6B CHEM PRACTICE EXAM 2-1 (Prof. Crowell)
Winter 2012
Feb 18, 2012
*** FILL IN YOUR STUDENT ID NUMBER, NAME, and TEST FORM = B ***
Bubble in the correct response on scantron (25 questions, worth 4 pts each)
1. Based on the phase diagram shown, which of the following
statements are correct?
1. Sublimation occurs anywhere along the curve connecting
point B to point D.
2. Hfus can be measured at point F.
3. Point E represents a condition where the solid and
liquid vapor pressures are the same.
4. At point F the number of independent variables (degrees of
freedom) when the liquid and gas are in equilibrium is two.
5. The temperature at point D is called the critical temperature.
a) 2, 4
b) 3, 5
c) 1, 3, 5
d) 3, 4, 5
e) 1, 2, 5
2. 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) Lowest vapor pressure: CH4, CH3OH, C2H4.
(ii) Greatest volatility (vapor pressure): CF4, CBr4, CCl4.
(iii) Lowest boiling point: CH3(CH2)3CH3, C(CH3)4, (CH3)2CHCH2CH3.
a) CH4, CCl4, CH3(CH2)3CH3
c) CH4, CF4, C(CH3)4
b) CH3OH, CBr4, (CH3)2CHCH2CH3
d) CH3OH, CF4, C(CH3)4
e) C2H4, CCl4, CH3(CH2)3CH3
3. Identify the substance from each of the following pairs with the highest boiling point:
I. H2O or NH3
a) H2O, H2, CH3(CH2)3CH3
II. He or H2
III. CH3(CH2)3CH3, or C(CH3)4
b) NH3, H2, CH3(CH2)3CH3
d) NH3, He, CH3(CH2)3CH3
c) NH3, He, C(CH3)4
e) H2O, He, C(CH3)4
4. Which of the following indicates very weak intermolecular forces of attraction in a liquid?
a) a very high heat of vaporization
b) a very high vapor pressure
c) a very high boiling point
d) a very large viscosity
e) a very large surface tension
5. Which of the following statements is true about p-type silicon?
a)
b)
c)
d)
e)
Electrons are the mobile charge carriers.
It does not conduct electricity as well as pure Si.
It can be produced by doping Si with P or As.
It conducts electricity better than a metal, even at low temperatures.
Answers a, b, c, & d are all false.
Chem 6B Practice Exam 2-1
1-B
Prof. Crowell
6. Potassium sulfide crystallizes in an ionic structure in which the S2- ions are in a face-centered cubic lattice
and the K+ ions are in tetrahedral holes. The number of K+ ions in this unit cell is:
a) 1
b) 2
c) 4
d) 6
e) 8
7. The metal titanium, Ti, has a body centered cubic unit cell. The density of titanium is 4.50 g/cm3. Calculate
the edge length (i.e. the lattice parameter a) for the unit cell, in angstroms (1 = 10-8 cm).
a) 2.60
b) 4.13
c) 3.28
d) 5.32
e) 6.71
8. The molecules in a sample of solid CHF3 are attracted to each other by a combination of:
a)
b)
c)
d)
e)
London dispersion forces & Hydrogen-bonding
Hydrogen-bonding & covalent bonding
Hydrogen-bonding & dipole-dipole interactions
London dispersion forces & dipole-dipole interactions
Hydrogen bonding, London dispersion forces & dipole-dipole interactions
9. Which of the following solutes dissolved in 1.0 kg of water would be expected to boil at the highest
temperature? Assume all of the salts fully dissociate to ions.
a) 0.040 moles of rubidium chloride, RbCl.
b) 0.035 moles of magnesium nitrate, Mg(NO3)2.
c) 0.025 moles of sodium selenide, Na2Se.
d) 0.025 moles of ferric (iron III) chloride, FeCl3.
e) 0.045 moles of calcium sulfite, CaSO3.
10. Calculate the solubility (in moles/liter) of N2 in water at a partial pressure of N2 of 435 torr at 20C. The
Henrys law constant for N2 in water at 20C is 7.0 x 10-4 mol / liter - atm.
c) 4.0 x 10-4
a) 3.0 x 105
b) 1.0 x 10-2
d) 2.1 x 10-4
e) 3.0 x 10-1
11. A 0.750 molal aqueous solution of lithium fluoride (LiF) freezes at 1.95C. 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) 2.3
b) 1.9
c) 1.4
d) 0.8
e) 2.8
12. The molecular mass of hemoglobin (with i = 1) is 6.86 x 104 g/mol. What mass of hemoglobin must be
present in 150.0 mL of solution to exert an osmotic pressure of 132.2 torr at 25C?
a) 5.56 kg
b) 87.2 g
c) 23.0 37.6 g
d) g
e) 73.2 g
13. Calculate the total vapor pressure at 25C of a mixture of benzene and toluene in which the mole fraction
of benzene is 0.650. The vapor pressure at 25C of benzene is 94.6 Torr and that of toluene is 29.1 Torr.
