Chemistry 1303.003
Exam 3 (100 points)
Name
December 1, 2016
On my honor, I have neither given nor received unauthorized aid on this exam.
Signed
Date
- 3 points for not following these directions → Circle ONLY the LETTER of the correct answer.
1.
(2 points) Barium chloride, BaCl2, melts at 962 °C and is very hard. The liquid conducts electricity very well.
a.
b.
c.
covalent network
molecular
metallic
d.
e.
f.
ionic
amorphous
none of these
2. (2 points) Osmium tetroxide, OsO4, is a soft crystal that melts at 40 °C. The liquid does not conduct electricity. The most
likely crystal type for OsO4 is
a. covalent network
d. ionic
b. molecular
e. amorphous
c. metallic
f.
none of these
3.
(2 points) The
meniscus observed when water is placed in a narrow glass tube is
and is caused by
.
a.
b.
c.
4.
(4 points) Arrange
d.
e.
f.
curved downward
curved downward
none of these
; viscosity
; adhesion
the following in order of increasing boiling point: MgCl2, CH3Cl, CH3OH, CH4
a.
MgCl2 < CH3Cl < CH3OH < CH4
d.
b.
CH4 < CH3Cl < CH3OH < MgCl2
MgCl2 < CH3OH < CH3Cl < CH4
e.
CH4 < CH3OH < CH3Cl < MgCl2
CH4 < CH3Cl < MgCl2 < CH3OH
f.
MgCl2 < CH3OH < CH4 < CH3Cl
c.
5.
curved upward ; viscosity
curved upward ; cohesion
curved upward ; adhesion
(3 points) Which
a.
b.
c.
of the following molecules (is)are polar. [More than one answer is possible here.]
BrF5
PH3
XeF4
d.
e.
f.
SeF2
SO3
SbF5
6. (3 points) Which of the following will have the largest surface tension at a given temperature.
a.
b.
c.
CF4
CH2F2
CH3F
d.
e.
f.
CH3CH2OH
CH3OH
H2O
7. (3 points) The molar heats of sublimation and fusion of iodine are 62.3 kJ/mole and 15.3 kJ/mole, respectively.
Estimate the molar heat of vaporization of liquid iodine.
a.
1576 kJ/mol
d.
31.7 kJ/mol
b.
77.6 kJ/mol
e.
4.1 kJ/mol
c.
47.0 kJ/mol
f.
none of these
2
8.
(3 points) Given
the following bond energies, estimate the enthalpy of combustion of one mole of ethylene (∆H).
C2H4 + 3 O2 → 2 CO2 + 2 H2O
BE (CH) = 414 kJ
BE (CC) = 347 kJ
a.
b.
c.
9.
BE (C≡O) = 1074 kJ
BE (C=O) = 799 kJ
+ 1255 kJ
-335 kJ
+335 kJ
(6 points)
BE (O=O) = 499 kJ
BE (OH) = 460 kJ
d.
e.
f.
BE (C=C) = 620 kJ
-1263 kJ
+1263 kJ
None of these
Identify each of the following by placing the correct letter in the blank.
normal freezing temperature
liquid-gas equilibrium
sublimation point
10. (10 points) Use Molecular Orbital Theory as it applies to simple diatomic molecules and ions to answer the
following questions. A rough, unlabeled sketch is provided for your assistance
a. Circle any of the following molecules that are
paramagnetic.
Ne2
O2
B2
C2
N2
Li2
2p
2p
b. The molecule CO has _______ unpaired electron(s) in
the _________ energy level.
c. The bond order of the cation CO– is _______________.
2s
d. Which has the longest bond distance? (circle one)
–
O2
O2
O2+
2s
σ2s
11. (6 points) The element tungsten (W), currently popular for rings and other jewelry, crystallizes in a body
centered cubic unit cell. The density of tungsten is 19.3 g/cm3. Determine the edge length of the unit cell of
tungsten in picometers. SHOW ALL WORK.
3
12. Consider the simple organic compound HNCHCCH where the atoms are connected by some type of bond at the
dotted line as shown in the box on the left.
H
H
N
C
a
C
b
C
c
H
a.
(2 points)
In the box on the right above, draw the complete the Lewis electron dot formula.
c.
