Chem 1721/1821
Exam 1
9:00
OR
Dr. Susan Bates
11:00
February 13, 2014
ID #: 2014172 _____
Name ______________________________________
NA = 6.022 x 1023 mol—1
C = kP
R = 8.314 J/K•mol = 0.08206 L•atm•K—1•mol—1
Psoln = χsolv•P°solv
Π=MRT
ln
IA
II A
III B
IV B
VB
VI B
q = msΔT
ΔTb = Kb•m
ΔTf = Kf•m
∆H!"# 1
!! 1
= − !!
R
T! T!
VIII
VII B
IB
II B
III A
IV A
VA
VI A
1
VII A inert
gases
2
H
He
1.008
3
4
5
6
7
8
9
4.003
10
Li
Be
B
C
N
O
F
Ne
6.941 9.012
11
12
10.81 12.01 14.01 16.00 19.00 20.17
13
14
15
16
17
18
Na Mg
22.98 24.31
19
20
K
Ca
Al
21
22
23
24
Sc
Ti
V
Cr
25
26
27
Mn Fe Co
28
Ni
29
30
Si
P
S
Cl
Ar
26.98 28.09 30.97 32.06 35.45 39.95
31
32
33
34
35
36
Cu Zn Ga Ge As
Se
Br
Kr
39.10 40.08 44.96 47.90 50.94 52.00 54.94 55.85 58.93 58.71 63.55 65.37 69.72 72.59 74.92 78.96 79.90 83.80
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb
Sr
Y
Zr
Nb Mo Tc
Ru Rh Pd Ag Cd
In
Sn Sb
Te
I
Xe
85.46 87.62 88.91 91.22 92.91 95.94 98.91 101.0 102.9 106.4 107.8 112.4 114.8 118.6 121.8 127.6 126.9 131.3
55
56
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
*
Cs
Ba
La
Hf
Ta
W
Re Os
Ir
Pt
Au Hg
Tl
Pb
Bi
Po
132.9 137.3 138.9 178.4 180.9 183.8 186.2 190.2 192.2 195.0 196.9 200.5 204.3 207.2 208.9 (210)
87
88
89
104
105
106
107
108
109
110
111
112
113
114
*
Fr
Ra
Ac Rf
(223) 226.0 (227) (261)
Db Sg
Bh Hs
(262)
(263)
(262)
60
61
58
59
Ce
Pr
Mt
(265) (266)
62
63
Nd Pm Sm Eu
140.1 140.9 144.2 (147) 150.4 151.9
90
91
92
93
94
95
Th
Pa
U
(269)
(272)
64
65
Gd
Tb
(242)
(243)
(277)
66
?
67
Dy Ho
(289)
68
69
70
Er Tm Yb
71
Lu
157.3 158.9 162.5 164.9 167.3 168.9 173.0 174.9
96
97
98
99
100
101
102
103
Np Pu Am Cm Bk
232.0 (231) 238.0 (237)
At
(247)
(247)
Cf
Es Fm Md No
(251) (254)
(253)
(256)
(254)
Rn
(210) (222)
Lr
(257)
Chem 1721/1821: Exam 1
Name _________________________________________
Part I (40 points): Short Answer.
1.
2.
Consider the following compounds, and then answer a - d below. Blanks may have only one or more than one correct
answer; indicate all compounds that match the given criteria.
SF4
CF4
XeF4
PF5
a.
Which of these have at least 1 nonbonding pair of electrons on the central atom?
_______________________
b.
Which of these use sp3 hybrid orbitals for σ bond formation?
_______________________
c.
Which of these have trigonal bipyramidal electron domain geometry?
_______________________
d.
Which of these have only London dispersion forces between molecules?
_______________________
Circle the one best answer for the following:
a. Which phase(s) of a substance is generally stable at conditons of low pressure and high temperature?
solid
b.
gas
gas and solid
solid and liquid
What is the name of the P and T coordinate on a phase diagram at which the solid, liquid, and gas phases exist in a
state of dynamic equilibrium?
critical point
3.
liquid
vapor pressure curve
normal sublimation point
boiling point
triple point
Calculate the energy (in kJ) released when 150.0 g X (g) at 250ºC is cooled and converted to X (l) at its boiling point.
Some data for X: molar mass = 87.85 g/mol; bp = 212ºC; ∆Hvap = 61.4 kJ/mol; s (g) = 0.706 J/gºC.
_____________________ kJ
4.
5.
