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Name:
_____________________________________________________________
(Print)
Surname
Given Names
Student Number:____________________________________
The Irving K. Barber School of Arts and Sciences
CHEMISTRY 121 FINAL EXAM
Instructors: Dr. Ed Neeland and Dr. Karen Perry
DATE: Thursday, Dec. 6, 2007
Time: 9:00am – 12:00pm
Duration: 3 Hours
This exam contains pages numbered 1 through 14, and a data sheet. You may detach the data sheet.
Instructions:
Answer the questions in the space provided. You may use the backs of pages for calculations if necessary.
You must clearly show all your work to receive full credit for the calculation problems.
Make sensible use of significant figures and include units with the final answer whenever appropriate.
Total marks = 99
DO NOT WRITE IN THESE BOXES
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Σ
99
2
1. Fill in the blanks in the following table:
Symbol
[3 marks]
protons
2. Sulfur exists in nature as three isotopes:
isotope?
32
neutrons
electrons
net charge
16
18
-3
S ,
33
S , and
34
S. Which of the three is the predominant
[1 mark]
3. The density of mercury metal is 13.60 g/mL. What is the volume (in mL) of one mole of mercury?
[2 marks]
4. Compute the answer to the following expression using the correct number of significant figures: [1 mark]
5.
Name the following compounds:
[3 marks]
Give the formula for:
iron(III) hydroxide
Ag2CO3
ammonium sulphate
P4S10
phosphoric acid
CuI2
[3 marks]
3
6. The depletion of ozone (O3) in the stratosphere has been a matter of great concern among scientists in
recent years. Consider the reaction shown below.
[5 marks]
-1
Molar masses (g mol ): O3 48.00, O2 32.00, NO 30.01, NO2 46.01
a. If 0.740 g of O3 reacts with 0.670 g of NO, how many grams of NO2 will be produced? State which reactant
is limiting and show how you arrived at this conclusion.
O3 + NO → O2 + NO2
b. Calculate the mass of the excess reagent.
4
7. A compound X contains 63.3 % manganese and 36.7 % oxygen by mass. When X is heated, oxygen gas
is evolved and a new compound Y containing 72.0 % Mn and 28.0 % O is formed. Determine the empirical
formulas of X and Y.
[4 marks]
+
8. Calculate the final molarity of K (aq) in a solution made by mixing 200.0 mL of a 0.115 M solution of
K3PO4(aq) with 300.0 mL of a 0.225 M solution of K2CO3(aq). Note that both salts are completely soluble in
water and assume that the volumes are additive.
[3 marks]
5
9. A chemist weighed out 1.654 g of a mixture containing unknown amounts of iron (Fe) and lead (Pb) and
placed the sample in a 0.500 L flask containing O2(g) at 24.0°C and 846 torr. After heating, the reaction to
form Fe2O3(s) and PbO2(s) was completed, the vessel was cooled to 24°C and the pressure of O2(g)
remaining was 452 torr. Calculate the mass percentage of lead in the mixture.
[6 marks]
-1
Molar masses (g mol ): PbO2 239.20; Fe2O3 159.69; Pb 207.20; Fe 55.85
6
10. What is wrong, if anything, with the following sets of quantum numbers. For the correct sets name the
orbitals.
[3 marks]
n
l
ml
2
2
1
1
/2
3
2
0
1
/2
5
1
2
- /2
Allowed
(yes or no – if no give a reason)
ms
Orbital
(if allowed)
1
11. A hydrogen electron makes a transition from n=6 to n=2.
[4 marks]
a. Calculate the wavelength of the photon emitted.
b. Could this photon initiate a photoelectric effect in gold (threshold frequency = 1.17 x 10
your answer.
15
Hz)? Explain
12. The following are electron configurations for the outer shell of a phosphorus atom. Indicate whether the
configurations represent the ground state or a state that is inconsistent with Hund’s Rule. Justify your
answers. Circle what is wrong.
[2 marks]
Configuraton
a.
b.
3s
3px
3py
3pz
answer
7
13. Give the electronic configurations for:
[2 marks]
Se
Cd
2+
14. Answer the following:
[4 marks]
a. Write the following ions in the order of increasing radius:
b. Circle the element with the lowest ionization energy.
Ca
K
2+
Mg
S
2-
Cl
O
-
K
He
+
P
Cl
3-
Li
c. Circle the maximum number of electrons in an atom which may have quantum numbers n = 4 and l = 2.
6
4
10
8
2
d. Circle the element with the greatest electronegativity:
12
14
Ca
S
l
15. Circle the element(s) that behave chemically similarly to calcium.
magnesium
sodium
sulphur chlorine
iron
1
Mg
[1 mark]
berillium
16. Draw the orbital for an electron with quantum numbers (5,1,-1,+ /2)
[1 mark]
17. Is the O-H bond in a molecule of water:
[1 mark]
a. ionic
b. polar covalent
c. nonpolar covalent
d. hydrogen bond
O
8
18. For the molecule presented below:
[4 marks]
a. Indicate the hybridization on the arrowed atoms in the above molecule.
b. How many σ bonds are present? _____________
c. How many π bonds are present? _____________
19. Draw the VSEPR shape of the following molecules, specifying both the electronic and the molecular
geometry.
[6 marks]
a. PF3
b. BrF5
9
20. State whether the following molecule has a dipole moment. To obtain full marks you must draw the
VSEPR shape showing the lone pairs on the central atom and the electronegativity (dipole moment) vectors.