(3 points)
What is the hybridization at each of the atoms?
N ____________
C(labeled a) ___________
C(labeled b) __________
d.
(1 point)
e.
(3 points)
f.
(8 points) Describe the bonding in HNCHCCH using Valence Bond concepts (i.e., hybrid atomic
orbitals, etc.). Draw and clearly label one or more pictures to show the types of orbitals that you are
using to form the various σ and/or π bonds.
The Ca—Cb— Cc bond angle is about
degrees.
Clearly sketch the 3-D structure of the molecule, including the relative orientation of the C–H,
C–C, and C–N bonds.
13. (5 points) Write complete Lewis electron dot formulas for CO32-, including formal charges. Show resonance
forms if appropriate.
4
14. (7 points) Apply VSEPR concepts to the following ions. In each case, draw a clear 3-D structure and give a
description of the shape (i.e., tetrahedral, trigonal planer, etc.). Also, state the hybridization of the central atom
in each case.
–
IF2
SeBr3+
H2SO3
15. (6 points) Draw three different but reasonable 3-D structures for the molecule F3PCl2. Indicate whether each
one is polar or non-polar.
16. a. (10 points) Write complete Lewis electron dot formulas for all five of the molecules and ions (don't forget
O22-) in the following reactions. Include formal charges and/or resonance forms where necessary.
H3B
+
CO
H3BCO
O2-
[H3BCO2]2-
Related to the question 9 above, the C–O bond order is ____________ in H3BCO and
____________ in [H3BCO2]2-.
b. (4 points)
17. (2 points) Consider the compounds in problems 13-16. The one(s) that are best described as having delocalized
orbitals is(are)
.
18. (5 points) The specific heat of liquid ethanol, C2H5OH(l), is 2.46 J/g·°C and the heat of vaporization is 39.3
kJ/mol. The boiling point of ethanol is 78.3 °C. What amount of enthalpy is required to heat 50.0 g of liquid
ethanol from 13.0 °C to ethanol vapor at 78.3 °C? SHOW ALL WORK to clearly justify your answer.
Chemistry 1303.003
Exam 3 (100 points)
Name
December 1, 2016
On my honor, I have neither given nor received unauthorized aid on this exam.
Signed
Date
- 3 points for not following these directions → Circle ONLY the LETTER of the correct answer.
1.
(2 points) Barium chloride, BaCl2, melts at 962 °C and is very hard. The liquid conducts electricity very well.
a.
b.
c.
covalent network
molecular
metallic
d.
e.
f.
ionic
amorphous
none of these
2. (2 points) Osmium tetroxide, OsO4, is a soft crystal that melts at 40 °C. The liquid does not conduct electricity. The most
likely crystal type for OsO4 is
a. covalent network
d. ionic
b. molecular
e. amorphous
c. metallic
f.
none of these
3.
(2 points) The
meniscus observed when water is placed in a narrow glass tube is
and is caused by
.
a.
b.
c.
4.
(4 points) Arrange
d.
e.
f.
curved downward
curved downward
none of these
; viscosity
; adhesion
the following in order of increasing boiling point: MgCl2, CH3Cl, CH3OH, CH4
a.
MgCl2 < CH3Cl < CH3OH < CH4
d.
b.
CH4 < CH3Cl < CH3OH < MgCl2
MgCl2 < CH3OH < CH3Cl < CH4
e.
CH4 < CH3OH < CH3Cl < MgCl2
CH4 < CH3Cl < MgCl2 < CH3OH
f.
MgCl2 < CH3OH < CH4 < CH3Cl
c.
5.
curved upward ; viscosity
curved upward ; cohesion
curved upward ; adhesion
(3 points) Which
a.
b.
c.
of the following molecules (is)are polar. [More than one answer is possible here.]
BrF5
PH3
XeF4
d.
e.
f.
SeF2
SO3
SbF5
6. (3 points) Which of the following will have the largest surface tension at a given temperature.
a.
b.
c.
CF4
CH2F2
CH3F
d.
e.
f.
CH3CH2OH
CH3OH
H2O
7. (3 points) The molar heats of sublimation and fusion of iodine are 62.3 kJ/mole and 15.3 kJ/mole, respectively.