Consider 2 nonpolar compounds Y (molar mass = 151.4 g/mol) and Z (molar mass = 62.7 g/mol).
a.
Which compound should have a higher boiling point?
____________
b.
Which compound should have a higher vapor pressure at 25ºC?
____________
Consider the compounds shown below:
O
H2
C
H3C
H2
C
C
H2
C
C
H2
A
OH
H3C
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
H2
C
C
H2
B
Which of these {A, B, or C} should be the most hydrophilic?
6.
H2
C
C
H2
H2
C
C
H2
H2
C
O
C
H2
C
OH
H2
C
HO
C
H2
OH
C
____________
100.0 g iron (III) chloride (molar mass = 162.2 g/mol) is dissolved in water to produce 400.0 mL of solution. Determine
the molar concentration of chloride ions in this solution.
[Cl–] = _____________________ M
7.
a.
0.150 mol naphthalene (C10H8) is dissolved in 2.65 mol toluene (C7H8). If the vapor pressure of the resulting solution
is 20.8 torr, determine the vapor pressure (in torr) of toluene. Naphthalene is a nonvolatile, nonelectrolyte solute.
_____________________ torr
b.
If more naphthalene is added to the solution described in a above, will the vapor pressure of the solution
increase, decrease, or remain constant?
8.
a.
__________________________
Put solutions A, B, and C (identified below) in order of increasing freezing point:
0.30 m NaCl (aq)
sol'n A
0.30 m Na2SO4 (aq)
sol'n B
0.40 m NiSO4 (aq)
sol'n C
____________________ < ____________________ < ____________________
lowest fp
highest fp
b.
Put compounds A, B, and C (identified below) in order of increasing vapor pressure at 25ºC:
CH3CH2CHOH
cmpd A
C3H8
cmpd B
HOCH2CH2CH2OH
cmpd C
____________________ < ____________________ < ____________________
lowest Pvap
highest Pvap
c.
Put solids A, B, and C (identified below) in order of increasing melting point:
KBr
solid A
Zn
solid B
C10H8
solid C
____________________ < ____________________ < ____________________
lowest mp
highest mp
9.
The concentration of dissolved O2 gas in water at 25ºC is 5.9 x 10–4 mol/L under PO2 = 0.450 atm.
a.
If the temperature is increased to 50ºC, will the solubility of O2 (g) increase, decrease, or remain constant?
___________________________
b.
Determine the concentration of O2 gas (in mol/L) dissolved in water at 25ºC if the PO2 is increased to 2.50 atm. For
O2 in water, k = 0.00131 mol/L•atm
__________________________
Part II (45 points): Multiple Choice. Use the Scan-Tron sheet provided to indicate the ONE best answer for each of the
following.
1.
Calculate ppb concentration of mercury in a lake if a 450.0 g sample of lake water is found to contain 8.975 µg Hg.
a. 19.55 ppb
d. 0.01944 ppb
b. 19.94 ppb
e. 4.039 ppb
c. 0.004039 ppb
2.
3.
Consider the phase diagram shown to the right. At approximately
what temperature does this substance melt at a pressure of 9.0 atm?
a. 70ºC
c. 90ºC
e. 200ºC
b. 250ºC
d. substance does not melt at 9.0 atm
Consider again the phase diagram shown. Which of the following is
true for this substance?
a. The substance has both a normal melting point & normal boiling point.
b. The liquid phase is more dense than the solid phase.
c. Above 250ºC a distinct liquid phase can not exist.
d. At a pressure of 3.0 atm, the liquid phase exists over the temperature range of 50ºC to 250ºC.
e. All of these are true.
4.
Ethylene glycol (HOCH2CH2OH) is a slightly viscous liquid that boils at 198ºC. Pentane (C5H12) has approximately the
same molar mass but is a nonviscous liquid with bp = 36ºC. Which one of the following is the best explanation of this?
a. London dispersion forces in ethylene glycol are stronger than London dispersion forces in pentane.
b. Pentane is nonpolar and therefore has only dispersion forces; ethylene glycol is polar and can hydrogen bond.
c. Both compounds are polar, but ethylene glycol has more surface area and therefore the dispersion forces are stronger.
d. Pentane molecules can form hydrogen bonds to one another which causes the bp to be lower.
e. There is no explanation for this - it is the opposite of what is expected.
5.
