Practice Exam 4 – Chapters 8, 10, 11
Multiple Choice (3 points each)
_____1. Which compound has the largest (most negative) lattice energy?
A) CaO
B) MgO
C) CaS
D) MgS
_____2. What is the formal charge on chlorine if the compound has this Lewis structure?
A) 0
F) -3
B) +3 G) -5
C) +5 H) -7
D) +7 I) -4
E) + 4
_____3. How do the magnitudes of the H-N-H bond angles vary in these species?
A) NH2- < NH3 < NH4+
B) NH2- < NH4+ < NH3
C) NH3 < NH2- < NH4+
D) NH3 < NH4+ < NH2_____4.Which molecule has the greatest bond energy?
A) CO
B) O2
C) NO
D) F2
_____5. The bonds in ozone, O3, are best represented as
A) distinct single and double bonds
B) a single and a double bond that switch positions rapidly
C) something between a single and a double bond
D) two double bonds
_____6. Select the most polar bond.
A) C-O
B) Si-F
C) Cl-F
D) C-F
E) F-F
_____7. When these substances are arranged in order of increasing boiling point (lowest
boiling point first), what is the correct order?
A) NH3 < PH3 < AsH3
B) AsH3 < PH3 < NH3
C) PH3 < AsH3 < NH3
D) AsH3 < NH3 < PH3
_____8. Analysis of an unknown substance showed that it has a high boiling point and is
brittle. It insulates as a solid but conducts electricity when melted. This could be
A) HCl
B) Al
C) KBr
D) SiF4
_____9. The pressure on a sample of water at its triple point is reduced while the
temperature is held constant. Which phase change(s) are favored?
I. fusion
II. sublimation
III. vaporization
A) I only
B) III only
C) I and II only
D) II and III only
_____10. If a solute dissolves in an endothermic process,
A) H bonds must exist between the solvent and the solute.
B) strong ion-dipole forces must exist in the solution.
C) the entropy of the solution must be greater than that of its pure components.
D) the process gives off heat.
11. (6 pts) Consider the related species, CO and CO2.
A) Draw Lewis structures for each.
B) Compare the C-O bond lengths expected for each species and explain your reasoning.
12. (4 pts) Draw molecular distribution vs. kinetic energy for a liquid at two temperatures
and use it to explain why vapor pressure increases with temperature.
13. (10 pts) For each of the following substances, circle the one intermolecular force
which would predominate in the solid or the liquid.
Substance
C2H6
Ionic
DipoleH
London
Dipole
Bonding
Dispersion
Al2O3
Ionic
DipoleDipole
H
Bonding
London
Dispersion
CH3OH
Ionic
DipoleDipole
H
Bonding
London
Dispersion
F2
Ionic
DipoleDipole
H
Bonding
London
Dispersion
CH3F
Ionic
DipoleH
London
Dipole
Bonding
Dispersion
14. (8 pts) Draw a phase diagram for sulfur dioxide, SO2 given the following data:
normal melting point = -72.7 oC
normal boiling point = -10 oC
triple point = -75 oC at 10 torr
A) Plot Pressure on the vertical axis and temperature on the horizontal axis. Label the
normal melting point, the normal boiling point, the triple point, and the predominate
phase (s. l. or g) in each region of the diagram.
B) What change in state occurs when SO2 at -25 oC and 5 torr has its pressure increased
to 760 torr at -25 oC?
__________________________
15. (16 pts) Draw Lewis Structures for the following species. Use formal charge to draw
the best structure. Show resonance forms if needed.
A) ONCl (this is the order the atoms are bonded)
B) IF3
C) XeOF2 (all atoms bonded to Xe)
D) NO2- ion
E) Complete the following table:
Species
VSEPR Shape (Geometry)
Molecular Shape
(Geometry)
ONCl
IF3
XeO2F2
NO216. A) Show Lewis structures for
(8 pts)
i) CH2F2
B) Make a perspective (3 dimensional)
drawing of
i) CH2F2
ii) SF4
ii) SF4
17. (4 pts) State whether each of the following is polar or nonpolar.
A) CH2F2
________________
B) SF4
________________
C) IF3
________________
D) SO3
________________
18. (6 pts) How would you prepare 1.000 kg of a 5.555 m ethanol, C2H5OH, in water?
19. (6 pts) If 1.10 g of an unknown compound reduces the freezing point of 75.22 g of
benzene from 5.53 to 4.92 oC, what is the molar mass of the compound?
20. (6 pts) The normal boiling point of acetone is 56.2 oC and its Hvap is 32.0 kJ/mol.
What is the vapor pressure of acetone at 25.0 oC?
21. (6 pts) In an experiment to determine the molar mass of aspirin, it is found that 0.250
L aqueous solution of aspirin has an osmotic pressure of 0.271 atm. Calculate the molar
mass of aspirin.
Useful Information
Solvent
Benzene
Water
Kf (oC/m)
5.12
1.86
Constants
R = 8.3145 J/mol.K = 0.08206 L.atm /
mol.K
k = 1.38 x 10-23 J/molecule.K
1 J = 1 kg.m2/s2
h = 6.63 x 10-34 J.s
N = 6.022 x 1023
c = 2.998x108 m/s
RH = 2.18 x 10-18 J
Kp = Kc(RT)n
n = mol product gas-mol
reactant gas
pH + pOH = 14.00
pX = -log X
KaKb = Kw = 1.0 x 10-14
Equations
M = n/V
XA = nA/(nA + nB)
m = moles solute
1 kg solvent
PA = XAPAo
PA = XBPAo
TFP = kFP . m
TBP = kBP . m
 nRT/V
  1 1 
  
ln P2 – ln P1 = R  T2 T1 
PV = nRT
pH  PK a  log
[base]
[acid ]
Ek = 1/2 mu2 = 3/2 kT per molecule
Ek = ½ Mu2 = 3/2 RT per mole
u2

u2
M1
M2
= Rate of Effusion1
Rate of Effusion2
h

c 
h/mv
p = mv
p.x>h/2 
En = - RH/n2
q = smT
 = n RT = MRT
V

