Version 165 – Exam 3 – mccord – (52125)
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mccord - ch301
— Exam 3 —
Dat Acid
7-9pm Nov 5, 2013
1
Viscosity = measure of a liquid’s resistance
to flow. Generally as liquids get warmer
they flow more readily (think of molasses or
honey), so viscosity decreases as temperature
increases.
003 3.0 points
Which of the following molecules can form
hydrogen bonds with itself?
1. CH3 CN
BUR 106
2pm class only - 52125
2. CF3 CH3
3. all three molecules can form hydrogen
bonds
001 3.0 points
Which of the following best describes where
the highest electron density is for a π-bond
between two atoms in a molecule?
1. above and below the axis but not on the
bond axis correct
2. directly on the axis and around the axis
3. directly on the on the bond axis
4. either above or below the axis but not
both
5. distributed evenly throughout the entire
molecule
Explanation:
π-bonds are formed by the side-to-side overlap of p orbitals which results in electron density above and below the bond axis but not
on the axis. σ-bonds have their densities on
the bond axis.
002 2.0 points
Viscosity usually increases with increasing
temperature.
1. True
2. False correct
Explanation:
4. CH3 CH2 OH correct
Explanation:
In order to form hydrogen bonds a molecule
must have a hydrogen atom directly bonded
to an oxygen, nitrogen, or fluorine atom. This
is only true for the CH3 CH2 OH molecule.
004 3.0 points
Molecules at the surface of a liquid have a
(lower, higher) energy compared to molecules
in the bulk of the liquid because at the
surface they are experiencing (fewer, more)
intermolecular attractions with neighboring
molecules.
1. higher, more
2. lower, fewer
3. higher, fewer correct
4. lower, more
Explanation:
Molecules at the surface of a liquid have a
higher energy as they are experiencing fewer
attractions to neighboring molecules. Attractive forces lower the energy. The more attractions the lower the energy. Since a molecule at
the surface has fewer molecules surrounding
it, it must experience fewer IMF.
Version 165 – Exam 3 – mccord – (52125)
005 3.0 points
What are the hybrid orbitals used by the
underlined atoms in CH3 CH2 OCH2 CH3 , from
left to right, respectively?
1. sp and sp
2. sp3 and sp3 correct
2
This should be a no-brainer. Most students
want higher scores. If you picked yes, you got
credit for the question and you got the extra
points you asked for (if they were granted
by your instructor). If you answered NO,
you also got what you wanted... no points
awarded.
008 3.0 points
Which molecular geometry is not like the others in the following set of compounds?
3
3. sp and sp
4. sp2 and sp3
1. PO3 3− correct
3
5. sp and sp
2. SO3
Explanation:
H
H3 C
C
H
H
O
C
3. NO3 −
CH3
H
006 2.0 points
Valence band theory deals with the valence
band and conduction band of various chemical
species. Which substance would have the
largest gap between these two bands?
4. CH2 O
5. CO3 2−
Explanation:
All the species shown are trigonal planar except phosphite, PO3 3− . The dot structure for
it shows that there is one lone pair on the
phosphorus, which means that the molecular
geometry is trigonal pyramid.
1. a semi-conductor such as silicon
2. a non-conductor such as glass (SiO2 ) correct
3. a conductor such as iron
Explanation:
007 0.0 points
This question starts out at zero points but
could very well increase after the grading.
Now, if more points are awarded (the curve)
on this assignment, would you like them
added to your score?
1. YES, I would like the points and the
higher score. correct
2. NO, leave my score alone, I prefer the
lower score
Explanation:
009 3.0 points
What is the ground-state electron configuration of O−
2?
