6. (7 pts) How much heat in kJ is required to convert 250.0 g of ethanol at -144 oC to the vapor phase at 78 oC?
Ethanol melts at -114 oC and boils at 78 oC. It has a molecular weight of 46.07.
specific heat of solid ethanol
0.97 J/gCC
enthalpy of fusion of ethanol
5.02 kJ/mol
specific heat of liquid ethanol
2.3 J/gCC
enthalpy of vaporization of ethanol
38.56 kJ/mol
1. Which compound of each of the following pairs has the weaker intermolecular forces?
CH4 or C2H6
a)
b)
c)
d)
e)
CH4
C2H6
CH4
C2H6
C2H6
CH3F or H2NCH3
CH3F
H2NCH3
H2NCH3
CH3F
CH3F
H2O or H2S
H2S
H2O
H2O
H2O
H2S
a)
b)
c)
d)
e)
2. Which member of each of the following pairs has the lower vapor pressure at a particular temperature?
NH2NH2 or H2S
a)
b)
c)
d)
e)
NH2NH2
NH2NH2
H2S
H2S
H2S
CF4 or CH2Cl2
CF4
CH2Cl2
CF4
CH2Cl2
CF4
HF or KBr
KBr
KBr
KBr
KBr
HF
3.54 x 105 kJ
2.34 x 105 kJ
1.37 x 104 kJ
3.54 x 103 kJ
354 kJ
Use the graph at the right to sketch the phase diagram for
questions 7 and 8.
triple point = 0 oC, 0.50 atm
normal melting point = -10 oC
critical point = 180 oC, 7.5 atm
normal boiling point = 75 oC
vapor pressure above solid at
-40 oC = 0.10 atm
3. Which of the following statements is not true?
a) Increasing the temperature causes an increase in the vapor pressure of a liquid.
b) Increasing the pressure causes a decrease in the boiling point of a liquid.
c) HF has a higher boiling point than HBr.
d) The stronger the intermolecular forces within a liquid, the higher the heat of vaporization.
e) Ethane, CH3CH3, has a higher vapor pressure than ethanol, CH3CH2OH
7. Which of the following statements is incorrect?
4. Which of the following would result in a higher vapor pressure of the liquid?
a) The substance is a gas at 40 oC and 0.40 atm.
b) The melting point increases with increasing external pressure.
c) The substance can be condensed at 0.65 atm by lowering the temperature.
d) At a pressure of 1.80 atm the boiling point will be greater than 70 oC.
e) Solid, liquid, and gas coexist at 0 oC and 0.50 atm.
a) higher temperature
b) larger volume of liquid
c) greater surface area
d) stronger intermolecular forces
e) more than one of these
8. Which of the following statements is incorrect?
a) The substance will liquefy when the temperature is decreased from 80 oC to -30 oC at 0.35 atm.
b) At -40 oC increasing the pressure from 0.05 atm to 0.80 atm causes deposition to occur.
c) Fusion will occur if the temperature goes from -40 oC to 20 oC at a pressure of 1.40 atm.
d) At 40 oC the substance will evaporate if the pressure is reduced from 1.00 atm to 0.40 atm.
e) Fusion will occur if the pressure drops from 2.00 atm to 0.55 atm at a temperature of -5 oC.
5. Choose the answer that best describes the reason for the shape of a liquid’s meniscus:
a) the viscosity of the liquid
b) the type of the material the container is made of
c) the relative magnitudes of cohesive forces and adhesive forces
d) the amount of hydrogen bonding in the liquid
e) the volume of the liquid
1
2
9. (8 pts) Liquid bromine (Br2, 159.8 g/mol) has a vapor pressure of 392 torr at 41.0 oC and a normal boiling
point of 58.2 oC. Calculate the heat of vaporization of bromine.
a)
b)
c)
d)
e)
15. Consider the solubility of a gas in a liquid solvent with the system at equilibrium. Which of the following
statements is incorrect?
a) Solubility of the gas would increase as the pressure is increased.
b) Solubility of the gas would decrease as the temperature is increased.
c) No change in solubility would occur if the volume of the liquid is increased.
d) If you decrease the pressure and increase the temperature, the result is unpredictable as the two
changes have opposite effects.
e) Increasing the concentration of another gas in solution will have no effect solubility of this gas.
------------------------------------------------------------------------------------------------------------------------Use the KEY LIST at the right to answer
KEY LIST
questions 16-18.
a) Molecular Solid
16. An extremely hard clear solid melting at 3550 oC.
b) Covalent-Network Solid
17. A yellow solid which melts at 144 oC.
Neither solid nor liquid conduct electricity.
c) Ionic Solid
39.2 kJ/mol
35.6 kJ/mol
33.3 kJ/mol
29.1 kJ/mol
25.8 kJ/mol
10. The number of atoms per unit cell in a body centered cubic structure is
a) 1
b) 2
c) 4
d) 6
e) 8
11. A metal oxide of potassium and niobium has a structure described as a primitive cubic cell with potassium
ions at the corners, niobium ions at the center of the cell, and oxygen atoms on the faces. What is the
empirical formula for the compound?
a) KNbO3
b) K2NbO3
c) KNb2O3
d) KNbO6
18. A light grey material that melts at 97.5 oC.
d) Metallic Solid
It conducts electricity and heat readily.
