Chem 127, Final Exam
December 14, 2001
Name
I. (55 points) This part of the final corresponds to Exam I. It covers the material in
Chapters 1, 2 and 3.
A. (8 points) Fill in the empty boxes with the appropriate symbol, number, word or charge.
Nuclear symbol
40
Ca
Protons
Neutrons
Ag +
47
20
46
(name of subatomic
particle)
Mass Number
107
Atomic Number
Net Charge
0
1
Chem 127, Final Exam
December 14, 2001
Name
B. (8 points) Determine whether the statements given below are true or false. Write Y if
the statement is true, and N if the statement is false in the blanks provided. Do not
use T or F.
1. All the isotopes of an element have the same number of protons but varying
numbers of neutrons.
2. The horizontal rows in a periodic table are referred to as ”periods”.
3. Crystals of iodine can be classified as a heterogeneous mixture.
4. The mass (in grams) of one mole of nitrogen molecules is 14.01.
C. (16 points) Write the formulas or names of the following compounds.
1. Sulfur dioxide
2. Tin(II) nitrate
3. Perchloric acid
4. ammonia
5. CH4
6. AlBr3
7. Fe2 (SO3 )3
8. IBr3
2
Chem 127, Final Exam
December 14, 2001
Name
D. (8 points) Consider acetic acid C2 H4 O2
1. What is its molar mass in grams?
2. What is its simplest formula?
3. When acetic acid is burned in air, carbon dioxide and water are produced. Balance the equation for this reaction by writing the appropriate coefficients on the
blanks provided.
C2 H4 O2 () +
O2 (g) →
CO2 (g) +
H2 O ()
E. (6 points) Consider ethyl alcohol, C2 H6 O, (M = 46.1 g/mol).
1. How many grams of hydrogen can be obtained from 138 g of ethyl alcohol?
4. What is the mass percent of carbon in ethyl alcohol?
3
Chem 127, Final Exam
December 14, 2001
Name
F. (9 points) Consider the following balanced equation:
2 Sb (s) + 3 F2 (g) → 2 SbF3 (s)
To produce SbF3 (M = 178.75 g/mol), 5.00 g of Sb (M = 121.75 g/mol) and 5.00 g
of F2 (M = 38.00 g/mol) are mixed together.
1. How many moles of Sb are present before reaction?
2. How many moles of F2 are present before reaction?
3. What is the limiting reactant?
4. Assuming 100% yield how many grams of SbF3 are produced after reaction is
complete?
4
Chem 127, Final Exam
December 14, 2001
Name
II. (70 points) This part of the final corresponds to Exam II. It covers the material in
Chapters 4 and 5.
A. (8 points) Write your answers to the following questions on the space provided. You
may do your calculations on the scratch paper provided. These will not be graded.
Consider 200.0 mL of 0.300 M FeCl3 . The next 4 questions refer to this solution.
1. How many moles of chloride ions are present in this solution?
2. When NaOH reacts with FeCl3 , the following reaction occurs:
Fe3+ (aq) + 3 OH− (aq) → Fe(OH)3 (s)
How many moles of NaOH are required to completely react with
this solution of FeCl3 ?
3. How many mL of this solution are required to prepare 1.00 L
of a 0.0100 M solution of FeCl3 ?
4. When an oxidizing agent is added to the FeCl3 solution, chlorate
ions are formed.
−
Cl− (aq) → ClO−
3 (aq) + ? e
How many electrons are lost in this oxidation?
B. (12 points) Write the formula(s) of the product(s) obtained by mixing aqueous 0.1M
solutions of the following compounds. Write NR if there is no reaction Do not include
spectator ions.
1. HCl and KOH
2. H2 SO4 and Ca(NO3 )2
3. NaOH and ZnCO3
4. HNO2 and Sr(OH)2
5. NH3 and HClO4
5
Chem 127, Final Exam
December 14, 2001
Name
C. (10 points) Balance the following equation in acid medium. Do your work on the
scratch paper provided. Answer the following questions about the balanced equation
in the blanks provided.
2−
(aq)
Al3+ (aq) + SO2−
3 (aq) → Al (s) + SO4
1. What is the oxidation number for sulfur in SO2−
3 ?
2. What is the reducing agent?
3. How many electrons are gained in the reduction half-reaction?
4. How many moles of H+ ions are present in the balanced redox
equation?
5. What is the coefficient of the sulfate ion in the balanced redox
equation?
D. (4 points) Aluminum nitrate (Al(NO3 )3 ) reacts with NaOH to form a precipitate according to the following balanced equation.
Al3+ (aq) + 3 OH− (aq) → Al(OH)3 (s)
Assuming 100% yield, how many mL of 0.500 M NaOH are required to produce 1.500
g of Al(OH)3 (M = 78.00 g/mol)?
6
Chem 127, Final Exam
December 14, 2001
Name
E. (6 points) A sample of an alloy made up of zinc and a nonreactive metal is analyzed
by treatment with nitrate ion in basic solution. The following is a balanced equation
for the redox reaction that occurs.