Which of the following properties indicates the existence of strong intermolecular forces?
a. low bp
6.
c. high viscosity
d. high Pvap
e. all of these
Which of the following changes for a substance X will require absorption of the greatest amount of energy?
a. X (s)  X (l)
7.
b. small ∆Hfus
b. X (g)  X (l)
c. X (s)  X (g)
d. X (l)  X (g)
e. X (l)  X (s)
If 0.611 mol of a nonelectrolyte solute is dissolved in 425.0 g of benzene, what will be the freezing point of the solution?
For benzene, Kf = 5.065 ºC/m; fp = 5.455ºC.
a. 7.29ºC
d. 4.02ºC
b. 1.84ºC
e. –1.84ºC
c. 1.44ºC
8.
Which one of the following statements is true?
a. Molecular solids are held together by a long-range network of covalent bonds.
b. Ionic compounds are good conductors in the solid state.
c. Metallic bonds are generally stronger than covalent or ionic bonds.
d. Covalent-network solids have only weak intermolecular forces between particles and therefore low melting points.
e. In general, molecular solids are insulators.
9.
10.
At an atmospheric P = 1.25 atm benzene boils at 88.0ºC. Which one of the following must be true?
a. at 88.0ºC Pvap > 1.25 atm
c. at atomspheric P = 785 torr, bp > 88.0ºC
b. at 88.0ºC, Pvap = 760 torr
d. the normal bp of benzene is < 88.0ºC
Which of the following should be more soluble in pentane than in water?
i. NH3
a. only i
11.
e. all of these are true
ii. CCl4
iii. C6H14
b. ii, iii, and iv
c. only iv
iv. NaCl
d. only iii
e. ii and iii
Consider the unit cell shown to the right. Which one of the following is not true?
a. the particle in the middle is not shared with other unit cells
d. the body diagonal = 4r
b. each particle in this lattice touches 4 other particles
e. for this unit cell, volume = 3
c. the lattice represented by this unit cell has an AB AB repeating layer pattern
12.
Vanadium (density = 6.11 g/cm3) has a body-centered cubic structure. Calculate the volume (in cm3) of a unit cell of V.
a. 2.77 x 10–23 cm3
d. 6.43 x 10–3 cm3
b. 5.54 x 10–23 cm3
e. 1.03 x 10–21 cm3
c. 1.38 x 10–23 cm3
13.
The vapor pressure of a liquid increases with increasing T. Which of the following statements best explains why?
a. The average kinetic energy of molecules is greater, so more molecules can enter the gas phase.
b. The number of gas molecules above the liquid remains constant, but these molecules have greater kinetic energy.
c. The molecules in the liquid move faster and exert a greater pressure.
d. All the molecules have greater average kinetic energies.
e. The intermolecular forces between the molecules decreases at higher temperature.
14.
In your Structures of Molecules and Solids lab, you built models of five straight-chain alkanes: methane (CH4), ethane
(C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12). Which of the following is the best explanation of why the
melting and boiling points of these hydrocarbons increase as chain length increases?
a. As the number of carbon atoms increases, the polarity of the molecules decreases.
b. As the molar mass of the hydrocarbon increases, the strength of London dispersion forces decreases.
c. As the number of atoms in the molecule increases, the strength of hydrogen-bonding forces increase.
d. As chain length and molar mass increase, the polarizeability of the molecules increases.
e. All of these are true.
15.
Data analysis for the Enthalpy of Vaporization experiment yielded a line with the equation:
1
ln !!"# = −4610 ! ∗ + 17.8
!
Using this data, what is the experimental value for ΔHvap?
a. 17.8 kJ/mol
b. –38.3 kJ/mol
c. –21.4 kJ/mol
d. 38.3 kJ/mol
e. 148 kJ/mol
Part III (15 points): Problems. Work each of the following problems. Show all work; work with units in all steps;
report all answers with appropriate units and significant figures. No partial credit will be given if I cannot follow your
work.
1.
Calculate the vapor pressure (in torr) of chloroform at 25ºC. The normal boiling point of chloroform is 61.7ºC, and
∆Hvap = 31.4 kJ/mol.
Pvap = ______________________ torr
2.
20.0 mg of insulin is dissolved in water resulting in a 5.00 mL solution. The osmotic pressure of the solution is measured
to be 12.5 torr at 300 K. Determine the molar mass of insulin.
molar mass = _________________________ g/mol
3.
A solution of hydrogen peroxide in water is 35.0% H2O2 by mass, and has a density of 1.13 g/mL. Determine the molal
concentration and molar concentration of this solution.
molal concentration = ____________________________
molar concentration = ____________________________