6B CHEM PRACTICE EXAM 2-2 (Prof. Crowell)
Winter 2012
Feb. 19, 2012
*** FILL IN YOUR STUDENT ID NUMBER, NAME, and TEST FORM = A ***
Bubble in the correct response on scantron (26 questions, worth 4 pts each)
1. Consider the following four molecules 1-4, all
with molecular formula C6H14:
Which has the lowest vapor pressure?
a) 1
b) 2
c) 3
d) 4
e) All have the same vapor pressure because they
have the same molecular formula.
2. Based on the phase diagram shown, which of the following
statements are correct?
1. Sublimation occurs at a point along the straight line
connecting point A to point H.
2. Hvap can be measured at point F.
3. Points C and E represent points where the solid and
gas phases are in equilibrium.
4. At point E the vapor pressure of the solid and liquid phases
are in equilibrium.
5. The temperature at point B is called the critical temperature.
a) 2, 4
b) 1, 3, 5
c) 3, 4, 5
d) 1, 2, 3
e) 3, 4
3. At 2000C, Kp = 0.01 for the reaction N2 (g) + O2 (g) 2 NO (g). Predict how the concentrations will
change to reach equilibrium at 2000C if 0.4 moles of N2, 0.1 moles of O2, and 0.08 moles of NO are placed in
a 1.0 L container.
a) The concentrations of NO, N2 and O2 will remain unchanged.
b) The concentration of NO will increase; the concentrations of N2 and O2 will decrease.
c) The concentration of NO will decrease; the concentrations of N2 and O2 will remain unchanged.
d) The concentration of NO will decrease; the concentrations of N2 and O2 will increase.
e) The concentrations of NO, N2 and O2 will all increase.
4. A 0.450 molal aqueous solution of cesium bromite (CsBrO2) freezes at 1.51C. Given this information,
what is the value for the vant Hoff factor i which describes the relationship between the moles of particles in
solution compared to the moles of solute dissolved? Kf = 1.86 C kg/mole for H2O.
a) 1.8
b) 1.5
c) 2.1
d) 0.55
e) 2.7
5. For the reaction:
2 SO3 (g) + 2 Cl2 (g) 2 SO2Cl2 (g) + O2 (g),
Kp = 4.74 x 10-3 at 325 K.
Calculate the value of Kc at 325 K for the related reaction: 2 SO2Cl2 (g) + O2 (g) 2 SO3 (g) + 2 Cl2 (g)
a) 7.81
b) 5.56 x 103
Chem 6B Practice Exam 2-2
c) 2.08 x 102
1-A
d) 1.80 x 10-4
e) 0.128
Prof. Crowell
6. The vapor pressure of pure benzene (C6H6) at 25C is 94.4 torr while the vapor pressure of pure chloroform
(CHCl3) at 25C is 172 torr. An ideal solution is formed when 50 g of chloroform is added to 50 g of benzene.
Calculate the vapor pressure of chloroform over this chloroform-benzene solution at 25C.
a) 86 torr
b) 68 torr
c) 148 torr
d) 125 torr
e) 172 torr
7. At 1000C, Keq = 0.403 for the following reaction: FeO (s) + CO (g) Fe (s) + CO2 (g).
If CO gas at 5.5 atm is injected into a container at 1000C that contains excess FeO (s), what is the
partial pressure of CO2 (g) at equilibrium?
a) 1.58 atm
b) 5.5 atm
c) 3.16 atm
d) 2.30 atm
e) 1.15 atm
8. Silver chloride, AgCl, crystallizes with the rock salt (NaCl) ionic crystal structure. The length of the unit cell edge
(i.e. the lattice parameter a) is 5.55 angstroms (1 angstrom = 10-8 cm). What is the density of AgCl, in g/cm3?
a) 6.1 x 106
b) 11.14
c) 4.19
d) 5.57
e) 1.38
9. Hydrogen peroxide (H2O2) is a powerful oxidizing agent used in concentrated solution in rocket
fuels and in dilute solution as a hair bleach. An aqueous solution of H2O2 is 30.0 % by mass and has a
density of 1.11 g/mL. Calculate its molarity (in mol/L).
a). 0.013
b). 9.79
c). 8.8
d). 12.6
e). 300
10. The addition of 125 mg of caffeine to 100 g of cyclohexane lowered the freezing point by 0.13 K.
Calculate the molar mass of caffeine. The Kf for cyclohexane is 20.1 Kkgmol1.
a). 47.8 gmol1
b). 19.3 gmol1
c). 481 gmol1
d). 193 gmol1
e). 96.5 gmol1
11. Which of the following solutes dissolved in 1.0 kg of water would be expected to boil at the highest
temperature?
a) 0.020 moles of potassium sulfate, K2SO4.
b) 0.035 moles of sucrose, C12H22O11.
c) 0.040 moles of glucose, C6H12O6.
d) 0.025 moles of sodium nitrate, NaNO3.
e) 0.015 moles of magnesium chloride, MgCl2
12. Consider the following reaction:
3 N2H4(g) + 4 ClF3(g) 12 HF(g) + 3 N2(g) + 2 Cl2(g)
A mixture, initially consisting of 0.880 M N2H4(g) and 0.880 M ClF3(g), reacts at a certain
temperature. At equilibrium, the concentration of N2(g) is 0.525 M. Calculate the concentration of
Cl2(g) at equilibrium.