4 Zn (s) + 7 OH− (aq) + NO3− (aq) + 6 H2 O → 4 Zn(OH)2−
4 (aq) + NH3 (aq)
If 25.00 mL of 0.371 M sodium nitrate is used to furnish the nitrate ions, what is the
minimum volume of 0.177 M barium hydroxide needed to furnish enough hydroxide
ions? Assume 100% yield.
F. (10 points) Consider 3 sealed tanks all at the same temperature, pressure and volume.
— Tank A contains SO2 gas
— Tank B contains O2 gas
— Tank C contains CH4 gas
Fill in the blanks on the left, using LT (for is less than) , GT (for is greater than) , EQ
(for is equal to) , or MI (for more information required).
1. The mass of SO2 in Tank A
the mass of O2 in Tank B.
2. The kinetic energy of CH4 in Tank C
the kinetic energy of SO2 in Tank A.
3. It takes 20 seconds for all of the O2 gas in Tank B to effuse out of a pinhole
in the tank. The time it takes for all of the SO2 to effuse out of Tank A from
40 seconds.
an identical pinhole
4. The density of O2 in Tank B
the density of CH4 in Tank C.
5. The temperature in Tank A is increased from 150 K to 300K. The temperature
half the pressure in
in Tank B is kept at 150 K. The pressure in Tank A is
Tank B.
7
Chem 127, Final Exam
December 14, 2001
Name
G. (15 points) Write your answers to the problems in the blanks provided. Do your
calculations on scratch paper. Only the answers on the blanks will be considered.
1. A 0.50 L sample of gas in a closed container at 0.50 atm is
compressed to 0.10 L at constant temperature. What is the pressure of the gas after compression?
2. Hydrogen gas is collected over water at 758 mm Hg. The vapor
pressure of water is 22 mm Hg. What is the pressure of the dry
gas in mm Hg?
3. Neon gas effuses out of a pinhole at the rate of 200 mL/s. At the
same temperature, what is the rate at which another gas with a
molar mass of 80 g/mol effuses?
4. A flask contains 10.0 g of Ar and 3.00 g of He. The total pressure
is 1.00 atm. What is the partial pressure of Ar?
5. A 4.00 L flask has 38.0 g of fluorine gas at 300 K. What is the
pressure of the gas in the flask?
H. (5 points) Nitric acid can be prepared by bubbling dinitrogen pentoxide (N2 O5 ) into
water according to the following reaction.
N2 O5 (g) + H2 O → 2 H+ (aq) + 2 NO3− (aq)
1.50 L of N2 O5 at 25◦ C and 1.00 atm is bubbled into water. The total volume of the
aqueous solution of nitric acid obtained is 437 mL. Assuming 100% yield, what is the
molarity of the nitric acid solution obtained?
8
Chem 127, Final Exam
December 14, 2001
Name
III. (70 points) This part of the final corresponds to Exam III. It covers the material in
Chapters 6, 7, and 8.
A. (20 points) Write your answers in the blanks provided.
1. How many electrons can an atom have with quantum numbers n = 3, = 2,
and ms = 1/2?
2. How many d electrons are in the ground state of Zn?
3. How many d electrons are in the ground state of Zn2+ ?
4. How many unpaired electrons are there in an atom of phosphorus?
5. How many unpaired electrons are there in an atom of chlorine?
6. What is the symbol of the element with the smallest radius in Group 16?
7. What is the symbol of the element with the highest first ionization energy
in Period 4?
8. What is the symbol of the element with a +4 ion that has the abbreviated
electron configuration: [Kr] 4d6 ?
9. What is the symbol of the most electronegative element in Group 17?
10. Write the orbital diagram for oxygen in the ground state by putting up and down arrows
in the empty orbitals provided below. Label the orbitals that you use.
(
) (
) (
) (
) (
) (
9
) (
) (
) (
)
Chem 127, Final Exam
December 14, 2001
Name
B. (6 points) What wavelength is associated with a transition from n = 10 to n = 5?
In this transition is energy absorbed or given off?
C. (19 points) Write your answers on the blanks provided.
1. Predict the molecular geometry of NH3 .
2. Predict the molecular geometry of IF3 .
3. What is the hybridization of C in HCN?
4. How many pi bonds does N2 have?
5. How many sigma bonds does CO2 have?
Consider 2 possible Lewis structures for SeO3 (labeled A and B) given below.
..
..
..
..
:O
–
Se
–
O:
:O
=
Se
=
O:
..
..
:O:
:O:
(A)
(B)
8. How many different resonance structures can be written for
for Structure A? (Count the one given as the first one.)
9. Which structure gives the minimum formal charge for all atoms?
10
Chem 127, Final Exam
December 14, 2001
Name
D. (6 points) Consider the following molecules whose Lewis structure is given. In the
box provided, write P if the molecule is polar, and NP if the molecule is nonpolar.
