CHEMISTRY 101
Hour Exam III
December 7, 2006
Adams/Le
Name ___________KEY____________________
Signature ________________________________
T.A./Section ______________________________________
“Success means having the courage, the determination, and the will to
become the person you believe you were meant to be.” George Sheehan
This exam contains 17 questions on 6 numbered pages. Check now to make sure you have a
complete exam. You have one hour and fifteen minutes to complete the exam. Determine
the best answer to the first 15 questions and enter these on the special answer sheet. Also,
circle your responses in this exam booklet. Show all of your work and provide complete
answers to questions 16 and 17.
1-15
(30 pts.)
_________
16
(12 pts.)
_________
17
(18 pts.)
_________
(60 pts)
_________
Total
Useful Information:
1.000 L = 1000.0 mL
Always assume ideal behavior for gases (unless explicitly told otherwise).
PV = nRT
R = 0.08206 L·atm/mol·K
K = °C + 273
STP = standard temperature and pressure = 0°C and 1.00 atm
NA = 6.022 x 1023
Solubility Rules:
1. Most nitrate salts are soluble.
2. Most salts of sodium, potassium, and ammonium cations are soluble.
3. Most chloride salts are soluble. Exceptions: silver(I), lead(II), and mercury(I) chloride.
4. Most sulfate salts are soluble. Exceptions: calcium, barium, and lead (II) sulfate.
5. Most hydroxide salts can be considered insoluble. Soluble ones: sodium, potassium, and
calcium hydroxide.
6. Consider sulfide, carbonate, and phosphate salts to be insoluble. Soluble ones: sodium
and potassium.
CHEMISTRY 101
Hour Exam III
Fall 2006
Page No. 1
1. Which scientist is still credited today for determining how an electron moves around the
nucleus of an atom?
a)
b)
c)
d)
e)
Ernest Rutherford
J.J. Thomson
John Dalton
Niels Bohr
No scientist is credited for this discovery because we do not know exactly how
electrons travel in an atom.
2. Which of the following elements has the largest ionization energy?
a) P
b) Al
c) Cl
d) Ba
e) K
3. Rank the following from smallest to largest atomic radius: Ar, S2–, Ca2+, K+, Cl–.
a)
b)
c)
d)
e)
Ca2+ < K+ < Ar < Cl– < S2–
Ar < K+ < Ca2+ < S2– < Cl–
Ar < Cl– < S2– < Ca2+ < K+
K+ < Ca2+ < Ar < S2– < Cl–
S2– < Cl– < Ar < K+ < Ca2+
4. For the titration of 3.00 M hydrochloric acid with 2.00 M sodium hydroxide, what volume of
sodium hydroxide would be required to react with 1.00 L of hydrochloric acid to reach the
endpoint?
a) 0.667 L
b) 1.50 L
c) 2.00 L
d) 3.00 L
e) 6.00 L
--------------------------------------------------------------------------------------------------------------------Consider the following compounds to answer questions 5 – 8.
NH4+
HCN
NO2–
SF6
5. How many of the compounds above contain a central atom that obeys the octet rule?
a) 0
b) 1
c) 2
d) 3
e) 4
6. How many of the compounds above exhibit resonance?
a) 0
b) 1
c) 2
d) 3
7. Which compound exhibits London dispersion forces?
a)
b)
c)
d)
e)
HCN
NH4+
SF6
NO2–
All of the above exhibit London dispersion forces.
e) 4
CHEMISTRY 101
Hour Exam III
Fall 2006
Page No. 2
8. Which compound has bond angles of 120° around the central atom?
a)
b)
c)
d)
e)
HCN
NH4+
SF6
NO2–
At least two of the above have bond angles of 120°.
---------------------------------------------------------------------------------------------------------------9. How many of the following statements are true concerning an electron in its ground state?
I. The electron must be in its lowest-energy state.
II. Energy must be applied to the electron in order to excite it.
III. The electron must be located on the nucleus of an atom.
IV. The electron can release energy to obtain a lower ground state.
a) 0
b) 1
c) 2
d) 3
e) 4
10. Liquid water turns to ice. Is this process endothermic or exothermic? Choose the best
answer.
a) endothermic; The water absorbed heat and got colder, therefore forming ice.
b) endothermic; Energy in the form of heat was given off by the water to become colder
and form ice.
c) exothermic; The water released energy, slowing the water molecules down to form
solid ice.
d) exothermic; Heat was absorbed by the water, moving its molecules faster to condense
on an object and form ice.
e) neither endothermic nor exothermic; There was no energy transfer in or out of the
water to form ice.