-------------------------------------------------------------------------------------------------------------------------
e) KNb2O4
19. Which member of the following pairs of solutes is expected to be more soluble in hexane, C6H14?
12. Calculate the density in g/cm3 of Iridium (Ir, AW=192.22) which crystallizes in a face-centered cubic cell
with an edge length of 3.83 x 10-8 cm.
a) 2.71
b) 5.68
c) 11.36
d) 14.35
C10H8 or C3H5(OH)3
e) 22.73
a)
b)
c)
d)
e)
13. What is the atomic radius (in cm) of iridium in the previous problem?
a) 5.41 x 10
-8
b) 3.70 x 10
-8
c) 2.71 x 10
-8
d) 1.35 x 10
-8
e) 1.91 x 10
-8
C10H8
C3H5(OH)3
C10H8
C3H5(OH)3
C10H8
, KCl
KCl
, CCl4
, CCl4
, CCl4
,
KCl or CCl4
,
,
,
,
,
C5H12 or C5H11OH
C5H12
C5H12
C5H11OH
C5H11OH
C5H12
20. Which of the following statements about the compounds
shown in the figure to the right is incorrect?
14. Which of the following statements is incorrect?
a)
b)
c)
d)
e)
a) 75.0 g of B can be completely dissolved in 200 g
of water at 80 oC.
b) If the temperature of a saturated solution of A
is raised, solute will crystallize out.
c) If a saturated solution of B is carefully heated
from 70 oC to 90 oC, the solution will be supersaturated.
d) A solution containing 50 g of B in 100 g water at
40 oC is saturated.
e) The order of solubilities at 50 oC is C > B > A.
Aluminum, Al, conducts an electric current.
Liquid SiCl4 does not conduct an electric current.
C3H7OH is a molecular solid.
Solid CuF2 can be hammered out into a thin sheet.
A solid containing hydrogen or halogen atoms cannot be a covalent network solid.
3
4
21. What is the concentration of oxygen in water when the partial pressure of O2 above the solution is 0.28 atm?
Henry’s Law constant for this system is 1.38 x 10-3 mol/LCatm.
a) 7.72 x 10-4 M
b) 3.86 x 10-4 M
c) 1.38 x 10-3 M
d) 2.76 x 10-3 M
a) Colloids consist of particles that are large on the molecular scale, but still small enough to remain
suspended indefinitely.
b) Coagulation is brought about by heating or electrolyte addition.
c) The Tyndall Effect refers to the scattering of visible light by colloids.
d) Hydrophobic colloids remain suspended because they have many non-polar groups on their surface
that interact with water.
e) Stearate ions can be used to stabilize oil in water.
e) 0.431 M
22. (7 pts) What is the molality of a 1.16 M aqueous solution of sugar (C6H12O6, 342.3 g/mol) which has a
density of 1.14 g/mL?
a) 0.442 molal
b) 0.634 molal
c) 0.753 molal
d) 1.56 molal
e) 2.36 molal
Some Useful Information
23. (7 pts) What is the mole fraction of sugar in the solution described in the previous problem?
a) 0.0633
b) 0.0415
c) 0.0329
d) 0.0273
28. Which of the following statements regarding colloids is not true?
Avogadro’s number = 6.022 x 1023
e) 0.0103
gas constant, R = 8.314 J/molCK
24. What is the vapor pressure in torr of water (18.02 g/mol) above a solution prepared by adding 64.0 g of
glycerin (C3H8O3, 92.10 g/mol) to 280.0 g of water at 343 K where the vapor pressure of pure water is 233.7
torr?
a) 7.769
b) 10.16
c) 54.25
d) 189.7
R = 0.08206 LCatm/molCK
Clausius – Clapeyron Equation
e) 223.5
ln P = ! [ )Hv/R] (1/T) + C or
25. (7 pts) Methanol (CH3OH, 32.0 g/mol) and acetone (CH3COCH3, 58.1 g/mol) form ideal solutions. A
solution is prepared by mixing 960 g of methanol and 872 g of acetone. At 25 oC the vapor pressure of pure
methanol is 271 torr and that of pure acetone is 143 torr. Calculate the total vapor pressure in torr of the
solution.
a) 48
b) 133
c) 181
d) 228
ln
P2 − ∆Hvap  1 1 
=
 − 
P1
R  T2 T1 
e) 414
26. Calculate the boiling point of a solution made by dissolving 1.20 moles of a non-volatile solute naphthalene
(C10H8, 128 g/mol) in 1.85 x 103 g of chloroform (CHCl3, 119.38 g/mol). The normal BP of chloroform is
61.2 oC and Kb = 3.63 oC/molal.
a) 57.6 oC
b) 59.1 oC
c) 62.6 oC
d) 63.6 oC
e) 64.9 oC
27. (7 pts) An aqueous solution that contains 0.314 g of penicillin G in 100.0 mL of solution has an osmotic
pressure of 0.230 atm at 25 oC. What is the molecular weight in g/mol of penicillin G?
a) 334
b) 782
c) 1.23 x 103
d) 1.68 x 103
e) 2.13 x 103
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