Download Fall 2012

Chemistry 120A
Exam 1
September 24, 2012
Name __________________
SHOW YOUR WORK. NO WORK, NO CREDIT
INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS
Table of Constants
N A  6.022 x 1023
particles
mole
c  2.998 x 108
m
s
h  6.626 x 1034
J s
photon
0°C = 273.15 K
Up to 75% of the credit for a problem will be given for correctly setting it up, including labels on all numbers and proper number of
significant figures
On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and
that the work of others in this class has, to the best of my knowledge, been honest as well.
Signed __________________________________________________________________________
If you feel you can’t sign this, contact the instructor (e-mail or in person)
(2 pts each) Multiple choice - circle the correct answer
1.
2.
Which of the following is a violation the lab safety agreement?
a) wearing a jacket or sweater in lab.
b) arriving late for lab.
c) wearing shorts on a warm day.
d) spilling a reagent solution while dispensing it.
What is the symbol (metric system prefix) that represents the factor 10 -6?
a) n
3.
4.
5.
6.
b) μ
c) p
d) m
If hitting the bull’s eye is the desired result, the figure on the right represents
a) poor accuracy and poor precision.
b) poor accuracy and good precision.
c) good accuracy and poor precision.
d) good accuracy and good precision.
The following diagram represents the reaction of A2 (unshaded spheres) with B (shaded spheres). What
is the balanced chemical equation for this reaction?
A) A2 + B ! A2B
B) 4A2 + 6B ! 2A4B
C) 2A2 + B ! A4B
D) 4A + B ! A4B
Which of the following is a chemical property of iron?
a.
Iron melts at 1535 °C.
b.
Iron rusts on exposure to water and oxygen.
c.
Iron can be bent into shapes.
d.
Iron conducts electricity.
Which of the following is a metalloid?
a.
silicon (14Si)
b.
chlorine (17Cl)
c.
uranium (92U)
1
d.
tungsten (74W)
7.
What is the proper answer and number of significant figures for the following calculation: (28.914 - 19.3) x 8.152?
a.
8.
78.37
78
c.
78.4
d.
78.373328
Which element can be classified as a lanthanide?
a.
9.
b.
81
Tl
b.
90
Th
c.
65
Tb
d.
43
Tc
Which of the following represent a pair of isotopes?
37
17
Cl
80
35
I.
a.
Br
II.
35
17
Cl
III.
II and IV
35
18
Ar
IV.
b.
I and III
c.
IIII and IV
d.
II and III
10. Which of the following is an ionic compound?
a.
CO
b.
c.
PCl3
NH4NO2
d.
Cl2
11. In the reaction Cu(s) + H2SO4(aq) ! CuSO4(aq) + H2(g), which substances are NOT dissolved in water?
a.
Cu
b.
H2SO4 and CuSO4
c.
H2 and Cu
d.
H2 and H2SO4
12. An organic compound has an empirical formula of C2H3O and an approximate molecular weight of 130 g/mole. What is its molecular
formula?
a.
C10H15O5
b.
C 6 H9 O3
c.
C 4 H6 O2
d.
C 2 H3 O
13. Which of the following elements has chemical properties similar to arsenic (33As)?
a) gallium (31Ga)
b) silicon (14Si)
c) phosphorus (15P)
d) selenium (34Se)
14. If WO4-2 is called tungstate, then the formula for pertungstate would be
a)
WO2-2
b) WO4-3
c)
WO5-2
d) WO3-2
15. (2 pts) Write the formula of the compound that results when VO2+1 combines with Fe(CN)6-3.
16. (2 pts) What is the temperature shown on the Celcius thermometer on the right?
17. (3 pts each) Name the following compounds.
a.
ClO2
________________________________
b.
Mg3N2
________________________________
18. (3 pts each) Write the formula for each of the following compounds.
a.
cobalt nitrite
________________________________
b.
arsenic (III) carbonate
________________________________
2
19. An element has three naturally occurring isotopes with the following masses and abundances (in parenthesis): 27.977 amu (92.22%);
28.974 amu (4.69%); 29.974 amu (3.10%).
a.