a) 0.700 M
b) 0.175 M
c) M
d) 0.525 0.350 M
e) 0.705 M
13. The coordination numbers (number of nearest neighbors) of atoms in face-centered cubic, body-centered
cubic, and the diamond structures, respectively, are
a) 12, 8, & 12
b) 8, 6, & 4
Chem 6B Practice Exam 2-2
c) 12, 8, & 4
2-A
d) 12, 8, & 6
e) 8, 6, & 12
Prof. Crowell
14. The molecules in a liquid mixture of water and 2-propanone are attracted to each other by a combination of:
a) ionic bonding
b) covalent bonding
c) London dispersion forces only
d) London dispersion forces, dipole-dipole interactions, & hydrogen bonding
e) London dispersion forces & dipole-dipole interactions only
15. Consider the following reaction
NO (g) + O2 (g) NO2 (g)
If H = 56.52 kJ and S = 72.60 JK at 298K, calculate the equilibrium constant KP for the
reaction at 298K.
a) 1.31 106
b) 7.63 107
c) 660
d) 1.22 1014
e) 8.08 109
16. Which of the following solutes is likely to be most soluble in water?
a) Br2
b) CS2
d) sulfur hexabromide, SBr6
c) ethanol, CH3CH2OH
e) carbon tetrachloride, CCl4
17. The equilibrium constant for the reaction CO (g) + H2O (g) CO2 (g) + H2 (g) is K = 9.00 at
700K. If 1.0 mole of each reactant and each product (i.e. 1.0 mole each of CO, H2O, CO2, and H2)
are combined in a 5.0 liter vessel at 700 K, what is the concentration of CO (g) at equilibrium?
a) 0.061 M
b) 0.50 M
c) 0.10 M
d) 1.39 M
e) 0.050 M
18. Which of the following would be expected to be characteristic of n-type silicon?
1.
2.
3.
4.
5.
Electrons are the mobile charge carriers.
The electrical conductivity increases with increasing temperature.
The dopant could be Boron.
The dopant could be Phosphorus.
Holes are the mobile charge carriers.
a) 1, 2, 3
b) 2, 4, 5
c) 2, 5
d) 3, 5
e) 1, 2, 4
19. Consider the following reaction:
2 SO3 (g) + 2 Cl2 (g) 2 SO2Cl2 (g) + O2 (g), H = 422 kcal/mol.
Predict the effect of:
(1). removing Cl2 (g) from the equilibrium mixture,
(2). raising the temperature of the equilibrium mixture,
(3). decreasing the volume of the container filled with the equilibrium mixture.
a) (1) shifts left, (2) shifts left, (3) shifts right.
b) (1) shifts left, (2) shifts right, (3) shifts left.
c) (1) shifts left, (2) shifts right, (3) unchanged.
d) (1) shifts left, (2) shifts right, (3) shifts right.
e) (1) shifts right, (2) shifts left, (3) shifts right.
20. The vapor pressure of methanol at 25C is 123 Torr and its enthalpy of vaporization is 35.3
kJmol. Estimate the normal boiling point of methanol. Assume the enthalpy of vaporization is
independent of temperature.
a). 450 K
b). 373 K
Chem 6B Practice Exam 2-2
c). 342 K
d). 315 K
3-A
e). Not enough information given
Prof. Crowell
21. Given:
SO2 (g) O2 (g) + S (s)
Kc = 2.5 1053
Kc = 4.0 1013
SO3 (g) O2 (g) + SO2 (g)
2 S (s) + 3 O2 (g) 2 SO3 (g)
Calculate Kc for the reaction
a) 1.0 1065
b) 1.0 10130
c) 1.6 1080
d) 1.6 10103
e) 1.6 1040
22. 6.04 g of a compound of unknown molecular weight is dissolved in 100 g of chloroform (CCl4). The
boiling point is found to be 78.75C as a result. The normal boiling point of chloroform is 76.50C. What is the
molecular weight of the unknown substance? Please Note: Kb = 5.03C kg/mole for chloroform. (Assume the
vant Hoff factor to be equal to one for this unknown compound).
a) 240 g/mole
b) 170 g/mole
c) 200 g/mole
d) 38.6 g/mole
e) 135 g/mole
23. For each of the following groups of substances, pick the one that has the given property for each of the
items (i), (ii), and (iii), respectively.
(i) Highest boiling point: CH4, CF4, H2O.
(ii) Greatest heat of vaporization: HCl, HBr, HI.
(iii) Lowest melting point: NaCl, N2, CHCl3.
a) H2O, HI, NaCl
b) H2O, HCl, NaCl
d) CH4, HCl, N2
c) CF4, HBr, CHCl3
e) H2O, HI, N2
24. The combustion of propane in the presence of oxygen is described by the following balanced
C3H8(g)+ 5O2(g) 3CO2(g) + 4H2O(g),
equation:
Ho = 300 kJ/mol.
Which of the changes listed below would cause the equilibrium for this reaction to shift farthest to the
left?
a) increase the temperature
c) increase the volume
b) selectively remove CO2
d) both a & c
e) both b & c
25. The osmotic pressure, in atm, of a 0.075 M solution of NaCl in water at 0C is approximately:
a) 1.84 atm
b) 1.68 atm
Chem 6B Practice Exam 2-2
c) 3.67 atm
4-A
d) 6.72 atm
e) 3.36 atm
Prof. Crowell