11. Which of the following compounds has the highest boiling point?
a) H2O
b) MgCl2
c) CO2
d) CH4
e) SF4
d) Sr–O
e) Fe–P
12. Choose the bond that is the most polar.
a) N–N
b) C–O
c) P–S
CHEMISTRY 101
Hour Exam III
Fall 2006
Page No. 3
13. When an electron is excited in an atom or ion
a) the electron moves further from the nucleus.
b) only specific quantities of energy are released in order for the electron to return to its
ground state.
c) white light is never observed when the electron returns to its ground state.
d) the electron is only excited to certain energy levels.
e) All of the above statements are true when an electron is excited.
14. Which atom or ion has the smallest radius?
a) O2+
b) O+
c) O
d) O–
e) O2–
15. Which of the following solutes will generally not dissolve in the specified solvent?
Choose the best answer. (Assume all of the compounds are in the liquid state.)
a)
b)
c)
d)
e)
CCl4 mixed with water (H2O)
NH3 mixed with water (H2O)
CH3OH mixed with water (H2O)
N2 mixed with methane (CH4)
CO2 mixed with methane (CH4)
CHEMISTRY 101
Hour Exam III
4 points
Fall 2006
Page No. 4
16. a) State whether each electron configuration is possible or not possible. (The
elements could be in a ground state or excited state.) Justify each answer. For
those that are possible, state what the element is. For those that are not possible,
give a corrected electron configuration that is possible.
1s22s22p7
Not Possible; There can only be 6 electrons in the p orbitals. One
corrected electron configuration is 1s22s22p63s1
[Ne] 3s23p3
Possible; the element is phosphorus
1s22s22p62d7
Not Possible; The d orbitals do not exist until the 3rd energy level. One
corrected electron configuration is 1s22s22p63s23p5
1s22s12p3
Possible; the element is carbon in the excited state
3 points
b) Fill in the energy level diagram for the ground-state of nitrogen. Justify your
placement of electrons in the energy level diagram.
The electrons fill closest to the nucleus first (lower in
energy). In the 2p orbital, the electrons spread out
between the three different orientations because the
electrons have negative charges so they repel
each other.
5 points
c) If nitrogen forms bonds with potassium, what type of bonds are these (ionic, polar
covalent, or covalent)? What is the resultant electron configuration for each
element when these bonds occur? Are these bonds polar or nonpolar? Why?
The bonds are ionic.
K+ = 1s22s22p63s23p6
N3– = 1s22s22p6
These bonds are polar because there is a large difference in
electronegativity betweem potassium and nitrogen which creates an
unequal electron distribution in the bond.
CHEMISTRY 101
Hour Exam III
Fall 2006
Page No. 5
17. a) Fill in the table below with the appropriate information. For the Lewis structures, be
sure to make your drawings clear and make your dots visible (or else you will not
receive credit). In addition, make sure you give a brief justification as to why each
molecule is polar or nonpolar overall.
10 points
Formula
XeO4
Lewis Structure
O
O
Geometry
Molecular
Shape
Polar or Nonpolar?
(with justification)
tetrahedral
tetrahedral
Non-polar (equal electron
distribution throughout; dipoles
cancel)
tetrahedral
trigonal
pyramid
Polar (uneven electron
distribution; dipoles do not cancel;
more electron density towards
fluorines)
trigonal
bipyramid
T-shape
Polar (uneven electron
distribution; dipoles do not cancel;
more electron density towards
chlorines)
trigonal
planar
trigonal
planar
Non-polar (equal electron
distribution throughout; dipoles
cancel)
square planar
Non-polar (equal electron
distribution throughout; dipoles
cancel)
Xe
O
O
N
NF3
F
F
F
Cl
I
Cl
ICl3
Cl
H
BH3
B
H
H
Br
KrBr4
Br
Kr
Br
Br
octahedral
CHEMISTRY 101
Hour Exam III
Fall 2006
Page No. 6
b) Give an example of a linear molecule that is polar. Explain why it is polar even
though the bond angle is 180°, along with a complete Lewis structure of your
molecule.
Answers will vary. Make sure it is a valid Lewis structure that is actually
linear and polar. The molecule is polar because there is uneven electron
distribution throughout (the dipole(s) do not cancel due to the differences
in electronegativity between the atoms).
4 points
c) One Lewis structure of CCl4 is
Cl
Cl
C
Cl
Cl
According to the VSEPR model, the actual bond angles around the central atom are
109.5° (meaning CCl4 is tetrahedral in shape). Why aren’t the bond angles 90° as
indicated in the Lewis structure above? (In other words, why isn’t CCl4 square planar
in shape?)
4 points
Electrons repel each other so the atoms arrange themselves around the
carbon to maximum the distance between the chlorine atoms (where the
electron pairs are) and minimize repulsions.