(all bonds in the molecule are single)
[3 marks]
I3
-
21. Draw all Lewis structures that obey the octet rule for the molecule HCNS. The arrangement of the atoms
is as written.
[3 marks]
10
22. Using the molecular orbital energy levels below and bond orders, determine which of the two molecules
BeC and BN:
[5 marks]
σ1s < σ1s* < σ2s < σ2s* < σ2px < π2py = π2pz < π2py* = π2pz* < σ2px*
a. has the shortest bond ?
b. has the weakest bond ?
c. is/are diamagnetic ?
23. A sample of ammonia (NH3) gas is completely decomposed to nitrogen and hydrogen gases over heated
iron wool. If the total pressure is 115.5 kPa, calculate the partial pressures of N2 and H2 in kPa. [4 marks]
11
24. A quantity of 0.225 g of a metal, M (molar mass = 27.0 g/mol) was reacted with excess HCl, forming a
chloride and liberating 0.303 L of molecular hydrogen (measured at 17.0ºC and 0.975 atm). Deduce from
these data the molecular formula of the metal chloride and write the balanced reaction showing this process.
[4 marks]
25. In each of the following groups of substances, circle the one that has the given property.
a. Largest vapour pressure at 25°C:
SiH4
PH3
NH3
[2 marks]
PCl3
b. Highest boiling point:
26. Which of the following gases cannot be liquefied at 25ºC?
a. N2, critical temperature = 126 K
b. CO2, critical temperature = 405 K
c. CH4, critical temperature = 191 K
d. O2, critical temperature = 155 K
e. propane, critical temperature = 370 K
[1 mark]
12
27. A small cylinder of helium gas used for filling balloons has a volume of 2.30 L and a pressure of 136 atm
at 25ºC. How many balloons can you fill if each one has a volume of 1.5 L and a pressure of 1.25 atm at
25ºC.
[3 marks]
28. Rationalize the following differences in physical properties by describing the intermolecular forces in each
compound. Compare the first two substances with each other and compare the last three substances with
each other. Why is the bp of diethylether the same as n-pentane?
[4 marks]
Substance
n-pentane
n-hexane
Molecular formula
CH3CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
diethylether
ethanol
1-propanol
CH3CH2OCH2 CH3
CH3CH2OH
CH3CH2CH2OH
bp (°C)
36
69
36
78
97
13
3
30. Manganese, density 7.43 g/cm crystallizes with a body centred cubic unit cell. Estimate the percentage
-1
of free space in the unit cell of manganese metal. Atomic mass of manganese is 54.938 g.mol . [5 marks]
14
31a. Sketch the phase diagram for ammonia given the following data. You must clearly label the axes, the
following 3 points and the 3 phases on the phase diagram.
[6 marks]
triple point, 195 K and 0.060 atm
normal melting point, 196 K
normal boiling point, 240 K
b. A chemist wants to perform a synthesis in a vessel at a pressure of 0.2 atm using liquid ammonia as a
solvent. What temperature range would be suitable?
c. In part (b), the chemist wanted to boil off the solvent without raising the temperature above 200 K once the
synthesis was complete. Could she do this and if so, how?
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Equations
PV = nRT
Constants
RH = 2.18 x 10
-18
J
-1
Planck’s constant = 6.626 x 10
-1
-1
R = 8.314 J mol K = 0.08206 L atm mol K
-34
.
8
Js
. -1
speed of light = 3.00 x 10 m s
-1
NA = 6.022 x 10
23
atoms mol
-1
Conversions
.
2
1 J = 1 kg m s
-2
1 atm = 101.325 kPa = 760 torr = 760 mmHg = 14.70 psi
K = °C + 273
Periodic Table of the Elements
1
2
H
He
1.008
4.003
3
4
5
6
7
8
9
10
Li
Be
B
C
N
O
F
Ne
6.941
9.012
10.81
12.01
14.01
16.00
19.00
20.18
11
12
13
14
15
16
17
18
Na
Mg
Al
Si
P
S
Cl
Ar
22.99
24.31
26.98
28.09
30.97
32.06
35.45
39.95
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
39.10
40.08
44.96
47.87
50.94
52.00
54.94
55.85
58.93
58.69
63.55
65.41
69.72
72.59
74.92
78.96
79.90
83.80
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
85.47
87.62
88.91
91.22
92.91
95.94
(98)
101.1
102.9
106.4
107.9
112.4
114.8
118.7
121.8
127.6
126.9
131.3
55
56
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.9
137.3
138.9
178.5
180.9
183.8
186.2
190.2
192.2
195.1
197.0
200.6
204.4
207.2
209.0
(209)
(210)
(222)
87
88
89
104
105
106
107
108
109
110
111
112
114
116
Fr
Ra
Ac
Rf
Db
Sg
Bh
Hs
Mt
Ds
Rg
Uub*
Uuq*
UUh*
(223)
(226)
(227)
(261)
(262)
(266)
(264)
(277)
(268)
(271)
(272)
(285)
(289)
(292)
Lanthanides
Actanides
58
59
60
61
62
63
64
65
66
67
68
69
70
71
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
140.1
140.9
144.2
(145)
150.4
152.0
157.3
158.9
162.5
164.9
167.3
168.9
173.0
175.0
103
90
91
92
93
94
95
96
97
98
99
100
101
102
Th
Pr
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
232.0
231.0
238.0
(237)
(244)
(243)
(247)
(247)
(251)
(252)
(257)
(258)
(259)
(262)