Chem. 1C Midterm 1
Version A
April 22, 2015
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incorrect or no units. Calculators are allowed. Cell phones may not be used for calculators.
On fundamental and short answer problems you must show your work in order to receive
credit for the problem. If your cell phone goes off during the exam you will have your
exam removed from you.
Fundamentals
(of 36 possible)
(
)+(
)=
Problem 1
(of 14 possible)
Problem 2
(of 20 possible)
Multiple Choice
(of 30 possible)
Midterm Total
(of 100 possible)
1
Fundamental Questions
Each of these fundamental chemistry questions is worth 6 points. You must show work to
get credit. Little to no partial credit will be rewarded. Make sure to include the correct
units on your answers.
1)
6 pts
Sketch the molecular orbital and label its type (σ or π; bonding or
antibonding) that would be formed when the following atomic orbitals
overlap.
π
+
+
2)
6 pts.
σ*
The graph shows how the vapor pressure of three liquids varies with
temperature.
What liquid is the most volatile?
Most Volatile: piperidine
What liquid is the least volatile?
What is the normal boiling point of each
liquid?
Least Volatile: orthoxylene
Ethylbenezene: 135˚C
Orthoxylene: 145˚C
Piperidine: 106˚C
☐ More
Suppose a beaker of orthoxylene is put
inside a sealed tank containing orthoxylene
gas at 132˚C and 320 torr. After ten
minutes, will there be more liquid in the
beaker, less liquid, or the same amount.
☒ Less
☐ The same
2
3)
6 pts
Carbon tetrachloride (CCl4) has a vapor pressure of 213 torr at 40.0˚C and
836 torr at 80˚C. What is the normal boiling point of CCl4?
 Pvap 1  H vap  1 1 
ln 

  
 Pvap 
R  T2 T1 

2 
H vap  1
1 
 213.torr 
ln 




J
 836.torr  8.3145 mol K  353K 313K 
J
H vap  31400 mol
Find the normal boiling point
J
1
1 
 213.torr  31400 mol
ln 
 


