is about 88 kJ/mol. On the axes provided,
draw a representative reaction profile for this
reaction,
with labels
.
reaction coordinate
Energy
CH
3
COONO
2
CH
3
COO
+
NO
2
O
O
PAN
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CHM1311 E – Final Exam 2022
Page 9 of 14
4.
Electrons in Atoms.
a)
(3 pts) For the following sets of quantum numbers, give the subshell label, the allowed
values of
m
l
and the number of orbitals in the subshell (the first row is an example).
n
and
l
subshell label
m
l
values
number of orbitals
n
= 1 and
l
= 0
1
s
0
1
n
= 3
and
l
= 1
n
= 5 and
l
= 2
b)
(3 pts) How many electrons can be described by each of the following sets of quantum
numbers?
i.
n
= 4,
l
= 2,
m
l
= 3
ii.
n
= 3,
l
= 2,
m
l
= -1,
m
s
= –
½
iii.
n
= 4,
l
= 3
c)
(4 pts) Draw a diagram of Bohr’s model of the hydrogen atom showing the transition of
an electron from the
n
= 5 level to the ground state. What is the change in energy (in
kJ/mol) of this transition?
Answer: _______________________________
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CHM1311 E – Final Exam 2022
Page 10 of 14
5.
A 125 g stainless steel ball (c = 0.50 J/gºC) at 525ºC is dropped into 75.0 mL of water at
28.5ºC in an open Styrofoam cup. You observe the release of some steam.
a)
(7 pts) Using values from the data sheets, calculate the mass (in g) of the steam that
escaped.
Mass of steam: ________________________________
b)
(3 pts) A second identically-sized ball, made from a metal with a higher specific heat
capacity than stainless steel, is subjected to the same conditions as part (a). Do you expect
the mass of produced steam to be greater or smaller? Explain.
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CHM1311 E – Final Exam 2022
Page 11 of 14
6.
Dr. Fox decides to demonstrate Boyle’s law while scuba diving. She takes a syringe filled
with 18.0 mL of air from the surface (which is at an atmospheric pressure of 1.014 bar and
a temperature of 25.95ºC) with her on a dive to a depth of 12 m.
a)
(3 pts) During the dive, the volume of the air in the syringe drops to 5.40 mL and the
temperature drops to 23.12ºC. What is the pressure in the syringe at this depth, in bars?
b)
(1 pt) Under which condition do the gas molecules in
the syringe have the greater average kinetic energy?
c)
(3 pts) If the mole fraction of oxygen in air is 0.209, calculate the number of moles of
oxygen in the syringe.
d)
(3 pts) Match the three gases shown
with the expected molecular speed
distribution diagrams (A, B, C) at
right.
c
AT THE SURFACE (at 0 m)
c
UNDERWATER (at 12 m)
NUMBER OF MOLECULES
ROOT-MEAN-SQUARED SPEED
A
B
C
______
N
2
at 0 m
______
O
2
at 12 m
______
N
2
at 12 m
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CHM1311 E – Final Exam 2022
Page 12 of 14
7.
You are performing a titration of
100.0 mL of 0.110 M HC
7
H
5
O
2
with 0.110 M NaOH. Determine
the pH of the solution:
a)
(3 pts) initially
b)
(2 pts) at the half-equivalence
point
c)
(4 pts) at the equivalence point
d)
(1 pt) Use these values to sketch
a titration curve on the graph
provided.
0
2
4
6
8
10
12
14
0
20
40
60
80
100
120
140
pH
mL OH
–
added
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CHM1311 E – Final Exam 2022
Page 13 of 14
8.
Barium sulfate is used in medical imaging of the gastrointestinal tract because it is
opaque to X rays. A barium sulfate solution is ingested by the patient, whose stomach
and intestines can then be visualized via X-ray imaging.
a)
(5 pts) If a patient ingests 200 mL of a saturated barium sulfate solution, how many toxic
Ba
2+
ions has the patient consumed?
Answer: ________________________________
b)
(3 pts) There are some data that suggest that zinc lozenges can significantly shorten the
duration of a cold. If the solubility of zinc acetate, Zn(CH
3
COO)
2
, is 43.0 g/L, what is the
K
sp
of this compound?
Answer: ________________________________
c)
(2 pts) How might one use pH to improve the solubility of zinc acetate? Explain, using
Le Chatelier’s Principle.
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CHM1311 E – Final Exam 2022
Page 14 of 14
9.
Chlorine gas can be generated by the following redox process:
a)
(3 pts) Find the overall balanced redox reaction, under acidic conditions.
b)
(4 pts) 10.0 g of KMnO
4
is dissolved in 250.0 g of an aqueous solution of NaCl that is 5.2%
NaCl by mass. What is the expected amount, in moles, of chlorine gas produced in the
reaction?
Answer: __________________________________
c)
(3 pts) The chlorine gas produced in part (b) is collected over water at 26.0ºC, at a total
gas pressure of 0.9840 bar. If 1.37 L of gas is obtained, what is the percent yield of the
reaction in part (b)? The vapour pressure of water at 26.0ºC is 3.3639 kPa.
Answer: ________________________________
MnO
4
–
(
s
)
à
Mn
2+
(
aq
)
Cl
–
(
aq
)
à
Cl
2
(
g
)
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CHM1311 E FALL 2022
Page 1 of 2
IN-CLASS PRACTICE QUIZ
Name: _______________________________________
TIME ALLOTTED = 30 min
Student Number: _____________________________
1.
(1.5 pts) Complete the following table:
2.
(1 pt) The number of
ions
present in 250 mL of 0.00100 M CaCl
2
(
aq
) is:
4.52 x 10
20
2.50 x 10
-4
6.02 x 10
23
1.51 x 10
20
3.
(1 pt) Toothpaste contains 0.21% m/v sodium fluoride. This concentration expressed in mol/L
is: ____
0.050 mol/L
_________________________.
4.
(0.5 pt) The empirical formula for a new fuel is determined by combustion analysis to be
C
3
H
4
O. The molecular mass of the fuel is found by mass spectrometry to be 168.2 u. The
molecular formula of the fuel is: __
C
9
H
12
O
3
____________________.
5.
(4 pts) Copper has two naturally occurring isotopes,
63
Cu (isotopic mass = 62.9396 u) and
65
Cu
(64.9278 u). If copper has an average atomic mass of 63.546 u, what is the percent abundance of
each isotope?
f
1
+
f
2
= 1.000
f
2
= 1.000 –
f
1
average atomic mass =
f
1
M
1
+
f
2
M
2
average atomic mass =
f
1
M
1
+ (1.000 –
f
1
)
M
2
63.546 =
f
1
(64.9278) + (1.000 –
f
1
)(64.9278)
Solving for
f
1
:
f
1
= 0.695
(or 69.5%)
\
f
2
= 1.000 - 0.695
=
0.305
(or 30.5%)
%abundance of
63
Cu = ____
69.5%
________
%abundance of
65
Cu = ______
30.5%
________
Element
Mass Number
Number of
protons
Number of
electrons
Number of
neutrons
Charge
Sr
89
38
36
51
+2
Note: 1 mole CaCl
2
à
3 moles of ions (1 Ca
2+
+ 2 Cl
–
)
Note: 0.21% m/v = 0.21 g NaF/100 mL toothpaste
Note: n = MF mass/EF mass
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CHM1311 E FALL 2022
Page 2 of 2
6.