E. (6 points) Given the following data:
∆ Hfus for benzene (C6 H6 ) = 9.84 kJ/mol
∆ Hvap for water = 40.7 kJ/mol
1. Which process absorbs more heat, freezing 5.00 mol of benzene or vaporizing
1.00 mol of water?
2. How many joules of energy does your chosen process require?
11
Chem 127, Final Exam
December 14, 2001
Name
F. (7 points) Five cent coins (nickels) weigh 5.0 g. After 30 cents worth of nickels at
100◦ C are placed in a coffee cup calorimeter containing 50.0 g of water at 22◦ C, the
temperature of the water is 30.0◦ C. Specific heat of water = 4.18 J/g◦ C
1. How many joules of heat are absorbed by the water?
2. What is the specific heat of nickel?
G. (6 points) Given the following thermodynamic equations:
∆H◦ = – 571.6 kJ
2 H2 (g) + O2 (g) → 2 H2 O ()
N2 O5 (g) + H2 O () → 2 HNO3 ()
N2 (g) + 3 O2 (g) + H2 (g) → 2 HNO3 ()
∆H◦ = – 73.7 kJ
∆H◦ = – 348.2 kJ
Use Hess’s Law to calculate ∆H◦ for the reaction
N2 (g) + 5/2 O2 (g) → N2 O5 (g)
Write the ∆H◦ values that you sum to find your answer on the line below.
+
+
=
12
Chem 127, Final Exam
December 14, 2001
Name
IV. (55 points) This part of the final corresponds to Chapter 9.
A. (14 points) Consider the phase diagram for CCl4 given below. Answer the questions
about the diagram by writing your answers on the blanks provided.
1. What point (not including the triple point) represents an equilibrium
between the solid and the vapor phase?
2. What is CCl4 at point G called?
3. Does the boiling point increase as pressure above the liquid is
decreased? (Yes or No)
4. What point represents CCl4 only in the gas phase?
5. Does the melting point increase as pressure is applied to the solid?
(Yes or No)
6. Is sublimation of CCl4 impossible at any pressure? (Yes or No)
7. For a specific temperature above point E, the density of the liquid
phase is larger than the density of the solid phase. (Yes or No)
13
Chem 127, Final Exam
December 14, 2001
Name
.
B. (12 points) Answer the following questions.
1. The important intermolecular force in I2 crystal is: Circle one
metallic
network covalent
ionic
dispersion
dipole
hydrogen bonding
2. Write all the intermolecular forces present in both CH3 Cl and CH3 I.
3. CH3 Cl has a lower boiling point than CH3 I. What intermolecular force accounts
for this phenomenon?
Consider the following vapor pressure diagram.
4. Which liquid has a higher boiling point?
5. Which liquid would evaporate more quickly?
14
Chem 127, Final Exam
December 14, 2001
Name
C. (18 points) Consider chloroform (CHCl3 ). It has the following properties:
— melting point = – 63◦ C
— vapor pressure at 25◦ C = 213 mm Hg
— ∆Hvap = 29.2 kJ/mol
1. A flask with a volume of 2.00 L is sealed at 25◦ C after 0.0100 mol of CHCl are
added. What is the pressure in the flask?
2. What phase(s) of chloroform is/are present in the flask described in (1)?
3. What is the maximum volume that the flask described in (1) can have so that both
phases of CHCl3 are present?
4. What is the vapor pressure of chloroform at 45◦ C?
15
Chem 127, Final Exam
December 14, 2001
Name
D. (5 points) An element X crystallizes with a simple cubic cell. The volume of a cell is
0.0106 nm3 . What is the radius of an atom of X?
E. (9 points) Consider the following substances (Lewis structures may be necessary in
some cases.):
CO2
HF
KO2
K
SO2
diamond
Match the substance(s) with the following properties. Note that you can write more
than one answer on the blank and that you may use the substance as an answer more
than once.
1. is an ionic compound.
2. has hydrogen bonding.
3. has dipole forces
4. has dispersion forces.
5. conducts electricity well in the solid.
6. is network covalent.
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Chem 127, Final Exam
December 14, 2001
Name
BONUS (15 points) All or nothing.
The bonus should be done only after you have completed the main part of this exam and
checked your work for errors. The time allotted for this exam does not include time for the
bonus. (SHOW ALL WORK! Lucky guesses will not be considered.)
When magnesium metal burns in air, it reacts with oxygen to form magnesium oxide and
with nitrogen to form magnesium nitride. Magnesium nitride reacts with water to form
magnesium oxide and ammonia gas. In a particular experiment, a piece of magnesium
was burned in air to give 0.425 g of a mixture of magnesium oxide and magnesium nitride.
Water was added and the mixture was heated until 0.441 g of dry MgO remained. What is
the mass percent of magnesium nitride in the mixture of magnesium oxide and magnesium
nitride?
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