J
 760.torr  8.3145 mol K  T2 313K 
T2  350.K  77C
4)
5)
6 pts.
6 pts
List the kinds of intermolecular forces that are present in a pure sample of
the compound then circle the strongest intermolecular interaction for each
compound.
HCl
London, Dipole-Dipole
PCl3
London, Dipole-Dipole
CH3(CH2)100OH
London, Dipole-Dipole, H-Bonding
How are the local electron model and molecular theory similar? How are
they different? (75 words or less)
Both the local electron model and the molecular orbital theory are
based on the mixing of atomic orbitals that were determined from
quantum mechanics. The local electron model results from mixing
atomic orbitals that are on one atom. Molecular orbital theory mixes
orbitals from all of the atoms in the molecule.
6)
6 pts
Consider the phase diagram for iodine shown here
What is the normal boiling point for iodine? 184.4°C
What is the melting point for iodine at 1 atm?113.6°C
What state is present at room temperature and normal atmospheric
pressure? Solid
What state is present at 186°C and 1.0 atm? Gas
3
Short Answer Questions
Each of the following short answer questions are worth the noted points. Partial credit will
be given. You must show your work to get credit. Make sure to include proper units on
your answer.
Volume of a sphere = 43𝜋𝑟 3
1a) 5 pts.
Krypton crystallized with a face centered cubic unit cell of edge 559 pm.
What is the density of solid krypton in 𝑐𝑚𝑔 3 .
Determine the volume of the unit cell.
𝑉𝑐𝑒𝑙𝑙 = 𝑎3 = (559 × 10−10 𝑐𝑚)3 = 1.75 × 10−22 𝑐𝑚3
Determine the mass of krypton in unit cell
The unit cell has 4 Kr atoms
1𝑚𝑜𝑙 𝐾𝑟
83.798 𝑔
−22
4 𝐾𝑟 𝑎𝑡𝑜𝑚(6.022×10
𝑔
23 𝑎𝑡𝑜𝑚𝑠)(1 𝑚𝑜𝑙 𝐾𝑟) = 5.57 × 10
Determine the density of krypton
𝑑=
1b) 3 pts.
𝑚
𝑉
5.57×10−22 𝑔
= 1.75×10−22 𝑐𝑚3 = 3.18𝑐𝑚𝑔 3
What is the atomic radius of krypton in pm?
𝑎2 + 𝑎2 = (4𝑟)2
√2𝑎 √2(559 𝑝𝑚)
𝑟=
=
= 197 𝑝𝑚
4
4
1c) 5 pts.
What percent of the unit cell is empty space if each atom is treated as a
hard sphere?
Determine the volume that the atoms take up
Determine the volume of 1 Kr atom
1𝑚
𝑟𝐾𝑟 = 197 𝑝𝑚 (1012
) (100𝑐𝑚
) = 1.97 × 10−8 𝑐𝑚
1𝑚
𝑝𝑚
4
4
𝑉𝐾𝑟 = 3𝜋𝑟 3 = 3𝜋(1.97 × 10−8 )3 = 3.20 × 10−23 𝑐𝑚3
Determine the volume of 4 Kr atom
𝑉𝑓𝑖𝑙𝑙𝑒𝑑 = (4)(3.20 × 10−23 )𝑐𝑚3 = 1.28 × 10−22 𝑐𝑚3
Determine the percentage empty space
𝑉𝑒𝑚𝑝𝑡𝑦 = 𝑉𝑐𝑒𝑙𝑙 − 𝑉𝑓𝑖𝑙𝑙𝑒𝑑 = 1.75 × 10−22 𝑐𝑚3 − 1.28 × 10−22 𝑐𝑚3
𝑉𝑒𝑚𝑝𝑡𝑦 = 4.70 × 10−23 𝑐𝑚3
4.70 × 10−23 𝑐𝑚3
(
) 100% = 26.9%
1.75 × 10−22 𝑐𝑚3
4
2a) 6 pts
1) Draw the Lewis Structure of NO2-.
2) Identify the formal charges on each atom.
3) Identify the electronic arrangement of NO2-.
4) Identify the molecular shape of NO2-.
5) Identify the bond angles NO2-.
6) Identify if NO2- is polar or non-polar.
2) 0, 0, -1 and -1,0,0
3) Trigonal Planer
4) Bent
5) less than 120˚
6) Polar
2b)
8 pts
1) What is the hybridization of all of the atoms in POCl3? (Make sure to
minimize your formal charges.)
2) Determine the number of σ and π bonds in POCl3?
3) What orbital(s) overlap to make the bond(s) in this molecule? If there
are any lone pair(s) of electrons what type of orbitals are they in?
1) Cl = sp3, P = sp3, and O=sp2
2) 4 σ bonds and 1 π bonds
3) The sp3 hybridized orbital on the chlorine
overlaps with the sp3 hybridized orbital on the
phosphorus to form a σ bond (this is the same
for all Cl-P bonds). The sp2 hybridized orbital
on the oxygen overlaps with the sp3 hybridized
orbital on the phosphorus to form a sigma bond. The π bond between the
phosphorus and the oxygen is formed from the overlap of the p orbitals
oxygen and a d orbital on phosphorus. The lone pair electrons on the
chlorine atoms are in sp3 hybridized orbitals and the lone pair electrons on
the oxygen atom are in sp2 hybridized orbitals.
2c)
6 pts
1) What is the full electron configuration O22- (include core electrons)?
2) What is the bond order for O22-? What does this tell you about the
bond?
3) Is O22- diamagnetic or paramagnetic?
2
4
4
∗ )2 (𝜎 )2 (𝜎 ∗ )2
∗
1) (𝜎1𝑠 )2 (𝜎1𝑠
2𝑠
2𝑠 (𝜎2𝑝 ) (𝜋2𝑝 ) (𝜋2𝑝 )
2) b = ½ (N-N*)= ½(10-8) = 1 (Single Bond)
3) Diamagnetic
5
Multiple Choice Questions
Each of the following multiple choice questions are worth 5 points.
Your answers need to be filled in on your ParSCORE form.
Note: Your ParSCORE forms will not be returned to you, therefore,
for your records, you may want to mark your answers on this sheet.
On the ParSCORE you need to fill in your perm number, test
version, and name. Failure to do any of these things will result in
the loss of 1 point. Your perm number is placed and bubbled in
under the “ID number.” Do not skip boxes or put in a hyphen. In
addition, leave bubbles blank under any unused boxes. The version
number (A) is bubbled in under the “test form.”
1. Which of the following statements is true?
a. All antibonding MOs are higher in energy than the atomic orbitals of which they
are composed.
b. Electrons are never found in an antibonding MO.
c. Antibonding MOs have electron density mainly outside the space between the two
nuclei.
d. None of these statements is true.
e. Two of these statements are true.
2. Which of the following chemical species has the highest boiling point?
a. Li2O
b. NF3
c. O2
d. CH4
e. Ne
3. How many of the following substances can form hydrogen bonds?
CH3CH2OH
CH3OCH3
H3C-NH-CH3
CH3F
a. 1 of the molecules form H-bonds
b. none of the molecules form H-bonds
c. 3 of the molecules form H-bonds
d. All of the molecules form H-bonds
e. 2 of the molecules for H-bond
4. Which of the following is nonpolar?
a. SF2
b. H2O
c. ICl3
d. NCl3
e. None of the above are nonpolar
6
5. Which of the following has the shortest bond length? To answer this question you must
use MO theory?
a. NO+
b. NO2c. NO2+
d. NOe. NO
6. Which of the following statements is correct?
a.  bonds have electron density on the internuclear axis.
b.  bonds result from the head-to-head overlap of atomic orbitals.
c. A triple bond is composed of two  bonds and one  bond.
d. Free rotation may occur about a double bond.
e. More than one of these statements are correct.
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