(7 pts) What is the atomic mass of that element?
b.
(2 pts) What is the identity element? ____________
20. (9 pts) How many sulfate ions are there in 2.500 mL of 5.0 x 10 -15 M Cr2(SO4)3 solution?
21. (9 pts) The following diagram represents the reaction of A2 (small, unshaded spheres) with B (large,
shaded spheres). How many moles of product can be produced from the reaction of 1.0 mole of A2 and
1.0 moles of B? Explain your reasoning.
22. (10 pts) A hydrate of magnesium sulfate, MgSO4 · nH2O loses 37.4% of its mass upon heating. If heating
removes all the water and leaves only MgSO4, what is the value of n in the formula?
23. (9 pts) UV radiation with a wavelength of 350 nm is blocked by the ozone layer. What is the frequency of this radiation in gigahertz
(GHz). Giga = 109.
24. Carbon disulfide is a smelly, but useful solvent. It is produced by reacting graphite (C) with sulfur dioxide as shown.
C
+
SO2 !
CS2 +
CO
a.
(4 pts) Balance the reaction.
b.
(6 pts) In an experiment 25.00 moles of carbon was reacted with excess sulfur dioxide, and 4.00 moles of carbon disulfide was
actually collected. What is the percent yield of carbon disulfide in this reaction?
Chemistry 120
Exam 2
October 26, 2012
Name __________________
SHOW YOUR WORK. NO WORK, NO CREDIT
INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS
The last page is the periodic table. You may remove it if you like.
Table of Constants
N A  6.022 x 1023
particles
mole
c  2.998 x 108
m
s
h  6.626 x 1034
J s
photon
0°C = 273.15 K
Up to 75% of the credit for a problem will be given for correctly setting it up, including labels on all numbers and proper number of
significant figures
On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and
that the work of others in this class has, to the best of my knowledge, been honest as well.
Signed __________________________________________________________________________
If you feel you can’t sign this, contact the instructor (e-mail or in person)
(2 pts each) Multiple choice - circle the correct answer
3
25. If l = 2, which of the following values is NOT a possible value for mR?
a.
0
b.
-1
c.
+2
d.
-3
26. Which description of a π (pi) bond is FALSE?
a.
cannot form from hybrid orbitals
b.
always appears with a σ (sigma) bond
c.
end to end overlap of orbitals
d.
orbital overlap is between parallel orbitals
27. Which of the following compounds will dissolve in water in large amounts at 20 °C?
Ca(NO3)2
I
a.
II & III
b.
III & IV
c.
MgCO3
II
III & IV
PbI2
III
d.
K2PO4
IV
I & IV
28. Neon’s electron configuration is 1s2 2s2 2p6. What is the set of quantum numbers for the 6th electron in the 2p orbital?
a.
n = 2, R = 1, mR = +1, ms = -1/2
b.
n = 2, R = 2, mR = -1, ms = -1/2
c.
n = 2, R = 1, mR = 0, ms = -1/2
d.
n = 1, R = 1, mR = 1, ms = -1/2
29. Which of the following has the largest ionic radius?
a.
F -1
b.
K+
c.
Ar
d.
P -3
30. Which element has the largest first ionization energy?
a.
Ca
b.
Ge
c.
As
d.
Br
31. Which bond is shortest?
a.
C/O bond
b.
C=C bond
c.
C-O bond
d. they are the same length
32. Which of the following represents a non-polar covalent bond?
a.
C-N
b.
S-O
c.
C-C
d.
Li-F
33. Which element is the most electronegative?
a.
carbon
b.
phosphorus
c.
sulfur
d.
oxygen
d.
neutral (neither acid or base)
34. In water the hydrogen sulfite ion, HSO3-1, is
a.
an acid
b.
a base
c.
amphiprotic
35. The number of π bonds in the molecule on the right is
3
b.
4
c.
9
d.
H
H
C
C
C
H
O
H
N
a.