In an environmental test for dissolved iodide ion in saltwater, the iodide undergoes redox
chemistry in acidic solution, according to the following half-reactions:
I
–
(aq)
à
I
2
(s)
NO
3
–
(aq)
à
N
2
(g)
a)
(4 pts) Derive a balanced redox reaction,
including phases
.
Underline the reducing agent.
{
2 I
–
(aq)
à
I
2
(s)
+
2 e
–
}
X 5
10 I
–
(aq)
à
5 I
2
(s)
+
10 e
–
10 e
–
+
12 H
+
+
2 NO
3
–
(aq)
à
N
2
(g)
+
6 H
2
O
10 I
–
(aq)
+
12 H
+
(
aq
)
+
2 NO
3
–
(aq)
à
N
2
(g)
+
6 H
2
O (
l
)
+
5 I
2
(s)
Note: final answer must include phases to receive full points
b)
(3 pts) A 50.0 mL sample of seawater was found to react with 1.867 mL of a 0.0520 M
Ca(NO
3
)
2
solution. What was the molarity of iodide ion in the seawater sample?
TOTAL SCORE = ________ / 15
? mol I
–
=
0.001867 L
×
0.0520 mol Ca(NO
3
)
2
L
×
2 mol NO
3
–
1 mol Ca(NO
3
)
2
×
10 mol I
–
2 mol NO
3
–
=
0.000971 mol I
–
?
mol I
–
L
=
0.000971 mol
0.0500 L
=
0.0194 M
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CHM1311 Midterm 1 2022
Page 3 of 8
1. Short Answer Questions
a)
(1 pt) Four different compounds have the specific heat capacities shown below. If 100 g
of each compound, all starting at 20.0ºC, absorb 450 J of heat, which compound will have
the highest final temperature?
A
B
C
D
15 J/gºC
0.15 J/gºC
43 J/gºC
27 J/gºC
b)
(1 pt) A solution of NH
3
and H
2
O is 45% H
2
O
by mass
; NH
3
is the solvent.
True
False
c)
(1 pt) If the molar mass of a gas is
doubled
, the root-mean-squared speed of
the molecules will increase by a factor of:
d)
(1 pt) You take a 4.0 L volume of gas at 200 K. You expand the gas to an 8.0
L volume and simultaneously heat the vessel to 800 K. The pressure of the gas:
DOUBLES
HALVES
QUADRUPLES
STAYS CONSTANT
e)
(2 pts) Among the following, circle the compound with the highest oxidation state of
nitrogen and underline the compound with the lowest oxidation state of nitrogen.
NO
+
N
2
NO
3
–
NO
2
N
2
O
NH
3
f)
(2 pts) Starting with an atom of germanium-72, we add 3 protons, add 6 neutrons, and
add 4 electrons to the atom. Fill in the blanks for our new species:
Number of protons
Number of neutrons
Number of electrons
Chemical Symbol
35
46
36
!"
–
"#
$%
g)
(1 pt) The percent yield for two successive reactions, A
à
B and B
à
C,
are 45% and 79%, respectively. The overall percent yield for the
conversion of A to C is:
h)
(1 pt) The energy change shown in the diagram at right corresponds to an:
c
EXOTHERMIC CONTRACTION
c
ENDOTHERMIC CONTRACTION
c
EXOTHERMIC EXPANSION
n
ENDOTHERMIC EXPANSION
BONUS - For the hypothetical reaction below, carried out under constant pressure
conditions, which of the following are correct? Circle all that apply.
∆
V > 0
W > 0
∆
U = q + W
∆
V < 0
W < 0
∆
U > 0
∆
V = 0
W = 0
∆
U < 0
Energy
U
1
U
2
q
W
A (
g
) + 2 B (
l
)
à
3 C (
g
) + heat
!
1
2
%&
1
√2
36%
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CHM1311 Midterm 1 2022
Page 4 of 8
2. Barium sulfate is used as a radiocontrast agent for X-ray imaging of the digestive system.
A patient is given a beaker filled with a solution that contains 0.250% BaSO
4
by mass. The
density of the imaging solution is 1.45 g/mL.
THIS QUESTION IS SIMILAR TO EXAMPLES FROM MODULE 1
a)
(3 pts) What is the molarity of the solution?
?
)*+ ,-./
!
0
=
2. 452 6 ,-./
!
722 6 8*+9
×
7. ;5 6 8*+9
)0 8*+9
×
7222 )0
7 0
×
)*+ ,-./
!
4<<. <= 6 ,-./
!
= 0.0155 mol/L
b)
(3 pts) What is the molality of the solution?
100 g of solution contains 0.250 g of solute. What is the mass of the solvent?
m
soln
= m
solute
+ m
solvent
100 g = 0.250 g + m
solvent
m
solvent
= 99.750 g
?
)*+ ,-./
!
>6 ?
"
/
=
2. 452 6 ,-./
!
==. @52 6 ?
"
/
×
7222 6 ?
"
/
>6 ?
"
/
×
)*+ ,-./
!
4<<. <= 6 ,-./
!
= 0.0107 mol/kg
c)
(4 pts) The cylindrical beaker has a diameter of 8.00 cm and a height of 15.0 cm. Given
that the percent natural abundance of
134
Ba is 2.417%, how many
134
Ba atoms will be
ingested by the patient?
Recall:
volume of a cylinder =
p
r
2
h
A = BC
"
D = (B)(;. 22 G))
"
(75. 2 G)) = @5; G)
#
= 2. @5; 0
? "#$%&
("
!"#
= *. ,-. / ×
*. *1-- %$2 ("34
#
/ &$25
×
1 %$2 ("
1 %$2 ("34
#
×
6. *7781*
$"
"#$%& ("
%$2 ("
×
7. .1, "#$%&
("
!"#
1** "#$%& ("
= 1.70 x 10
20
atoms
134
Ba
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CHM1311 Midterm 1 2022
Page 5 of 8
3. A 3.902 g sample of an unknown compound containing only C, H, and O is combusted in
an oxygen-rich environment.
THIS QUESTION IS FROM 2014 MIDTERM 1 AND IS SIMILAR TO A MODULE 1 PROBLEM
a)
(3 pts) The CO
2
gas produced in the reaction is collected over water at 20.00ºC in a 5.000
L flask. The pressure in the flask is measured to be 100.52 kPa. What is the number of
moles of carbon dioxide gas produced in the combustion? The vapour pressure of water
at 20.00ºC is 2.3393 kPa.
b)
(5 pts) The reaction was found to also produce 3.633 g of liquid H
2
O. What is the empirical
formula of the unknown compound?
c)
(2 pts) If the molecular mass of the unknown compound is found to be 116.2 u, what is
its molecular formula?
