Download Final Exam - Dawson College

DAWSON COLLEGE
DEPARTMENT OF CHEMISTRY & CHEMICAL TECHNOLOGY
FINAL EXAMINATION CHEMISTRY 202-NYA-05
December 20, 2007
9:30 A.M. – 12:30 PM
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Student Number:____________________________
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INSTRUCTIONS:
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This exam set consists of 16 questions. Please ensure that your copy of this
examination is complete.
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Answer all questions in the space provided.
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1. Calculators may not be shared. Programmable calculators are not permitted.
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10.
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13.
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16.
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Significant
Figures
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Units
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TOTAL
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INSTRUCTORS: Please circle the name of your instructor:
J. Ali
D. Baril
O. Behar
H. Doan
I. Dionne
M. Di Stefano
M. Haniff
S. Harrison
H. Khouri
D. Montecalvo
S. Mutic
R. Squire
Y.-S. Uh
D. Vukadin
2. No books or extra paper are permitted.
3. In order to obtain full credit, you must show the method used to solve all
problems involving calculations and express your answers to the correct
number of significant figures.
4. Your attention is drawn to the College policy on cheating. This policy will
be enforced.
5. A Periodic Table is provided. You may detach the Periodic Table.
USEFUL DATA:
Avogadro’s Number NA = 6.022 x 1023 mol–1
Gas Constant
R
–1
= 2.178 x 10–18 J
7
–1
Rydberg Constant
RH = 1.0974 x 10 m
Planck’s Constant
h
= 6.626 x 10–34 J⋅s
Speed of light
c
= 2.998 x 108 m⋅s–1
Mass of an electron
me = 9.11 x 10–31 kg
Mass of a proton
mp = 1.67 x 10–27 kg
1 atm = 101.3 kPa = 760 mmHg = 760 torr
1 J = 1 kg⋅m2⋅s–2
–1
= 0.08206 L⋅atm⋅K ⋅mol = 8.314 L⋅kPa⋅K ⋅mol
= 8.314 J⋅K–1⋅mol–1
Bohr Orbit Constant B
–1
–1
Question 1
a. Write the formula of each of the following compounds.
i.
Dinitrogen monoxide
ii.
Copper (II) sulfate pentahydrate
iii.
Tin (IV) oxide
iv.
Phosphorous acid
v.
Ammonium hydrogen sulfate
b. Name each of the following compounds.
i.
MnS2
ii.
HClO4 (aq)
iii.
NH4C2H3O2
iv.
Li3N
v.
Na2O2
(2.5 marks)
(2.5 marks)
2
Question 2
Determine the empirical formula and the molecular formula of hydrogen tetrathionate
(226.3 g/mol) that gives the following mass percentages upon analysis:
H = 0.91%
Ans. empirical formula:
S = 56.67%
(6 marks)
O = 42.42%
Ans. molecular formula:
3
Question 3
(5 marks)
Limestone, CaCO3, reacts with hydrochloric acid to form calcium chloride, water and
carbon dioxide according to the following reaction:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
How many liters of CO2 gas will be formed at 755 torr and 33.0°C by the reaction of
2.35 g of limestone with an excess of hydrochloric acid? Assume 100% yield and that
the gas is ideal.
Ans. volume of CO2 gas formed:
4
Question 4
Cisplatin is an anticancer agent used for the treatment of solid
tumors such as in breast cancer and is prepared by reacting
potassium tetrachloroplatinate (K2PtCl4) and ammonia (NH3). The
other product generated is KCl.
Cisplatin
a. Write the balanced equation for this reaction
(1 mark)
If 10.00 g of potassium tetrachloroplatinate is mixed with 0.500 g of ammonia (NH3):
b. Identify the limiting reactant and calculate the theoretical yield.
Ans. Limiting reactant:
(4 marks)
Ans. theoretical yield:
c. If 3.52 g of Cisplatin is actually produced, what is the percent yield of Cisplatin?
(2 marks)
Ans. %yield of Cisplatin:
5
Question 5
a. Complete and balance the following molecular equation.
Fe(NO3)2 (aq)
+
NH4OH (aq)
(2 marks)
→
Give the physical state in brackets, ex: liquid = (l), for each of the substances
participating to the reaction.
Write also the complete ionic equation (C.I.E.), identify the spectator ions and
write the net ionic equation (N.I.E.) for this reaction.
(1.5 marks)
C.I.E.