1. (σ2s )2 (σ2s ∗)2 (π2p )3 (π2p ∗)1
2. (σ2s )2 (σ2s ∗)2 (σ2p )2 (π2p )3 (π2p ∗)2 (π2p ∗)2
3. (σ2s )2 (σ2s ∗)2 (σ2p )2 (π2p )4 (π2p ∗)2 (π2p ∗)1
correct
4. (σ2s )2 (σ2s ∗)2 (π2p )4 (π2p ∗)1
5. (σ2s )2 (σ2s ∗)2 (σ2p )2 (π2p )4 (π2p ∗)1 (π2p ∗)1
Explanation:
The MO energy diagram will have 13 electrons: (6 from each O and one extra for the
ion charge). The order of filling is shown in
the correct choice above. Remember that for
elements O through Ne, the MO diagram has
Version 165 – Exam 3 – mccord – (52125)
the σ2p orbital lower in energy than the two
degenerate π2p orbitals
010 3.0 points
The viscosity of a liquid depends on which of
the following
I. strength of intermolecular forces.
II. shape of the molecule
III. temperature
1. I, II, and III correct
2. I and II
3. only II
4. only I
5. only III
6. I and III
3
nar electronic geometry. So the initial geometry is for 120◦ bond angles. However, one of
the regions is a lone pair, which will push the
2 N-O bonds closer and therefore result in an
angle that is less than 120◦ . The actual bond
angle for nitrate is about 115◦ .
012 3.0 points
Which of the following is a true statement?
1. Bond strength, bond length and bond
order are not related.
2. Stronger bonds have larger bond lengths
and larger bond orders.
3. Stronger bonds have shorter bond lengths
and larger bond orders. correct
4. Stronger bonds have shorter bond lengths
and smaller bond orders.
Explanation:
The viscosity of a liquid depends on the
strength of intermolecular forces and the particulars of the shape of the molecule. In
addition the viscosity depends on the temperature. As the temperature increase the
molecules have more kinetic energy to overcome the IMF and therefore they flow more
easily.
5. Stronger bonds have larger bond lengths
and smaller bond orders.
011 3.0 points
Which of the following angles is the best
choice to describe the bond angle in nitrite?
013 3.0 points
Given their formulas and melting points identify which of the following is a covalent network solid?
1. slightly less than 109.5◦
2. slightly less than 180◦
3. slightly less than 120◦ correct
4. 109.5◦
5. 180◦
6. 120◦
Explanation:
NO2 − is a bent molecule on a trigonal pla-
Explanation:
Bond order is an indication of bond
strength. The bond order equals the number of bonds. Triple bonds are shorter and
stronger than double bonds which are shorter
and stronger than single bonds.
1. MgO (M.P. = 2852◦ C)
2. KNO3 (M.P. = 334◦ C)
3. W (M.P. = 3422◦ C)
4. BN (M.P. = 2973◦ C) correct
5. HCN (M.P. = -12◦ C)
Explanation:
Covalent network solids have covalent
bonds (between non-metals) and have very
Version 165 – Exam 3 – mccord – (52125)
high melting points. BN and HCN are the
only compounds with only non-metals. BN
is the one with the very high M.P.. MgO is
an ionic solid (metal + non-metal). W is a
metallic solid (only metal). KNO3 is ionic as
it is a metal ion and a polyatomic ion.
014 3.0 points
It is not possible for the dipole moment for a
molecule with a trigonal pyramidal geometry
to be zero.
1. False
2. True correct
Explanation:
The lone pair on the central atom of a
molecule with trigonal pyramidal geometry
will always force the molecule to have a dipole
moment.
015 3.0 points
Which of the following species has the shortest
bond length?
1. NO
2. NO2−
3. NO2+
4. NO−
5. NO+ correct
Explanation:
The bond order for NO+ is 3; the others
have smaller bond orders.
016 3.0 points
Which of the following molecular geometries
is possible around a central atom that is hybridized sp3 d?
1. trigonal planar
2. bent
3. trigonal pyramidal
4
4. linear correct
5. tetrahedral
Explanation:
Linear molecular geometry can have five
regions of high electron density around the
central atom. Tetrahedral, trigonal pyramid,
and bent are all sp3 . Trigonal planar is sp2 .
017 3.0 points
Which compound would be considered the
most polar?
1. CH3 I
2. CH3 Cl correct
3. CH4
4. CI4
5. CCl4
Explanation:
CH4 , CI4 , and CCl4 are all tetrahedral and
therefore non-polar. Cl is more electronegative than I which makes CH3 Cl the most
polar.
018 3.0 points
HI has a higher boiling point than HBr.
Which intermolecular force is the dominant
force for this molecule?
1. dipole-dipole interaction
2. dispersion forces correct
3. H-bonding
Explanation:
Br is more electronegative than I, even
though the boiling point for HI is higher.