P
total
=
P
CO
2
+
P
H
2
O
P
CO
2
=
P
total
−
P
H
2
O
=
100.52kPa-2.3393kPa
=
98.18kPa
? mol CO
2
=
P
CO
2
•V
RT
=
(98.18 kPa)(5.000 L)
(8.3145 kPa
⋅
L/mol
⋅
K)(293.15 K)
=
0.2014 mol
? mol C
=
0.2014 mol CO
2
×
1 mol C
1 mol CO
2
=
0.2014 mol C
? mol H
=
3.633 g H
2
O
×
mol H
2
O
18.02 g H
2
O
×
2 mol H
1 mol H
2
O
=
0.4032 mol H
? g C
=
0.2014 mol C
×
12.011 g C
1 mol C
=
2.42 g C
? g H
=
0.4031 mol H
×
1.008 g H
1 mol H
=
0.406 g H
∴
? g O
=
3.902 g sample – 2.42 g C – 0.406 g H
=
1.07 g O
? mol O
=
1.07 g O
×
1 mol O
15.999 g O
=
0.0669 mol O
∴
C
0.2014
0.0669
H
0.4032
0.0669
O
0.0669
0.0669
=
C
3
H
6
O
MF mass
EF mass
=
116 u
58 u
=
2
∴
MF
=
2
×
EF
=
C
6
H
12
O
2
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CHM1311 Midterm 1 2022
Page 6 of 8
4. In a constant-pressure calorimeter, 65.0 mL of 0.0800 M aqueous sulfuric acid was added
to 65.0 mL of 0.250 M aqueous sodium hydroxide. The reaction caused the temperature of
the solution to rise from 23.60°C to 25.10°C.
THIS QUESTION IS SIMILAR TO A Q FROM 2018 MIDTERM 1 AND A MODULE 3 PROBLEM
a)
(1 pt) This acid-base neutralization forms aqueous sodium sulfate and liquid water.
Write a balanced molecular equation (including phases) for the reaction.
H
2
SO
4
(
aq
)
+
2 NaOH (
aq
)
à
Na
2
SO
4
(
aq
)
+
2 H
2
O (
l
)
b)
(4 pts) If the solution has the same density and specific heat capacity as water, what is
Δ
H for this reaction, in kJ per mole of H
2
O produced? You may assume that the final total
volume of the solution is equal to the sum of the individual volumes.
? )*+ ?
"
/ HC*) ?
"
./
!
= 2. 2I52 0 ×
2. 2J22 )*+ ?
"
./
!
0
×
4 )*+ ?
"
/
7 )*+ ?
"
./
!
= 2. 272;2 )*+
? )*+ ?
"
/ HC*) K-/? = 2. 2I52 0 ×
2. 452 )*+ K-/?
0
×
4 )*+ ?
"
/
4 )*+ K-/?
= 2. 27I45 )*+
Therefore, the H
2
SO
4
is the limiting reagent.
q
reaction
= –q
surr
= – m
total
c
∆
T
= – (130 g)(4.184 J/gºC)(25.10ºC – 23.60ºC)
= –816 J
∆M =
N
O
=
– 816 S
0.01040 VWX
×
1 YS
1000 S
= 78.4 YS
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CHM1311 Midterm 1 2022
Page 7 of 8
5. Methane (CH
4
) and chlorine gas react at high temperature to form chloromethane (CH
3
Cl)
and hydrogen chloride.
a)
(4 pts) If this reaction has a 75.0% yield, what mass (in g) of chloromethane will form
when 20.5 g of methane and 45.0 g of chlorine gas are reacted together?
THIS QUESTION IS SUGGESTED SILBERBERG PROBLEM 3.88
CH
4
(
g
)
+
Cl
2
(
g
)
à
CH
3
Cl (
g
)
+
HCl (
g
)
? )*+ [?
#
[+ HC*) [?
!
= 42. 5 6 [?
!
×
)*+ [?
!
7I. 2; 6 [?
!
×
7 )*+ [?
#
[+
7 )*+ [?
!
= 7. 4J )*+
? )*+ [?
#
[+ HC*) [+
"
= ;5. 2 6 [+
"
×
)*+ [+
"
@2. = 6 [+
"
×
7 )*+ [?
#
[+
7 )*+ [+
"
= 2. I<5 )*+
Therefore, the Cl
2
is the limiting reagent.
? 6 [?
#
[+ = 2. I<5 )*+ ×
52. ;J 6
)*+
× 2. @52 = 4;. 2 6
b)
(2 pts) When carried out under constant pressure conditions entirely in the gas phase at
450 K, the above reaction absorbs 788 J of heat. Determine
∆
U for the reaction, in kJ/mol.
FOR THIS QUESTION, THE FOLLOWING TWO SOLUTIONS ARE ACCEPTED:
W = –P
∆
V = –
∆
n
gas
RT
= –(0 mol)(8.3145 J/mol•K)(450 K)
= 0 J
(no work is done!)
∆
U = q
P
+ W
=
∆
H
=
+@JJ ]
2. I<5 )*+
= 1240 J/mol
= 1.24 kJ/mol
c)
(1 pt) On the following template, draw a representative
energy diagram for the reaction, labelling U
1
, U
2
,
∆
U, q and
W.
Energy
U
1
U
2
∆
U
q
W = zero!
W = –P
∆
V = –
∆
n
gas
RT
= –(0 mol)(8.3145 J/mol•K)(450 K)
= 0 J
(no work is done!)
∆
U = q
P
+ W
=
∆
H
=
+@JJ ]
(2. I<5 )*+)(2. @5)
= 1655 J/mol
= 1.66 kJ/mol
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CHM1311 Midterm 1 2022
Page 8 of 8
6. Dr. Fox decides to demonstrate Boyle’s law while scuba diving. She takes a syringe filled
with 18.0 mL of air from the surface (which is at an atmospheric pressure of 1.014 bar and a
temperature of 25.95ºC) with her on a dive to a depth of 12 m.
THIS QUESTION IS A REVISED VERSION OF A PROBLEM FROM MIDTERM 1 2015
a)
(3 pts) During the dive, the volume of the air in the syringe drops to 5.40 mL and the
temperature drops to 23.12ºC. What is the pressure in the syringe at this depth, in bars?
^
$
A
$
_
$
=
^
"
A
"
_
"
^
"
=
^
$
A
$
_
$
×
_
"
A
"
=
(7. 27; `-C)(7J. 2 )0)(4=I. 42 a)
(4==. 72 a)(5. ;2 )0)
= <. <5 `-C
b)
(1 pt) Under which condition do the gas molecules in
the syringe have the greater average kinetic energy?
c)
(1 pt) The air sample contains nitrogen and oxygen
gases. Which gas has the greatest root-mean-squared
speed?
d)
(3 pts) If the mole fraction of oxygen in air is 0.209, calculate the number of moles of
oxygen in the syringe.
P
O
2
=
χ
O
2
×
P
T
=
0.209
×
1.014 bar
=
0.212 bar
T
=
25.95
+
273.15
=
299.1 K
?molO
2
=
PV
RT
=
0.212 bar
×
0.0180 L
0.083145L
⋅
bar
⋅
mol
–1
⋅
K
–1
×
299.91 K
=
0.000153 mol
n
AT THE SURFACE (at 0 m)
c
UNDERWATER (at 12 m)
n
N
2
at 0 m
c
N
2
at 12 m
c
O
2
at 0 m
c
O
2
at 12 m
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CHM1311 – Midterm 2 – 2022
Page 3 of 9
1.