H
12
C
H
36. How many valence electrons will there be in the correctly drawn Lewis structure for CH3NH3+1?
a.
14
b.
15
c.
16
d.
17
37. You used ethanol (ethyl alcohol) in the average atomic mass lab. The primary safety hazard for this reagent is
a.
acute poison when ingested
C
b.
turns the skin yellow
4
c.
seriously corrosive to skin and eyes
d.
flammable, keep away from flames
38. Which one of these equations describes a precipitation reaction?
a.
2Al + 3H2SO4 ! Al2(SO4)3 + 3H2
b.
2NH4OH + Pb(NO3)2 ! 2NH4NO3 + Pb(OH)2
c.
ZnBr2 + Na2SO4 ! ZnSO4 + 2NaBr
d.
CO3 -2 + HSO4 -1 ! HCO3 -1 + SO4 -2
39. (3 pts) What is the formal charge on N in the Lewis structure on the right? Show your work.
O
C
N
40. (3 pts each) Name the following compounds:
Cr(OH)3
_____________________________
NH4C2H3O2
_____________________________
41. (3 pts each) Write formulas for the following compounds:
lead phosphite
_______________________
mercury(I) fluoride
_____________________________
42. (6 pts) What is the electron configuration for 74W? You may start with a noble gas core.
43. (5 pts) The electron configuration for 46Pd is [Kr] 5s2 4d8. Is Pd+3 expected to be a stable charge? Explain your reasoning.
44. (5 pts) Is the S+4 ion paramagnetic or diamagnetic? Explain your reasoning.
45. (6 pts each) Draw the Lewis structures, including any resonance structures, for: C2F2Cl2 and SiO3 -2
46. (1 pt each blank) Fill in the blanks for each Lewis structure.
F
H
F
Se
S
F
H
F
Shape __________________________
Shape __________________________
Polar (yes/no) __________________________
Polar (yes/no) __________________________
Hybrid ________________________________
Hybrid ________________________________
H-Se-H bond angle ____________________________
F-S-F bond angle(s) ____________________________
47. (5 pts) Nitrogen and phosphorus are in the same group, so you would expect them to exhibit similar chemical properties. NCl3, PCl3,
and PCl5 are all stable compounds that are easily synthesized in the lab. However, NCl5 has never been synthesized or observed. Why
would phosphorus form two compounds with chlorine, but nitrogen forms only NCl3, and not NCl5?
48. The precipitation reaction below occurs when aqueous solutions of the reactants are mixed.
NiSO4
+ Na3PO4
! Ni3(PO4)2
+
a.
(4 pts) Designate physical states (s, l, g, aq) for the reactants and products.
b.
(6 pts) Write and balance the net ionic reaction.
Na2SO4
49. (6 pts) The longest wavelength of light (lowest energy) that can eject an electron from the surface of cesium is 318 nm. What is the
ionization energy of cesium in kJ/mole?
5
Chemistry 120
Exam 3
November 14, 2012
Name __________________
SHOW YOUR WORK. NO WORK, NO CREDIT
INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS
Table of Constants
m
Js
c  2.998 x 108
h  6.626 x 1034
0°C = 273.15 K
s
photon
L  atm
L  torr
J
R = 0.08206
= 62.36
= 8.314
K  mole
K  mole
K  mole
particles
mole
J
Cp (H 2 O) = 4.184
g  deg
N A  6.022 x 1023
Up to 75% of the credit for a problem will be given for correctly setting it up, including labels on all numbers and proper number of
significant figures
On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and
that the work of others in this class has, to the best of my knowledge, been honest as well.
Signed __________________________________________________________________________
If you feel you can’t sign this, contact the instructor (e-mail or in person)
(2 pts each) Multiple choice - circle the correct answer
50. Which substance is oxidized in the reaction NaNO3 + Pb ! NaNO2 + PbO
a.
PbO
b.
NaNO2
c.
NaNO3
d.
Pb
51. Which of the following has the highest melting point?
Cl
a.