Estimate the molar heat of vaporization of liquid iodine.
a.
1576 kJ/mol
d.
31.7 kJ/mol
b.
77.6 kJ/mol
e.
4.1 kJ/mol
c.
47.0 kJ/mol
f.
none of these
2
8.
(3 points) Given
the following bond energies, estimate the enthalpy of combustion of one mole of ethylene (∆H).
C2H4 + 3 O2 → 2 CO2 + 2 H2O
BE (CH) = 414 kJ
BE (CC) = 347 kJ
a.
b.
c.
9.
BE (C≡O) = 1074 kJ
BE (C=O) = 799 kJ
+ 1255 kJ
-335 kJ
+335 kJ
(6 points)
BE (O=O) = 499 kJ
BE (OH) = 460 kJ
d.
e.
f.
BE (C=C) = 620 kJ
-1263 kJ
+1263 kJ
None of these
Identify each of the following by placing the correct letter in the blank.
normal freezing temperature
liquid-gas equilibrium
sublimation point
10. (10 points) Use Molecular Orbital Theory as it applies to simple diatomic molecules and ions to answer the
following questions. A rough, unlabeled sketch is provided for your assistance
a. Circle any of the following molecules that are
paramagnetic.
Ne2
O2
B2
C2
N2
Li2
2p
2p
b. The molecule CO has _______ unpaired electron(s) in
the _________ energy level.
c. The bond order of the cation CO– is _______________.
2s
d. Which has the longest bond distance? (circle one)
–
O2
O2
O2+
2s
σ2s
11. (6 points) The element tungsten (W), currently popular for rings and other jewelry, crystallizes in a body
centered cubic unit cell. The density of tungsten is 19.3 g/cm3. Determine the edge length of the unit cell of
tungsten in picometers. SHOW ALL WORK.
3
12. Consider the simple organic compound HNCHCCH where the atoms are connected by some type of bond at the
dotted line as shown in the box on the left.
H
H
N
C
a
C
b
C
c
H
a.
(2 points)
In the box on the right above, draw the complete the Lewis electron dot formula.
c.
(3 points)
What is the hybridization at each of the atoms?
N ____________
C(labeled a) ___________
C(labeled b) __________
d.
(1 point)
e.
(3 points)
f.
(8 points) Describe the bonding in HNCHCCH using Valence Bond concepts (i.e., hybrid atomic
orbitals, etc.). Draw and clearly label one or more pictures to show the types of orbitals that you are
using to form the various σ and/or π bonds.
The Ca—Cb— Cc bond angle is about
degrees.
Clearly sketch the 3-D structure of the molecule, including the relative orientation of the C–H,
C–C, and C–N bonds.
13. (5 points) Write complete Lewis electron dot formulas for CO32-, including formal charges. Show resonance
forms if appropriate.
4
14. (7 points) Apply VSEPR concepts to the following ions. In each case, draw a clear 3-D structure and give a
description of the shape (i.e., tetrahedral, trigonal planer, etc.). Also, state the hybridization of the central atom
in each case.
–
IF2
SeBr3+
H2SO3
15. (6 points) Draw three different but reasonable 3-D structures for the molecule F3PCl2. Indicate whether each
one is polar or non-polar.
16. a. (10 points) Write complete Lewis electron dot formulas for all five of the molecules and ions (don't forget
O22-) in the following reactions. Include formal charges and/or resonance forms where necessary.
H3B
+
CO
H3BCO
O2-
[H3BCO2]2-
Related to the question 9 above, the C–O bond order is ____________ in H3BCO and
____________ in [H3BCO2]2-.
b. (4 points)
17. (2 points) Consider the compounds in problems 13-16. The one(s) that are best described as having delocalized
orbitals is(are)
.
18. (5 points) The specific heat of liquid ethanol, C2H5OH(l), is 2.46 J/g·°C and the heat of vaporization is 39.3
kJ/mol. The boiling point of ethanol is 78.3 °C. What amount of enthalpy is required to heat 50.0 g of liquid
ethanol from 13.0 °C to ethanol vapor at 78.3 °C? SHOW ALL WORK to clearly justify your answer.