(10 pts) Short Answer Questions
a)
(2 pts) In the reaction: N
2
O
4
(g)
D
2 NO
2
(g) (
∆
H = 57.2 kJ/mol), the reactant is a colourless
gas and the product is a brown gas. A flask contains a mixture of these gases at
equilibrium. In the box, write the equilibrium constant and choose the best means which
would lead to an increase in the observed colour.
£
remove NO
2
and remove heat
£
add NO
2
and decrease volume
£
remove N
2
O
4
and add heat
£
add N
2
O
4
and increase volume
b)
(1 pt) The standard heat of formation of solid ammonium chloride is –314 kJ. Write the
chemical equation for the reaction to which this value applies.
½
N
2
(g)
+
2 H
2
(g)
+
½
Cl
2
(g)
à
NH
4
Cl (s)
c)
(1 pt) The conjugate acid and conjugate base of HPO
4
2–
are _______
H
2
PO
4
–
___________
and __________
PO
4
3–
_________
respectively.
d)
(1 pt) Which of the following would be the correct van’t Hoff plot for an endothermic
reaction?
e)
(0.5 pt) Which of the following ions is the weakest base?
N
3
-
NO
2
-
F
-
HO
2
-
f)
(1 pt) Circle the two ‘ingredients’ you would use to prepare a buffer of pH = 9.05.
CH
3
COOH
HOCl
NaOH
HCN
CH
3
COONa
NaCl
HCl
KCN
lnK
1/T
A
B
C
D
lnK
1/T
lnK
1/T
lnK
1/T
K =
(P
NO
2
)
2
P
N
2
O
4
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CHM1311 – Midterm 2 – 2022
Page 4 of 9
g)
(2 pts) In the following list, circle the acidic salt(s) and underline the basic salt(s).
LiCl
NaF
NH
4
Br
TiCl
4
KNO
3
NaN
3
h)
(0.5 pt) Bond breaking is always an endothermic process.
TRUE
FALSE
i)
(0.5 pt) A chemical equilibrium can be considered to be “going to completion” when
the value of K is at least
10
–10
10
–5
10
10
5
or
greater.
j)
(0.5 pt) A buffer made from HA (pK
a
= 4.82) and NaA has a pH of 4.75. The buffer
therefore contains:
[HA] > [A
–
]
[HA] < [A
–
]
[HA] = [A
–
]
BONUS
Give the expected products of the following acid-base reaction, label the acid, base,
conjugate acid, and conjugate base, and determine the preferred direction of the
equilibrium.
Cl
–
+
HNO
2
D
HCl
+
NO
2
–
K > 1
K < 1
base
acid
conj. acid
conj. base
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CHM1311 – Midterm 2 – 2022
Page 5 of 9
2.
The following reaction takes place entirely in the gas phase at 550 K:
THIS IS A NEW QUESTION
a)
(3 pts) Using the table of bond energies, estimate the energy change of the reaction. Show
your work to receive all points.
BROKEN:
1 x C–C
1 x 348 kJ
348 kJ
1 x H–H
2 x 436 kJ
436 kJ
TOTAL
+ 784 kJ
FORMED:
2 x C–H
2 x 413 kJ
–826 kJ
TOTAL
–826 kJ
∆
E = +784 kJ + (–826 kJ) = –42.0 kJ
b)
(3 pts) Using the table of
∆
H
f
º values, determine the enthalpy change of the reaction.
Show your work to receive all points.
∆
Hº = {
∑
(
∆
H
f
º(pdts)} – {
∑
(
∆
H
f
º(rxts)}
= [(C
6
H
6
(
g
)) + (CH
4
(
g
))] – [(C
6
H
5
CH
3
(
g
)) + (H
2
(
g
))]
= [(82.9) + (–74.8)] – [(50.1) + (0)] kJ/mol
= –42.0 kJ/mol
c)
(1 pt) Which of the following energy diagrams best represents the reaction?
A
B
C
D
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
C
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
+
+
ENERGY
U
1
U
2
q
ENERGY
U
1
U
2
q
ENERGY
U
2
U
1
q
ENERGY
U
2
U
1
q
Bond
Energy (kJ/mol)
C–C
348
C=C
612
H–H
436
C–H
413
Compound
∆
H
f
º (kJ/mol)
C
6
H
5
CH
3
(
l
)
12.0
C
6
H
5
CH
3
(
g
)
50.1
C
6
H
6
(
l
)
49.0
C
6
H
6
(
g
)
82.9
CH
4
(
g
)
–74.8
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CHM1311 – Midterm 2 – 2022
Page 6 of 9
3.
An engineer who is examining the oxidation of SO
2
in the manufacture of sulfuric acid
determines that K
c
= 1.7x10
8
at 600. K :
2 SO
2
(
g
) + O
2
(
g
)
D
2 SO
3
(
g
)
THIS IS SILBERBERG SUGGESTED PROBLEM 15.87
a)
(2 pts) What is the value of K
P
?
K
P
= K
C
(RT)
∆
n
= (1.7x10
8
)(0.083145 x 600)
2 – 3
= 3.4x10
6
b)
(2 pts) At equilibrium, P
SO3
= 300. bar and P
O2
= 100. bar. Calculate P
SO2
, in bars.
!
!
=
($
"#
!
)
$
&$
"#
"
'
$
($
#
"
)
$
"#
"
= (
($
"#
!
)
$
($
#
"
)(!
!
)
= (
()**)
$
(). ,-.*
%
)(.**)
= *. *./ 123
c)
(1 pt) In another experiment, the engineer places a mixture of 0.0040 mol of SO
2
, 0.0028
mol of O
2
and 0.0034 mol of SO
3
in a 1.00 L flask at 600. K. In which direction will the
reaction proceed?
TOWARDS REACTANTS
TOWARDS PRODUCTS
ALREADY AT EQUILIBRIUM
d)
(3 pts) In the second step of the process, the sulfur trioxide is converted to sulfuric acid:
SO
3
(
g
) + H
2
O(
g
)
D
H
2
SO
4
(
g
)
K
c
= 3.4x10
3
at 600. K
Given this information, determine K
c
for the overall conversion of SO
3
to H
2
SO
4
:
2 SO
2
(
g
) + O
2
(
g
) + 2 H
2
O(
g
)
D
2 H
2
SO
4
(
g
)
K
c
= ? at 600. K
1
2 SO
2
(
g
) + O
2
(
g
)
D
2 SO
3
(
g
)
K
1
= 1.7x10
8
2
SO
3
(
g
) + H
2
O(
g
)
D
H
2
SO
4
(
g
)
K
2
= 3.4x10
3
3
=
2
x 2
2 SO
3
(
g
) + 2 H
2
O(
g
)
D
2 H
2
SO
4
(
g
)
K
3
= (K
2
)
2
= 1.2x10
7
4
=
1
+
3
2 SO
2
(
g
) + O
2
(
g
) + 2 H
2
O(
g
)
D
2 H
2
SO
4
(
g
)
K
4
= K
1
x K
3
= 2.0x10
15
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CHM1311 – Midterm 2 – 2022
Page 7 of 9
4.
Two FBI agents, Mulder and Scully, are investigating a series of strange murders. In each
case, the victim was found suspended in a solution of ammonium benzoate, NH
4
C
7
H
5
O
2
.