This can only be explained by having dispersion forces as the dominant force present. I is
larger and more polarizable than Br, which is
why the dispersion forces are greater for HI.
019
3.0 points
Version 165 – Exam 3 – mccord – (52125)
Which of the following compounds has the
highest vapor pressure?
5
How many carbons are in this structure?
1. ten correct
OH
2. seven
1.
F
correct
2.
NH2
4. nine
5. eleven
3.
4. All three have the same vapor pressure
Explanation:
The alcohol (-OH) and the amine (-NH2 ) will
have H-bonding as the dominant IMF. The
fluoride (-F) is polar, but does not have Hbonding and therefore has the weakest IMFs,
which results in the highest vapor pressure.
020 3.0 points
Which one of the following is a nonpolar
molecule with polar covalent bonds?
Explanation:
The molecular formula is C10 H12 O2
022 (part 2 of 3) 3.0 points
Part 2: What is the hybridization of the
atom shown at the position labeled a ?
1. sp3 d2
2. sp2 correct
3. sp3 d
4. sp3
1. NH3
5. sp
2. H2 Te
Explanation:
The carbon has trigonal planar electronic
geometry, which has sp2 hybridization.
3. SOCl2 (S is the central atom)
4. BeBr2 correct
5. HF
Explanation:
BeBr2 and BeCl2 and BeI2 are exceptions;
these have polar covalent bonds. Since the
shape is linear and the polar bonds are 180◦ ,
the molecule is nonpolar overall.
021 (part 1 of 3) 3.0 points
Part 1: Consider the line structure given
below:
a
O
3. eight
OH
023 (part 3 of 3) 3.0 points
Part 3: Even though there are no lone pairs
shown on this structure, how many lone pairs
are actually there ?
1. one pair
2. three pairs
3. five pairs
4. four pairs correct
5. two pairs
Explanation:
Each oxygen has two lone pairs.
Version 165 – Exam 3 – mccord – (52125)
bb
O
bbH
b
b
b
Ob
024 3.0 points
Consider the solids
ice (solid), CsCl (solid), and Fe (solid) .
Which of the following correctly identifies
the type of solid for ice, CsCl, and Fe, respectively?
1. metallic, ionic, molecular
2. molecular, ionic, metallic correct
3. metallic, ionic, covalent
4. metallic, covalent, ionic
5. molecular, crystalline, ionic
Explanation:
Molecular solids consist of molecules held
together by weak intermolecular forces.
Ionic solids are held together by electrostatic attraction between metal cations and
non-metal anions.
Metallic solids consist only of metals held
together by metallic bonds.
Covalent (or network) solids are like huge
molecules held together by covalent bonds.
025 3.0 points
What is the approximate C-C-C bond angle
in acetone (CH3 COCH3 )?
1. 120◦ correct
2. 180◦
3. 109.5◦
4. 90◦
Explanation:
The molecular geometry of acetone is trigonal planar, which has bond angles of 120◦ .
6
026 3.0 points
Methanol (CH3 OH) has a higher vapor pressure than octanol (C8 H17 OH) because
1. methanol is non-polar and octanol is polar
2. methanol has stronger dispersion forces
than octanol
3. methanol exhibits hydrogen bonding and
octanol does not
4. methanol has weaker dispersion forces
than octanol correct
5. octanol exhibits hydrogen bonding and
methanol does not
Explanation:
Methanol and octanol both are polar and
exhibit hydrogen bonding as a result of the
-OH group in the molecule. However, octanol
is a larger molecule and the long carbon chain
has much larger dispersion forces. As a result
the vapor pressure of octanol is less than 1
Torr at room temperature while methanol is
more than 100 Torr.
027 3.0 points
Which of the following species is not paramagnetic?
1. B2 2− correct
2. OF
3. F2 −
4. N2 3+
5. CN
Explanation:
The answer choices F2 − , OF, CN, and N2 3+
all have an odd number of total electrons and
therefore must be paramagnetic.
028
3.0 points
Version 165 – Exam 3 – mccord – (52125)
As we increase the temperature of a liquid,
its properties change. Which of the following
would NOT be an expected change in the
properties of a typical liquid as we increase its
temperature?