Spectator ions:
N.I.E.
b. Classify each of the following reaction as:
precipitation,
acid-base
(1.5 marks)
or
oxidation-reduction (red-ox)
Chemical reaction
i
C6H12O6(s)
+
ii
Lead(II)
acetate(aq)
+
iii
6O2(g)
→
Classification
6CO2(g)
+
6H2O(g)
Sodium
Lead(II)
Sodium
→
+
sulfate(aq)
sulfate(s)
acetate(aq)
Copper(II)
+ Zinc metal →
Chloride(aq)
Cu(s)
+
ZnCl2(aq)
6
Question 6
a. Assign oxidation state (or oxidation numbers) to nitrogen in each of the
following compounds:
i. N2H4
iii. Na3N
ii. N2O3
iv. NO3
—
b. Balance the following oxidation-reduction reaction in an aqueous basic solution
using the half-reaction method.
—
ClO3 (aq) + N2H4(aq) →
(2 marks)
NO(g)
+
(3 marks)
—
Cl (aq)
Ans. balanced reaction:
c. Identify the substance being oxidized
(0.5 mark)
d. Identify the reducing agent
(0.5 mark)
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Question 7
a. Calculate the de Broglie wavelength (in meters) of a proton that is traveling at
25.0% of the speed of light.
(3 marks)
Ans. de Broglie wavelength:
b. One of the emission lines of the hydrogen atom has a wavelength of 656.3 nm.
i. In what region of the electromagnetic spectrum (ex: X-ray, UV, etc.) is this
emission line found?
(1 mark)
ii. Calculate the energy of the photon emitted by this transition.
(2 marks)
iii. Determine the initial or the final n value associated with this emission line if
one of the two energy levels is n = 2.
(2 marks)
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Question 8
a. Supply the missing quantum number(s) or sublevel names (or subshell):
n
l
i
ii
3
iii
ml
subshell
0
4p
(3 marks)
-2
0
2s
b. Consider the element with the ground-state electron configuration 1s22s22p4
c.
i. identify this element (name or atomic symbol)
(0.5 mark)
ii. write its electron configuration using the orbital diagram (box notation)
(0.5 mark)
Consider the atom chromium, Cr
i. Write its complete ground-state electron configuration
(0.5 mark)
ii. What is the number of unpaired electrons in Cr atom?
(0.5 mark)
d. Give the set of quantum numbers for the circled electron in the following orbital
diagram:
(1 mark)
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Question 9
(5 marks)
Indicate on this blank outline of a periodic table, which element is described by each of
the following. Place the letter of the question (a, b, c, etc) in the correct element box.
Messy answers will not be marked.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
Smallest atomic radius in Group 6A
Largest atomic radius in Period 6
Condensed ground-state electron configuration is [Ne] 3s23p2
The period 4 member whose (2-) ion is isoelectronic with Kr
A transition metal ion with a charge of 1+ having 5 unpaired “4d” electrons
The element with the highest first ionization energy in period 4
The excited electron configuration is 1s22s22p63s13p1
The halogen with the smallest electron affinity (less exothermic)
The noble gas with electrons occupying 4f orbitals
The least electronegative transition metal in period 5
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Question 10
a. Draw all the possible Lewis structures (resonance forms) for the following ion
with carbon as the central atom:
SCN
(3 marks)
—
b. Assign formal charges to each atom in each structure.
c. Indicate the most appropriate structure according to the formal charges?
(2 marks)
(1 mark)
11
Question 11
Complete the table below. For each of the following molecules:
a. Draw the Lewis structure. Also give the name of the electron-pairs arrangement.
b. Make a “3D”-sketch of the molecule with the bond angles and provide a name for
the molecular structure (or shape of the molecule)
Molecule
Lewis structure
with all the lone pairs
name of the electron-pairs arrangement
(9 marks)
3D-sketch (VSEPR)
with bond angles
Is this a polar
molecule?
name of the shape of the molecule
(Y / N)
PH3
BrF3
SO2
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Question 12
The structure for the amino acid methionine is given below.
a. Complete the structure by adding all missing lone pairs of electrons.
b. Complete the table for each of the atoms labeled 1 to 6. For each labeled atom,
give the hybridization, the bond angle and the number of σ and π bonds around
the atom.
Atom 1
Atom 2
Atom 3
Atom 4
Atom 5
(1 mark)
(6 marks)
Atom 6
Hybridization
Bond angle
no angle
Number of σ bonds
around the atom
Number of π bonds
around the atom
Question 13
a. Write the name of the most important intermolecular force that keeps the
following molecules in the liquid phase.
(3 marks)
i. CH3F
ii. H2O
iii. Br2
b. Arrange the following three substances in order of increasing boiling point.