THIS IS FROM MIDTERM 2 2015
a)
(4 pts) Will these salt solutions be acidic, basic, or neutral? Show your reasoning to earn
full points. (K
b
of ammonia is 1.8 x 10
–5
).
Dissolution of the salt:
NH
4
C
7
H
5
O
2
(s)
à
NH
4
+
(aq)
+
C
7
H
5
O
2
–
(aq)
Both ions will hydrolyze, so which one hydrolyzes more? (Let’s keep 1 extra sig fig)
NH
4
+
+
H
2
O
D
NH
3
+
H
3
O
+
C
7
H
5
O
2
–
+
H
2
O
D
HC
7
H
5
O
2
+
OH
–
Since K
a
> K
b
, we know that the first equilibrium favours the products more. Therefore, the
solution should be ACIDIC.
b)
(6 pts) Agent Scully determines that the solution concentration is 0.128 M. What is the
exact pH of the solution?
NH
4
+
+
H
2
O
D
H
3
O
+
+
NH
3
I
0.128
-
0
0
C
-
x
-
+
x
+
x
E
0.128 -
x
-
x
x
C
7
H
5
O
2
–
+
H
2
O
D
HC
7
H
5
O
2
+
OH
–
I
0.128
-
0
0
C
-
x
-
+
x
+
x
E
0.128 -
x
-
x
x
[H
3
O
+
] > [OH
–
], therefore, the excess H
3
O
+
will determine the pH of the solution:
leftover [H
3
O
+
] = 8.44x10
–6
– 4.51x10
–6
= 3.93x10
–6
M
pH = –log(3.93x10
–6
) = 5.41
K
a
=
K
W
K
b
=
1.0
x
10
–14
1.8
x
10
–5
=
5.56
x
10
–10
K
b
=
K
W
K
a
=
1.0
x
10
–14
6.3
x
10
–5
=
1.59
x
10
–10
K
b
=
K
W
K
a
=
[OH
–
][HC
7
H
5
O
2
]
[C
7
H
5
O
2
–
]
1.59x10
–10
=
x
2
0.128 –
x
≈
x
2
0.128
∴
x
≈
4.51x10
–6
M
=
[OH
–
]
Check:
4.51x10
–6
0.128
×
100%
=
0.003%
$ →
$
PASSES
K
a
=
[H
3
O
+
][NH
3
]
[NH
4
+
]
5.56
x
1
0
–10
=
x
2
0.128 –
x
≈
x
2
∴
x
≈
8.44x10
–6
M
=
[H
3
O
+
]
Check:
8.44x10
–6
0.128
×
100%
=
0.006%
$ →
$
PASSES
0.128
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CHM1311 – Midterm 2 – 2022
Page 8 of 9
5.
A buffer that contains 0.220 M HA and 0.297 M A
–
has a pH of 3.87.
THIS IS FROM MIDTERM 2 2015
a)
(4 pts) What is the pK
a
of the buffer?
b)
(6 pts) What is the change in pH after 0.0015 mol of Ba(OH)
2
is added to 0.500 L of this
buffer solution? Ba(OH)
2
dissolves completely; the Ba
2+
(
aq
) ion has no acid-base
character.
BONUS – What are HA and A
–
? (Give their formulas). Show your reasoning.
Since pK
a
= 3.74, K
a
= 10
–3.74
= 1.8x10
–4
From the K
a
table in the data sheets, we see that this corresponds to HCHO
2
.
Therefore, HA and A
–
are HCHO
2
and CHO
2
–
, respectively.
pH
=
pK
a
+
log
[A
–
]
[HA]
!
"
#
$
%
&
3.87
=
pK
a
+ log
0.297
0.220
!
"
#
$
%
&
pK
a
=
3.74
?
mol OH
–
L
added
=
0.0015 mol Ba(OH)
2
0.500 L
×
2 mol OH
–
1 mol Ba(OH)
2
=
0.0060 M
pH
=
pK
a
+
log
[A
–
]
[HA]
!
"
#
$
%
&
=
3.74
+
log
0.303
0.214
!
"
#
$
%
&
=
3.89
∴
∆
pH
=
pH
2
−
pH
1
=
3.89
−
3.87
=
+0.02
HA +
OH
–
D
A
–
+ H
2
O
B
0.220
0.297
-
A
0.006
-
M
-0.006
-0.006
+0.006
-
A
0.214
0
0.303
-
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CHM1311 – Midterm 2 – 2022
Page 9 of 9
6.
(5 pts) After a vacation of scuba-diving, Dr. Fox has to clean and rinse all her scuba gear
before putting it back into storage. She wants to use “
Diver’s Buddy Scuba Shampoo
”, a
commercially available aqueous solution of trimethylamine (N(CH
3
)
3
, K
b
= 6.31 x 10
–6
).
Dr. Fox measures the pH of the solution and finds it to be 10.05. What is the concentration
of trimethylamine in the shampoo, in mol/L?
THIS IS FROM MIDTERM 2 2018
pOH = 14 – pH = 3.95
[OH
–
] = 10
–3.95
= 1.12 x 10
–4
M
Let B represent the base, N(CH
3
)
3
.
B
+
H
2
O
D
OH
–
+
HB
+
I
[B]
o
-
0
0
C
-
x
-
+
x
+
x
E
[B]
o
-
x
-
x
x
x = [OH
–
] = 1.12 x 10
–4
M
/. ).-.*
&%
=
(.. .4-.*
&'
)
$
[6]
(
− .. .4-.*
&'
/. ).-.*
&%
[6]
(
− 9. *9-.*
&)*
= .. 4:-.*
&+
[B]
o
= 0.0021 M
[B]
eqm
= [B]
o
–
x
= 0.0020 M
Note:
I will accept either [B]
o
or [B]
eqm
as your final answer.
K
b
=
[OH
–
][HB
+
]
[B]
6.31x10
–6
=
x
2
[
B]
o
–
x
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CHM1311 E – Final Exam 2022
Page 3 of 14
1.
Short Answer Questions.
a)
(0.5 pt) Which of the following isotopes has the greatest number of neutrons?
b)
(1 pt) An aqueous solution of sulphuric acid has a concentration of 2.45 mol/kg.
The
mole fraction of H
2
SO
4
in this mixture is : ____
0.042
___________________
c)
(2 pts) The contents of two test tubes, containing AgNO
3
(
aq
) and CaCl
2
(
aq
), are mixed
together. Write the balanced molecular equation for the expected precipitation (if any)
including phases:
d)
(0.5 pt) 1.0 mol of an ideal gas is placed in a 1.0 L flask at 22ºC. Which of the following
would result in the greatest increase in the pressure of the gas?
£
reducing the volume of the container to 0.50 L
£
increasing the amount of gas to 1.5 mol
£
increasing the temperature to 300ºC
e)
(0.5 pt) Below is a hypothetical configuration for the ground state of a scandium atom.