H
F
b.
Cl
C
H
c.
H
Li
+
O
-2
Li
d.
+
Cl
H
P
H
H
H
52. What is the major type of force that must be overcome to allow the evaporation of liquid CH2Cl2?
H
Cl
a.
London (dispersion) forces
b.
hydrogen bonding
c.
dipole-dipole
d.
ion-ion
C
Cl
H
53. The vapor pressure for water is lower than expected for a polar substance with its molar mass because of which forces?
a.
London (dispersion) forces
b.
hydrogen bonding
c.
dipole-dipole
d.
ion-ion
54. A product development lab has identified three reactions as “safe” for use in commercial products. Which reaction should you use
to produce a hot pack?
a.
one with ΔH = + 145 kJ/mole
b.
one with ΔH= 0.00 kJ/mole
c.
one with ΔH = - 145 kJ/mole
d. none of them
55. (2 pts) Which of the following is a strong base in water?
a.
NaCl
b.
NH3
c.
H2SO4
d.
6
Ba(OH)2
56. Starting with a saturated solution of sodium chloride in water at room temperature, adding solid sodium chloride will
a.
decrease the concentration of NaCl in the solution.
b.
decrease the anion concentration and increase the cation concentration of the solution.
c.
increase the concentration of NaCl in the solution.
d.
have no effect on the concentration of NaCl in the solution.
57. A bicycle pump plunger is drawn half way and the inlet sealed at 25°C (orig). With the piston allowed to move freely, the temperature
is increased to 50°C. Which diagram most closely represents the position of the piston at 50°C?
orig
a.
b.
c.
d.
58. Which one of these equations describes a redox reaction?
a.
Cu(NO3)2 + 2 NaOH ! Cu(OH)2 + 2 NaNO3
b.
CuO + H2SO4 ! CuSO4 + H2O
c.
Cu + 4 HNO3 ! Cu(NO3)2 + 2 NO2 + 2 H2O
d.
5 H2O + CuSO4 ! CuSO4@5H2O
c.
a redox reaction.
59. The reaction CuO + H2SO4 ! CuSO4 + H2O is
a.
a precipitation reaction.
b.
an acid-base reaction.
d.
none of these choices.
60. Which box represents the system with the highest entropy?
a.
box (a)
b.
box (b)
c.
box (c)
d. box (d)
61. (2 pts) Which noble gas is least like an ideal gas at high pressures?
a.
He
b.
Rn
c.
Ar
d. all deviate from ideality equally
62. While working in the lab you accidentally spill about 10 mL of 1 M H2SO4 on the benchtop. You make a quick check of yourself and
find no evidence of splashes. What should you do next?
a.
It’s not particularly hazardous, so get some paper towels and clean up the mess.
b.
It’s too hazardous to leave, but does not pose an immediate threat. Calmly notify the instructor or lab assistant.
c.
It poses a serious threat to the class, quickly notify the instructor or assistant and warn classmates to stay away.
d.
It’s not much and it is not bothering anyone, so just ignore it and continue with the lab.
63. (3 pts each) Name the following compounds.
H3PO3
______________________________
Sn(SO5)2
__________________________________
64. (3 pts each) Write formulas for the following compounds.
iodic acid
______________________
nickel dichromate
7
___________________
65. (10 pts) Using the standard enthalpies of formation given in the table, determine the ΔH for the reaction:
2 CO2 (g) + 3 H2O (l) ! C2H5OH (l) + 3 O2 (g).
66. (10 pts) Balance the following redox reaction which takes
place in acid solution.
H3AsO3 +
Sn+2 !