HCl,
Low boiling point
<
HF,
(1 mark)
HBr
<
High boiling point
13
Question 14
a. Sketch the phase diagram for carbon dioxide (CO2) from the following data:
i. The triple point is at 5.2 atm, and –57°C
ii. The critical point is at 72.8 atm, and 31°C.
iii. At a pressure of 1 atm, the solid-gas phase transition takes place at –78°C
iv. At a pressure of 72.8 atm, the solid-liquid phase transition occurs at –21°C
(4 marks)
Don’t forget to label your axes and to indicate the phase (ex: g, l, s) in each region
From your phase diagram, answer the following questions:
b. For CO2 at 5 atm and —50°C, what is the stable phase present (gas, liquid, etc.)?
(1 mark)
c. What phase changes occur when the pressure of a sample of CO2 is decreased
from 70 atm to 7 atm at a constant temperature of 0°C ?
(1 mark)
14
Question 15
a. Calculate ΔH for the overall reaction:
4NO2(g)
using the following data
2N2O5(s)
2NO(g)
+
→
+
(4 marks)
O2(g)
4NO(g)
O2(g)
→ 2N2O5(s)
+
→
3O2(g)
2NO2(g)
ΔH = 447.4 kJ
ΔH = —114.2 kJ
Ans. ΔH overall reaction:
b. For the reaction below:
H⎯C≡N(g)
+
2H2(g)
→
(g)
ΔH = —158 kJ
Calculate the bond energy for the C≡N triple bond from the following data:
Bond
Bond energy
(kJ.mol-1)
H⎯H
432
C⎯H
413
C⎯N
305
N⎯H
391
(4 marks)
Ans. C≡N bond energy :
15
Question 16
You want to determine the Cu(II) concentration in an unknown solution by titration.
You will first precipitate Cu2+ from the solution by adding an excess of iodide ion
Cu2+(aq) +
—
I (aq) →
CuI(s) + I2(aq)
(5 marks)
[unbalanced]
The corresponding amount of iodine (I2) formed will then be titrated with a sodium
thiosulfate solution:
—
S2O32-(aq) + I2(aq) → S4O62-(aq) + I (aq)
[unbalanced]
The end-point of the titration is reached when all the I2 has reacted. At this point, the
violet starch indicator has turned white. Use the following values from the laboratory
data sheet to calculate the concentration of Cu2+ in the unknown.
Fill-in the blanks
Volumetric analysis of Cu2+
DATA SHEET
a. Write the overall stoichiometric equation
b. Results and observations
Unknown no: 20
Concentration of the standard Na2S2O3 solution, M
0.0206
Initial burette reading, mL
Final burette reading (mL)
Volume of Na2S2O3 used (mL)
Number of mole of Na2S2O3 used
Number of mole of Cu2+ in the unknown sample
Volume of the original Cu2+ solution used (mL)
Concentration of the Cu2+ in the original solution (M)
0.17
9.82
10.00
(from a 10 mL pipette)
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Periodic Table of the Elements
1A
8A
1
2
1 H
He
1.008 2A
3
4
2 Li Be
6.9419.012
11
12
22.9924.31 3B
4B
5B
22
4 K Ca Sc Ti
20
4A
5A
6A
7A
4.003
5
6
7
8
9
10
B
C
N
O
F
Ne
10.8112.0114.0116.0019.0020.18
3 Na Mg
19
3A
21
13
14
15
16
17
18
Al
Si
P
S
Cl Ar
26.9828.0930.9732.0735.4539.95
6B
7B
8B
9B
10B
1B
2B
23
24
25
26
27
28
29
30
V
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
31
32
33
34
35
36
39.1040.0844.9647.8750.9452.0054.9455.8558.9358.6963.5565.3969.7272.6174.9278.9679.9083.80
38
39
40
5 Rb Sr
37
Y
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
41
42
43
44
45
46
47
48
49
50
51
52
53
54
I
Xe
85.4787.6288.9191.2292.9195.9498.00101.1102.9106.4107.9112.4114.8118.7121.8127.6126.9131.3
76
77
78
6 Cs Ba La* Hf Ta W Re Os
55
56
57
72
73
74
75
Ir
Pt Au Hg Tl Pb Bi Po At Rn
79
80
81
82
83
84
85
86
132.9137.3138.9178.5181.0183.8186.2190.2192.2195.1197.0200.6204.4207.2209.0209.0210.0222.0
87
88
89 104 105 106 107 108 109 110 111 112
7 Fr Ra Acª Rf Db Sg Bh Hs Mt Uun Uuu Uub
= metalloid
223.0226.0227.0261.0262.0263.0262.0265.0266.0269.0272.0277.0
58
*Lanthanides
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
140 141 144 145 150 152 157 159 163 165 167 169 173 175
90
ªActinides
91
92
93
94
95
96
97
98
99 100 101 102 103
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
232 231 238 237.1 244 243 247 247 251 252 257 258 259 260
17