This configuration is incorrect because:
1s
2
2s
2
2p
6
3s
2
3p
6
3d
1
4s
2
£
it contains one or more orbitals that do not exist
£
it contains too few electrons
£
it contains too many electrons
£
it contains electrons in incorrect orbitals
£
it contains orbitals listed in incorrect order
f)
(0.5 pt) A student draws the orbital energy diagram at right for a carbon atom. As shown,
this diagram:
£
is correct
£
disobeys the Pauli Exclusion Principle
£
disobeys Hund’s Rule
£
disobeys the Aufbau Principle
17
35
Cl
19
40
K
17
37
Cl
20
40
Ca
E
1s
2s
2p
2 AgNO
3
(
aq
) + CaCl
2
(
aq
)
à
2 AgCl (
s
)
+
Ca(NO
3
)
2
(
aq
)
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CHM1311 E – Final Exam 2022
Page 4 of 14
g)
(1 pt) The number of atoms in 10.0 g of CaCO
3
(100.0 g/mol) is:
1.81 x 10
23
6.02 x 10
22
3.01 x 10
23
1.21 x 10
23
h)
(0.5 pt) For the orbital shown on the 3D axes provided at right, a possible
set of quantum numbers would be n = 3,
l
= __
2
____ , m
l
= – 2.
i)
(1 pt) Given the information below, the value of the equilibrium constant for the reaction
A(g)
+
B(g)
D
2C(g)
is = _____
0.83
_______________.
2A(g)
D
2X(g)
K
P
= 35.5
2C(g)
D
X(g)
+
B(g)
K
P
= 7.2
j)
(1 pt) The standard heat of formation of solid ammonium chloride is –314 kJ. Write the
chemical equation for the reaction to which this value applies (including phases).
k)
(1 pt) For the compounds listed below, how many will be
more
soluble in a pH = 4.5
buffer than in pure water?
NONE
1
2
3
ALL OF THEM
PbI
2
CaCO
3
BaF
2
Zn(OH)
2
l)
(2 pts) For a first order reaction, the half-life
__
does not change
____
with increasing
reactant concentration. For a second order reaction, the half-life ____
decreases
____ with
increasing reactant concentration.
m)
(1 pt) A one litre balloon is filled with neon gas. A hole is made in the balloon and the
gas effuses at a rate of 0.0280 mol/hr. If the same balloon is refilled with argon at the
same pressure and temperature, its rate of effusion would be ____
0.020
________.
n)
(0.5 pt) It is possible to prepare a buffer by taking a strong base and titrating it with a
strong acid to the half equivalence point.
TRUE
FALSE
x
y
z
½ N
2
(
g
)
+ 2 H
2
(
g
)
+ ½ Cl
2
(
g
)
à
NH
4
Cl (
s
)
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CHM1311 E – Final Exam 2022
Page 5 of 14
o)
(1 pt) The figure on the left shows 1
mol
of
gas
in
an
open-end
manometer. The external pressure is
1.0 bar and the temperature is 300K.
In the box, sketch the manometer
and qualitatively show the effect on
the gas if the external pressure
increases
to
2.0
bar
and
the
temperature of the gas is increased
to 600K.
p)
(1 pt) Solid potassium chromate is slowly added to an aqueous solution that contains
0.200 M each Pb
2+
and Ag
+
ions. The compound that precipitates first is:
__
PbCrO
4
__________.
q)
(1 pt) For an ideal gas, a graph of PV versus T will be a linear relationship with a slope
that is directly proportional to the gas’s:
KINETIC ENERGY
MOLAR MASS
ENTHALPY
MASS
r)
(2 pts) For the hypothetical reaction below, carried out under constant pressure
conditions, which of the following are correct? Circle all that apply.
∆
V > 0
W > 0
∆
U = q + W
∆
V < 0
W < 0
∆
U > 0
∆
V = 0
W = 0
∆
U < 0
s)
(1 pt) Name two ways to accelerate a chemical reaction.
•
increase the concentration of the reactants
•
increase temperature
•
increase surface area of reactants/contact surfaces between reactants
•
add a catalyst
A (
g
) + 2 B (
l
)
à
3 C (
g
) + heat
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CHM1311 E – Final Exam 2022
Page 6 of 14
t)
(1 pt) The graph at right represents the concentrations as a function of time for the
reaction A(g)
D
B(g). Which of the following statements is/are true? Select all that apply.
c
K
P
is equal to 1
c
K
P
is greater than 1
c
K
P
is less than 1
c
K
P
is equal to K
C
c
The system never reaches equilibrium
BONUS 1
Sulfurous acid (H
2
SO
3
) has pK
a1
= 1.85 and pKa
2
= 7.20. An aqueous solution of this acid is
titrated with NaOH (aq). At the
second
equivalence point, the pH of the solution will be
ACIDIC
BASIC
NEUTRAL
Write the chemical equation for the expected hydrolysis (no phases necessary):
BONUS 2
Most of the students registered in this course aren’t studying chemistry, but this course is
mandatory for so many programs because it covers a lot of fundamental science required for
other disciplines and it also trains you in problem-solving. Describe an occasion where you
were able to apply a concept from CHM1311 elsewhere (in another course, in your daily life,
etc
.). If you can’t think of an example, then describe a favourite fact or concept you learned
this term in CHM1311.
Concentration
Time
A
B
SO
3
2–
+
H
2
O
D
HSO
3
–
+
OH
–
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CHM1311 E – Final Exam 2022
Page 7 of 14
2.
You wish to prepare a buffer solution with pH = 9.45.
a)
(5 pts) How many grams of (NH
4
)
2
SO
4
would you add to 425 mL of 0.258 M NH
3
to do
this? You may assume that the solution’s volume remains constant. K
b
of NH
3
= 1.8x10
-5
Answer: _______
4.7 g
____________
b)
(5 pts) You have access to additional 0.258 M NH
3
and more solid (NH
4
)
2
SO
4
. Which
buffer component, and how much (in g or mL) would you add to 0.100 L of the buffer in
part (a) to change its pH to 9.30? You may assume that the solution’s volume remains
constant.
Component: __
(NH
4
)
2
SO
4
__________
Amount: ___
0.46 g
_________
[NH
4
+
] = [NH
3
] / 1.55 = 0.17 M
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CHM1311 E – Final Exam 2022
Page 8 of 14
3.
Peroxyacetyl nitrate (PAN) is an air pollutant
produced during photochemical smog events.
PAN is unstable and dissociates as shown at right.
a)
(3 pts) Using the data in the table below, derive a rate law for the decomposition of PAN
at 25.0ºC, as well as the value of the rate constant (with appropriate units).
Trial
Initial [PAN]
(M)
Initial Rate
(M/min)
1
8.30x10
–10
1.92x10
–11
2
1.66x10
–9
3.84x10
–11
3
2.49x10
–9
5.78x10
–11
Rate law is:
___
rate = k[PAN]
___________
Rate constant is:
___
k = 0.0231 min
–1
_________
b)
(2 pts) The decomposition of PAN has a half-life of 35.0 hr at 0.00ºC. What is the rate
constant for this reaction at this temperature? Use the same units as part (a).
It’s first order, so:
c)
(3 pts) What is the activation energy, in kJ/mol, for this reaction?
k
1
= 2.31x10
–2
min
–1
@ T
1
= 298 K
k
2
= 3.30x10
–4
min
–1
@ T
2
= 273 K
Solve for E
a
:
E
a
= 1.15x10
5
J/mol = 115 kJ/mol
d)
(2
pts)
The
enthalpy
for
the
decomposition of PAN is about 88
kJ/mol. On the axes provided, draw a
representative reaction profile for this
reaction,
with labels
.
k
=
rate
[PAN]
=
1.92
×
10
–11
M
⋅
min
–1
8.30
×
10
–10
M
=
2.31
×
10
–2
min
–1
t
1
2
=
ln2
k
∴
k
=
ln2
t
1
2
=
ln2
35.0 hr
•
1 hr
60 min
=
3.30
×
10
–4
min
–1
ln
k
2
k
1
!