Sn+4 +
As
CO(g)
-110.5 kJ/mol
CO2(g)
-393.5 kJ/mol
H2O(l)
-285.8 kJ/mol
H2O(g)
-241.8 kJ/mol
H2O2(l)
-187.8 kJ/mol
CH3OH(g)
-200.7 kJ/mol
C2H5OH(l)
-277.7 kJ/mol
C2H5OH(g)
-235.1 kJ/mol
67. (11 pts) When 35.00 mL of 0.100 M HBr is added to 0. 275
g of strontium hydroxide in a calorimeter, 195.3 J of energy
are released. What is the ΔH for this reaction? The balanced reaction is: Sr(OH)2 + 2 HBr ! SrBr2 + 2 H2O
68. (11 pts) One type of weather balloon has a volume limit of 2.00 x 105 L. A meteorologists wants to check the atmospheric conditions
at 10,000 m where the temperature is expected to be -10.3 °C and the pressure will be around 420 torr. What is the maximum volume
of helium that the meteorologist can put in the balloon at 723.1 torr and 27.3 °C (conditions on the earth's surface) that will allow
cruising at 10,000 m without exceeding the volume limit of the balloon?
69. The following molecular reaction takes place in aqueous solution
HCl
+ Rb2SO3
! H2SO3
a.
(4 pts) Assign physical states (s, l, g, aq) to each reactant and product.
b.
(6 pts) Write and balance the corresponding net ionic equation.
+ RbCl
70. (10 pts) How many molecules of N2 are in a 500.0 mL container at 50.0 mm Hg and 135°C?
Chemistry 120
Exam 4
December 7, 2012
Name __________________
SHOW YOUR WORK. NO WORK, NO CREDIT
INCLUDE LABELS AND PROPER NUMBER OF SIG FIGS
Up to 75% of the credit for a problem will be given for correctly setting it up, including labels on all numbers.
Equations and Constants Given on the ACS Exam
R = 8.314 J mol 1 K 1 = 0.0821 Latmmol1 K 1
F = 96500 Cmol1 = 96500 J V 1 mol1
N A = 6.022 x 1023 mol1
c = 2.998 x 108 ms 1
h = 6.626 x 1034 J s
Ea
0°C = 273.15 K
12
M 
rateA
Arrhenius Equation: k = Ae
Graham's Law of Effusion:
= B
rateB
 MA 
RT
0.05916
Nernst Equation: E = E° ln(Q) Nernst Equation at 25°C: E = E° ln(Q)
nF
n
1
1
Integrated Rate Laws zero: [A] = [A]0 - kt first: ln[A] = ln[A]0 - kt
second:
= kt +
[A]
[A]0
RT
On my honor, I pledge that I have upheld the Honor Code, and that the work I have done on this assignment has been honest, and
that the work of others in this class has, to the best of my knowledge, been honest as well.
Signed __________________________________________________________________________
If you feel you can’t sign this, contact the instructor (e-mail or in person)
8
(2 pts each) Multiple choice - circle the correct answer
1.
The primary safety concern when running reactions that generate hydrogen is that hydrogen
a.
is flammable.
b.
d.
2.
reacting acids with NaOH
c.
precipitating AgCl using NaCl
reactions with HNO3 that produce NO2 (g)
H3O+ and CH2NH2-1
b.
H3O+ and CH3NH-1
OH-1 and CH3NH3+
c.
OH-1 and CH4NH2+
d.
a.
acetic acid (Ka = 1.8 x 10-5)
b.
formic acid (Ka = 1.8 x 10-4)
c.
dihydrogen phosphate (Ka = 2.9 x 10-7)
d.
benzoic acid (Ka = 6.3 x 10-5)
What is the hydronium ion concentration of an acid rain sample that has a pH of 3.35?
10-(14.00-3.35) M
b.
- log (14.00 - 3.35) M
c.
- log (3.35) M
10-3.35 M
d.
Consider the equilibrium system ZnSO3 (s) º Zn+2 (aq) + SO3-2 (aq). If HBr is added,
a.
7.
diluting a solution of CuSO4
Which acid, in combination with its conjugate base, would be the best choice to make a buffer of pH = 3.70?
a.
6.
b.
Methylamine, CH3NH2, acts as a weak base in water. What are the products of the reaction CH3NH2 + H2O !?
a.
5.
is a suspected carcinogen.
has a penetrating odor and is corrosive.
d.
4.
c.