a) 84.4 Torr
b) 124 Torr
Chem 6B Practice Exam 2-1
c) 51.3 Torr
2-B
d) 71.7 Torr
e) 61.5 Torr
Prof. Crowell
14. Seawater is approximately 0.55 M NaCl. What is the minimum pressure that must be applied at 15C to purify
water using reverse osmosis?
a) 18 torr
b) 26 atm
c) 13 atm
d) 1.35 atm
e) 0.68 atm
15. The vapor pressure of water at 70C is 365 torr. What is the vapor pressure (in torr) of an ideal solution made by
dissolving 0.90 moles of glucose (C6H12O6) in 144 g of water?
a) 37
b) 244
c) 328
d) 3.2
e) 363
16. What is the boiling point for a solution containing 40.2 g of anthracene (a nonvolatile, nondissociating hydrocarbon molecule of formula C14H10) in 285. g of liquid benzene? (Note: the
normal boiling point of benzene, C6H6, is 80.10C, and Kb = 2.53 C/m for benzene).
a) 82.10C
b) 78.10C
c) 83.42C
d) 80.46C
e) 85.00C
17. The osmotic pressure, in atm, of a 0.03 M solution of Mg(NO3)2 in water at 10C is approximately:
a) 2.09 atm
b) 0.025 atm
c) 7.74 atm
d) 0.074 atm
e) 0.70 atm
18. Given the equilibrium constants for reactions 1 and 2 below at 450K, calculate the equilibrium
constant for reaction 3 at this same temperature:
K1 = 3.3 x 104.
Rxn 1:
N2O5 (g) 2 NO2 (g) + O2 (g),
Rxn 2:
2 NO (g) + O2 (g) 2 NO2 (g),
Rxn 3:
4 NO (g) + 3 O2 (g) 2 N2O5 (g),
b) 26.6
c) 0.5
a) 5.16
K2 = 6.4 x 103.
K3 = ??
d) 0.51
e) 0.038
19. For the reaction N2O4(g) 2 NO2(g), Kc = 0.21 M at 100C. Shortly after mixing N2O4 & NO2,
the concentrations are measured and found to be [N2O4] = 0.12 M and [NO2] = 0.55 M. Calculate the
reaction quotient Q and determine in which direction the reaction will proceed to reach equilibrium.
a) Q = 0.21 M, at equilibrium
b) Q = 4.6 M, left
d) Q = 2.5 M, right
c) Q = 2.5 M, left
e) Q = 4.6 M, right
20. Consider the following reaction (assume an ideal gas mixture): 2 NOBr (g) 2 NO (g) + Br2 (g)
A 1.0 L vessel was initially filled with pure NOBr, at a pressure of 5.0 bar, at 300K. After equilibrium was
established, the partial pressure of NOBr was 3.5 bar. What is Kp for this reaction?
a) 0.14
b) 0.75
c) 0.48
d) 0.27
e) 0.32
Chem 6B Practice Exam 2-1
3-B
Prof. Crowell
21. 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 ClF3(g) at equilibrium.
a) 0.180 M
b) 0.175 M
22. Consider the following reaction:
c) 0.525 M
d) 0.350 M
e) 0.705 M
4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (g);
A mixture, initially consisting of 7.2 torr of NH3 (g) and 6.4 torr of O2 (g), reacts at a certain temperature. At equilibrium, the partial pressure of H2O (g) is 2.4 torr. Calculate the partial pressure of O2 (g) at
equilibrium.
a) 4.4 torr
b) 5.6 torr
c) 3.4 torr
d) 0.4 torr
e) 1.6 torr
23. Consider the following reaction at equilibrium: 4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (g); with
H = 44 kJ. The amount of NO (g) produced by this reaction can be maximized by carrying out the reaction
at:
a) high temperature and low pressure (i.e. large volume)
b) high temperature and high pressure (i.e. reduced volume)
c) low temperature and high pressure (i.e. reduced volume)
d) low temperature and low pressure (i.e. large volume)
e) temperature and pressure (volume) have no effect on this reaction
24. For the reaction 2 SO2 (g) + O2 (g) 2 SO3 (g), 3.00 torr of SO2 (g) and 2.20 torr of O2 (g)
are placed in a 1.00 L container. At equilibrium, the total pressure is found to be 4.4 torr. What is the
value of Kp under these conditions?
a) 983
b) 437
c) 0.933
d) 612
e) 700
25. At 700C, Kp = 0.55 for the reaction 4 NO (g) + 6 H2O (g) 4 NH3 (g) + 5 O2 (g). What is the
value of Kc at 700C?
a) 6.8 x 103
b) 44.5
Chem 6B Practice Exam 2-1
c) 4.4 x 103
4-B
d) 32.0
e) 31.6
Prof. Crowell