"
#
$
%
&
=
−
E
a
R
1
T
2
−
1
T
1
!
"
#
$
%
&
⇒
ln
3.30
×
10
–
4
min
–
1
2.31
×
10
–
2
min
–
1
!
"
#
$
%
&
=
−
E
a
8.3145J
⋅
mol
–1
K
–1
1
273K
−
1
298K
!
"
#
$
%
&
CH
3
COONO
2
CH
3
COO
+
NO
2
O
O
PAN
Trials 1 & 2:
[PAN] x 2
à
rate x 2
Or:
Trials 1 & 3:
[PAN] x 3
à
rate x 3
\
rate = k[PAN]
(it’s first order)
reaction coordinate
Energy
∆
H = 88 kJ/mol
PAN (rxt)
products
E
a
= 115 kJ/mol
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CHM1311 E – Final Exam 2022
Page 9 of 14
4.
Electrons in Atoms.
a)
(3 pts) For the following sets of quantum numbers, give the subshell label, the allowed
values of
m
l
and the number of orbitals in the subshell (the first row is an example).
n
and
l
subshell label
m
l
values
number of orbitals
n
= 1 and
l
= 0
1
s
0
1
n
= 3
and
l
= 1
3p
-1, 0 , +1
3
n
= 5 and
l
= 2
5d
-2, -1, 0, +1, +2
5
b)
(3 pts) How many electrons can be described by each of the following sets of quantum
numbers?
i.
n
= 4,
l
= 2,
m
l
= 3
No such orbital exists (impossible value of m
l
)
ii.
n
= 3,
l
= 2,
m
l
= -1,
m
s
= –
½
1 electron
iii.
n
= 4,
l
= 3
4f orbitals = 7 orbitals x 2e
–
each = 14 electrons
c)
(4 pts) Draw a diagram of Bohr’s model of the hydrogen atom showing the transition of
an electron from the
n
= 5 level to the ground state. What is the change in energy (in
kJ/mol) of this transition?
Ground state means
n
= 1, therefore the transition is from
n
= 5 to
n
= 1:
∆" $%&
'(
)*+
, = – (0. 234526
–"#
() $
2
2
$
−
2
9
$
, $
2 '(
2666 (
, :
;. 600526
$%
<=*>*&?
)*+
@
= – 20;6 '(/)*+
Answer: _______________________________
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CHM1311 E – Final Exam 2022
Page 10 of 14
5.
A 125 g stainless steel ball (c = 0.50 J/gºC) at 525ºC is dropped into 75.0 mL of water at
28.5ºC in an open Styrofoam cup. You observe the release of some steam.
a)
(7 pts) Using values from the data sheets, calculate the mass (in g) of the steam that
escaped.
Let’s define:
q
1
= heat needed to raise temp of water to 100ºC
q
2
= heat needed to boil water at 100ºC
Thus q
H2O
= q
1
+ q
2
Mass of steam: _______
1.8 g
__________
b)
(3 pts) A second identically-sized ball, made from a metal with a higher specific heat
capacity than stainless steel, is subjected to the same conditions as part (a). Do you expect
the mass of produced steam to be greater or smaller? Explain.
If the specific heat capacity is higher, then the amount of heat released by the ball is
larger. Thus the heat absorbed by the water is greater. Since the amount of heat needed
to raise the temperature of the water is unchanged (q
1
is the same), that means more heat
is leftover to boil the water (q
2
is larger). Therefore more steam will be produced.
q
ball
=
m
ball
×
s
ball
×
∆
T
ball
=
(125
g
)(0.50
J
/
g
º
C
)(100º
C
−
525º
C
)
=
–2.656
x
10
4
J
∴
heat absorbed by water
=
q
H
2
O
= +
2.656
x
10
4
J
q
1
=
m
H
2
O
×
s
H
2
O
×
∆
T
H
2
O
=
(75.0
g
)(4.185
J
/
g
º
C
)(100º
C
−
28.5º
C
)
= +
2.244
x
10
4
J
q
2
=
q
H
2
O
−
q
1
=
2.656
x
10
4
J
−
2.244
x
10
4
J
=
4120
J
?
g steam
=
4120
J
×
mol H
2
O
40.7
x
10
3
J
×
18.02
g H
2
O
mol H
2
O
=
1.8
g
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CHM1311 E – Final Exam 2022
Page 11 of 14
6.
Dr. Fox decides to demonstrate Boyle’s law while scuba diving. She takes a syringe filled
with 18.0 mL of air from the surface (which is at an atmospheric pressure of 1.014 bar and
a temperature of 25.95ºC) with her on a dive to a depth of 12 m.
a)
(3 pts) During the dive, the volume of the air in the syringe drops to 5.40 mL and the
temperature drops to 23.12ºC. What is the pressure in the syringe at this depth, in bars?
B
"
C
"
D
"
=
B
$
C
$
D
$
B
$
=
B
"
C
"
D
"
×
D
$
C
$
=
(2. 62F GHI)(2J. 6 )K)(04;. 06 L)
(044. 26 L)(9. F6 )K)
= M. M9 GHI
b)
(1 pt) Under which condition do the gas molecules in
the syringe have the greater average kinetic energy?
c)
(3 pts) If the mole fraction of oxygen in air is 0.209, calculate the number of moles of
oxygen in the syringe.
d)
(3 pts) Match the three gases shown with
the
expected
molecular
speed
distribution diagrams (A, B, C) at right.
P
O
2
=
χ
O
2
×
P
T
=
0.209
×
1.014 bar
=
0.212 bar
T
=
25.95
+
273.15
=
299.1 K
?molO
2
=
PV
RT
=
0.212 bar
×
0.0180 L
0.083145L
⋅
bar
⋅
mol
–1
⋅
K
–1
×
299.91 K
=
0.000153 mol
c
AT THE SURFACE (at 0 m)
c
UNDERWATER (at 12 m)
NUMBER OF MOLECULES
ROOT-MEAN-SQUARED SPEED
A
B
C
______
N
2
at 0 m
______
O
2
at 12 m
______
N
2
at 12 m
A
B
C
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CHM1311 E – Final Exam 2022
Page 12 of 14
7.