7
1. 4
2. 2
3. 3
1. decrease in density
4. 6 correct
2. increase in vapor pressure
5. 12
3. increase in tendency to evaporate
4. decrease in viscosity
5. increase in surface tension correct
Explanation:
As temperature increases, molecules have
more energy to overcome intermolecular
forces/bonds. Therefore viscosity, surface
tension and density will decrease and vapor
pressure and rate of evaporation will increase.
029 3.0 points
Choose the compound below that does not
exhibit delocalization.
1. O3
Explanation:
The 2pz orbitals of the six carbon atoms
in benzene overlap, forming three pi bonding
and three pi antibonding molecular orbitals
(6 total molecular orbitals: 3 pi-bonding and
3 pi-antibonding). The bonding orbitals form
a delocalized system containing six electrons.
031
3.0 points
Consider the molecule H2 CO. Using valence
bond theory, describe the location of the carbon electrons as it prepares to form bonds
with the other atoms.
1. two electrons in the 2s orbital and two
paired electrons in the 2p orbitals.
2. C6 H6
3. CO3
2−
4. NO3
−
2. four unpaired electrons in sp3 orbitals.
3. three unpaired electrons in sp2 orbitals
and one unpaired electron in a 2p orbital.
correct
5. BrF3 correct
Explanation:
Ozone, benzene, nitrate and carbonate
are all famous examples or delocalization.
Bromine trifluroide does not exhibit delocalization.
030 3.0 points
Benzene (C6 H6 ) is an example of a cyclic,
planar molecule that has a set of extended
delocalized molecular orbitals that occupy the
pi-bonding region above and below the plane
of the six-carbon ring. How many electrons
occupy this molecular orbital set?
4. two unpaired electrons in sp orbitals and
two unpaired electrons in 2p orbitals.
5. two electrons in the 2s orbital and two
unpaired electrons in the 2p orbtials.
6. three unpaired electrons in sp2 orbitals
and one unpaired electron in a 2s orbital.
7. two unpaired electrons in sp2 orbitals and
a pair of electrons in an sp2 orbital.
Explanation:
Version 165 – Exam 3 – mccord – (52125)
O
b
b
b
b
The Lewis structure is
H
C
H
There are 3 RHED around the carbon
atom, implying sp2 hybridization. Initially
the configuration of the isolated carbon atom
is
[He] 2s2 2p2
[He] ↑↓ 2s ↑ ↑
2p
On hybridization we have
[He] ↑ ↑ ↑ sp2 ↑ 2p
The last electron in the p orbital makes a pi
bond to the oxygen atom.
032 3.0 points
What is the molecular geometry of TeCl4 ?
1. tetrahedral
2. square planar
3. trigonal pyramid
4. see-saw correct
5. octahedral
Explanation:
There are 5 electronic regions around the
Te. 4 of them are single bonds to the chlorines
and 1 region is a lone pair. This corresponds
to a see-saw shape.
033 3.0 points
Which of the following compounds has the
highest boiling point?
1. they all have the same boiling point
2. GeCl4
3. SiCl4
4. SnCl4 correct
Explanation:
All three have the same geometry (tetrahedral). The largest molecule is the tin tetra-
8
chloride, which means it will have the highest dispersion forces and therefore the highest
boiling point of the three given.
034 3.0 points
A 500 mL sample of Liquid A at 25◦ C takes
5 minutes to flow through a narrow-necked
funnel. A 500 mL sample of liquid B at 25◦ C
takes 7 minutes to flow through the same sized
funnel. Which of these liquids would you
predict to have the highest surface tension?
1. liquid B correct
2. They have the same surface tension.
3. liquid A
Explanation:
Liquid B has the higher viscosity since it
took longer to flow through the funnel. This
means it probably has stronger IM forces than
liquid A, thus a higher surface tension.
035 3.0 points
A molecule has an angular molecular geometry. The hybridization on the central atom
must be
1. sp3 or sp3 d
2. sp
3. sp or sp2
4. sp3 d
5. sp2 or sp3 or sp3 d
6. sp2
7. sp3
8. sp2 or sp3 correct
Explanation:
Angular molecular geometry is only possible for tetrahedral and trigonal planar electronic geometries which are sp3 or sp2 hybridized, respectively.