Which of the following situations should be carried out in a hood?
a.
3.
is an acute poison
the amount of solid will be unchanged. b.
the solid will dissolve.
c.
more solid will form.
d. explode.
The equilibrium constant is equal to 5.00 at 1300 K for the reaction 2 SO2 (g) + O2 (g) W 2 SO3 (g). If initial concentrations are
[SO2] = 3.0 M, [O2] = 2.0 M, and [SO3] = 2.0 M, the system is
a) not at equilibrium and will shift to the right (form products) to achieve an equilibrium state.
b) not at equilibrium and will remain in an unequilibrated state.
c) not at equilibrium and will shift to the left (form reactants) to achieve an equilibrium state.
d) at equilibrium.
8.
Which of the following covalent compounds is most soluble in hexachloroethane (Lewis structure on the right)?
Cl
Cl
Cl
C
C
Cl
Cl
O
H
a.
acetaldehyde
C
H
C
H
b.
carbon disulfide
S
C
S
H
Cl
c.
trichloroacetic acid
Cl
C
Cl
9.
F
O
d.
C
O
sulfur tetrafluoride
F
S
H
F
Which of the following will form neutral solutions when dissolved in water (all of them are soluble)?
9
F
Cl
a.
II & III
b.
I & II
NaNO3
KHSO4
NH3
ZnCl2
Sr(OH)2
I
II
III
IV
V
c.
I & IV
d.
only I
10. The pictures on the right represent aqueous solutions of three acids HA (A = X, Y, or Z), with
water molecules omitted for clarity. Unshaded spheres represent hydrogen atoms or ions and
gray spheres represent A atoms or ions. Which of the three is the strongest acid?
a.
HX
b.
HY
c.
HZ
d.
All three are the same strength.
11. For the reaction 4 NO2(g) + O2(g) ! 2 N2O5(g), if the rate of disappearance of O2 is -0.0450 mol L-1 s-1, what is the rate of formation
N2O5(g)?
a.
0.0225 mol L-1 s-1
b.
0.0450 mol L-1 s-1
c.
0.0900 mol L-1 s-1
d.
0.180 mol L-1 s-1
12. The rate of the chemical reaction involving two substances, A and B, is measured. It is found that if the initial concentration of A is
tripled, keeping the B concentration the same, the rate triples. If the concentrations of both A and B are doubled, the rate is eight times
that measured in the first experiment. The rate law for this reaction is
a.
Rate = k[A][B]2.
b.
Rate = 2k[A][B].
c.
Rate = k[A]2[B].
d.
Rate = k[A][B]/2.
13. From the stoichiometry of the reaction 2 I-1 (aq) + H2O2(aq) + 2 H3O+(aq) ! I2(s) + 4 H2O(l), the rate law
a.
is predicted to be first-order in all reactants.
b.
is predicted to be first-order in I2(s).
c.
is predicted to be fifth-order overall.
d.
cannot be predicted.
14. (3 pts each) Name the following compounds.
Co(C2H3O2)2
______________________________
HNO2
__________________________________
15. (3 pts each) Write formulas for the following compounds.
copper (I) sulfite
______________________
lead dioxide
________________________
16. (12 pts) Write the equilibrium constant expression for the net ionic reaction below.
2 MnO4-1 (aq) + CH3OH (aq) + 2 H3O+ (aq) º CO2 (g) + 2 MnO2 (s) + 5 H2O (l)
Keq =
17. (12 pts) According to the label, bleach is 6% NaClO. When mixed with water, would you expect this product to be acidic, basic, or
neutral? Explain your reasoning.
18. (14 pts) What is the pH of a solution that contains 0.50 M HNO2 and 0.25 M KNO2? Ka for HNO2 is 7.18 x 10-4.
19. (12 pts) What is the pH of an aqueous 2.0 x 10-5 M BaO solution?
20. (12 pts) Radioactive decay is a first order process (reaction). If a sample of 233Pa takes 62.7 days to decrease to 20.0% of its original
mass, what is its half-life?
10