You are performing a titration of
100.0 mL of 0.110 M HC
7
H
5
O
2
with 0.110 M NaOH. Determine
the pH of the solution:
a)
(3 pts) initially
b)
(2 pts) at the half-equivalence
point
c)
(4 pts) at the equivalence point
d)
(1 pt) Use these values to sketch
a titration curve on the graph
provided.
a) initial pH:
HA
+
H
2
O
D
H
3
O
+
+
A
–
I
0.110
-
0
0
C
–
x
-
+
x
+
x
E
0.110 –
x
-
x
x
pH = –log(0.0026) = 2.57
b) At the
½
equivalence point: pH = pK
a
= –log(6.3x10
–5
) = 4.20
(after 50 mL added)
c) At the equivalence point:
mol HA = mol OH
–
added = 0.0110 mol (this corresponds to adding 100.0 mL of base)
new [A
–
] = 0.0110 mol/(0.100 L + 0.100 L) = 0.0550 M
Benzoate (C
7
H
5
O
2
–
) is the conjugate base of a weak acid, so it hydrolyzes:
A
–
+ H
2
O
D
HA
+
OH
–
I
0.0550
-
0
0
C
-
x
-
+
x
+
x
E
0.055 -
x
-
x
x
pOH = –log(5.6x10
–6
) = 5.53
pH = 14 – 5.53 = 8.47
0
2
4
6
8
10
12
14
0
20
40
60
80
100
120
140
pH
mL OH
–
added
K
a
=
[H
3
O
+
][A
–
]
[HA]
6.3
×
1
0
–5
=
x
2
0.110 –
x
≈
x
2
0.110
∴
x
≈
0.0026 M
=
[H
3
O
+
]
Check:
0.0026
0.110
×
100%
=
2.4
%
⎯ →
⎯
PASSES
K
b
=
K
W
K
a
=
[HA][OH
–
]
[A
–
]
1.0
x
1
0
–14
6.3
x
1
0
–5
=
1.6
x
1
0
–10
=
x
2
0.055 –
x
≈
x
2
0.055
∴
x
≈
2.9x10
–6
M
=
[OH
–
]
Check:
2.9x10
–6
0.055
×
100%
=
0.005%
⎯ →
⎯
PASSES
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CHM1311 E – Final Exam 2022
Page 13 of 14
8.
Barium sulfate is used in medical imaging of the gastrointestinal tract because it is
opaque to X rays. A barium sulfate solution is ingested by the patient, whose stomach
and intestines can then be visualized via X-ray imaging.
a)
(5 pts) If a patient ingests 200 mL of a saturated barium sulfate solution, how many toxic
Ba
2+
ions has the patient consumed?
K
sp
of BaSO
4
= 1.1 x 10
-10
Let s represent the solubility of barium sulfate:
BaSO
4
(s)
D
Ba
2+
(aq)
+
SO
4
2–
(aq)
I
m
0
0
C
–s
+s
+s
E
m – s
s
s
K
sp
= [Ba
2+
][SO
4
2–
] = s
2
s =
√
K
sp
=
√
(1.1x10
–10
) = 1.05x10
–5
M = [Ba
2+
]
b)
(3 pts) There are some data that suggest that zinc lozenges can significantly shorten the
duration of a cold. If the solubility of zinc acetate, Zn(CH
3
COO)
2
, is 43.0 g/L, what is the
K
sp
of this compound?
Let s represent the solubility of zinc acetate:
Zn(CH
3
COO)
2
(s)
D
Zn
2+
(aq)
+
2 CH
3
COO
–
(aq)
I
m
0
0
C
–s
+s
+2s
E
m – s
s
2s
K
sp
= [Zn
2+
][CH
3
COO
–
]
2
= (s)(2s)
2
= 4s
3
= 4 x (0.234)
3
= 0.051
c)
(2 pts) How might one use pH to improve the solubility of zinc acetate? Explain, using
Le Chatelier’s Principle.
The anion formed in the dissolution, acetate, is the CONJUGATE BASE of a WEAK ACID.
Therefore, it will HYDROLYZE when added to water:
CH
3
COO
–
+
H
2
O
D
CH
3
COOH
+
OH
–
Thus, this salt will be MORE SOLUBLE in ACIDIC SOLUTIONS (because the acid will
consume the produced OH
–
and pull the equilibrium forward).
? Ba
2+
ions
=
200 mL
×
1 L
1000 mL
×
1.05
x
10
–5
mol Ba
2+
L
×
6.022
x
10
23
Ba
2+
ions
mol Ba
2+
ions
=
1.3
x
10
18
ions
s
=
? mol Zn(CH
3
COO)
2
L
=
43.0 g Zn(CH
3
COO)
2
1 L
×
mol Zn(CH
3
COO)
2
183.5 g Zn(CH
3
COO)
2
=
0.234 mol/L
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CHM1311 E – Final Exam 2022
Page 14 of 14
9.
Chlorine gas can be generated by the following redox process:
a)
(3 pts) Find the overall balanced redox reaction, under acidic conditions.
{
5 e
–
+
8 H
+
(
aq
) +
MnO
4
–
(
aq
)
à
Mn
2+
(
aq
)
+
4 H
2
O (
l
)
}
X 2
{
2 Cl
–
(
aq
)
à
Cl
2
(
g
)
+
2 e
–
}
X 5
10 e
–
+
16 H
+
(
aq
) +
2 MnO
4
–
(
aq
)
à
2 Mn
2+
(
aq
)
+
8 H
2
O (
l
)
10 Cl
–
(
aq
)
à
5 Cl
2
(
g
)
+
10 e
–
10 Cl
–
(
aq
)
+
16 H
+
(
aq
) +
2 MnO
4
–
(
aq
)
à
5 Cl
2
(
g
)
+
2 Mn
2+
(
aq
)
+
8 H
2
O (
l
)
b)
(4 pts) 10.0 g of KMnO
4
is dissolved in 250.0 g of an aqueous solution of NaCl that is 5.2%
NaCl by mass. What is the expected amount, in moles, of chlorine gas produced in the
reaction?
? )*+ O+
$
(PI*) LQ&R
&
) = 26. 6 S LQ&R
&
×
)*+ LQ&R
&
29J. 6M S
×
2 )*+ Q&R
&
–
2 )*+ LQ&R
&
×
9 )*+ O+
$
0 )*+ Q&R
&
–
= 6. 29J0 )*+ O+
$
? )*+ O+
$
(PI*) THO+)
= 096. 6 S ?*+& ×
9. 0 S THO+
266 S ?*+&
×
)*+ THO+
29J. FF S
×
2 )*+ O+
–
2 )*+ THO+
×
9 )*+ O+
$
26 )*+ O+
–
= 6. 2220 )*+ O+
$
NaCl is the limiting reagent and 0.1112 mol of chlorine gas will be formed.
Answer: __________________________________
c)
(3 pts) The chlorine gas produced in part (b) is collected over water at 26.0ºC, at a total
gas pressure of 0.9840 bar. If 1.37 L of gas is obtained, what is the percent yield of the
reaction in part (b)? The vapour pressure of water at 26.0ºC is 3.3639 kPa.
P
water
= 3.3639 kPa = 0.033639 bar
P
gas
= P
tot
– P
water
= 0.9840 bar – 0.033639 bar = 0.9504 bar
C >=U*IU>%VH+ =
&WD
B
=
(6. 2220 )*+)(6. 6JM2F9 K • GHI/)*+ • L)(044. 29 L)
6. 496F GHI
= 0. 42 K
% yield = (1.37 L / 2.91 L) x 100% = 47.1%
Answer: ________________________________
MnO
4
–
(
s
)
à
Mn
2+
(
aq
)
Cl
–
(
aq
)
à
Cl
2
(
g
)
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General Chemistry II Laboratory Manual, 2019 Revsion
39
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4
7
8
9.
10
11
12
13
Next >
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Help Center | Schoology Blog | PRIVACY POLICY | Terms of Use
Schoology © 2021
II
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