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GNC502S - GENERAL CHEMISTRY 1B -1ST OPP - NOV 2022 |
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n Am I BI A u n IVER s ITY
OF SCIEnCE Ano TECHnOLOGY
FACULTYOF HEALTH,NATURALRESOURCESAND APPLIEDSCIENCES
DEPARTMENT OF NATURAL AND APPLIED SCIENCES
QUALIFICATION: BACHELOROF SCIENCE
QUALIFICATION CODE: 07BOSC
LEVEL: 5
COURSE CODE: GNC502S
COURSE NAME: GENERALCHEMISTRY1B
SESSION: NOVEMBER 2022
PAPER: THEORY
DURATION: 3 HOURS
MARKS: 100
FIRSTOPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S)
DR. EUODIA HESS
DR. MARIUS MUTORWA
MODERATOR: DR. JULIEN LUSILAO
INSTRUCTIONS
1. Answer ALL the questions.
2. Write clearly and neatly.
3. Number the answers clearly
4. All written work must be done in blue or black ink and sketches can
be done in pencil
5. No books, notes and other additional aids are allowed
PERMISSABLE MATERIALS
Non-programmable calculators
ATTACHMENTS
1. List of useful constants
2. Periodic Table
THIS QUESTION PAPER CONSISTS OF 10 PAGES
(Including this front page, list of constants and periodic table)
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SECTIONA
QUESTION 1: Multiple Choice Questions
• There are 20 multiple choice questions in this section. Each question carries
3 marks. Answer ALL questions by selecting the letter of the correct answer.
• Choose the best possible answer for each question, even if you think there is
another possible answer that is not given.
[60]
[60]
1. Which statement concerning relative rates of reaction is correct for the chemical equation
given below?
A. The rate of disappearance of CH30H is equal to the rate of disappearance of 02
B. The rate of disappearance of CH30H is two times the rate of appearance of H20
C. The rate of disappearance of CH30H is half the rate of appearance of CO2
D. The rate of appearance of H20 is two times the rate of appearance of CO2
E. The rate of appearance of H20 is four times the rate of disappearance of CH30H
2. The average rate of disappearance of ozone in the following reaction is found to be
8.93 x 10-3 atm/s
2 03 (g) 02 (g)
What is the rate of appearance of 02 during this interval?
A. 5.95 x 10-3 atm/s
B. 8.93 x 10-3 atm/s
C. 26.6 x 10-3 atm/s
D. 356 x 10-3 atm/s
E. 13.4 x 10-3 atm/s
3. The rate law for a reaction is rate= k[A]2[B]. Which of the following mixtures of reactants
will give the smallest initial rate?
A. 1.0 MA, 1.0 MB
B. 2.0 M A, 0.50 M B
C. 0.50 M A, 0.50 M B
D. 0.125 M A, 3.0 M B
E. 1.5 M A, 0.50 M B
4. If 35.0 g H20 at 22.7 °C is combined with 65.0 g H20 at 87.5 °C, what is the final temperature
of the mixture? The specific heat capacity of water is 4.184 J/g·K
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A. 25.1 °C
B. 45.4 °C
C. 50.8 °C
D. 64.8 °C
E. 48.9 °
5. How much energy is gained by copper when 48. 7 g of copper is warmed from 10.2 °C to
67.0 °C?The specific heat capacity of copper is 0.385 J/(g•0 C).
A. 1.91 X 102J
B. 25.79 J
C. 21.86 J
D. 1.06 X 103 J
E. 1.26 X 103
6. Which of the following statements is/are CORRECT?
A. A system is defined as an object or collection of objects being studied
B. Surroundings are defined as the entire universe, including the system
C. In an endothermic reaction, heat is transferred from the system to the surroundings
D. A and B
E. None of the above
7. Which of the following statements is/are CORRECT?
A. For a chemical system, if the reaction quotient (Q} is greater than K, reactant must be
converted to products to reach equilibrium
B. For a chemical system at equilibrium, the forward and reverse rates of reaction are
equal
C. For a chemical system at equilibrium, the concentrations of products divided by the
concentrations of reactants equals one.
D. C and B
E. None of the above
8. For the reaction 2NO(g} + O2(g} 2NO2(g} at 750°C, what is the relationship between Kc
and Kp?
A. Kc= Kp
B. Kc= KpX (Rn- 1
C. Kc= Kp= 1.0
D. Kc= KpX (RD¼
E. Kc= KpX (RD1
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9. Ozone is formed from oxygen: 3 O2(g);:=2 O3(g). Calculate the value of Kp,given that
Kc= 2.5 x 10- 29at 298 K.
A. 1.0 X 10-3o
B. 2.1 X 10-30
C. 2.5 X 10- 29
D. 3.3 X 10- 2B
E. 6.1 x10- 28
10. Which of the following ground-state electron configurations corresponds to an atom that
has the most negative value of the electron affinity?
A. ls 22s22p63s1
B. ls 22s22p63s23p5
C. ls 22s22p63s23p 2
D. ls 22s22p 63s23p63d54s2
E. ls 22s22p6
11. The statement that the first ionization energy for an oxygen atom is lower than the first
ionization energy for a nitrogen atom is
A. inconsistent with the general trend relating changes in ionization energy across a period
from left to right and due to the fact that oxygen has one doubly occupied 2p orbital and
nitrogen does not.
B. consistent with the general trend relating changes in ionization energy across a period
from left to right because it is harder to take an electron from an oxygen atom than from a
nitrogen atom.
C. consistent with the general trend relating changes in ionization energy across a period
from left to right because it is easier to take an electron from an oxygen atom than from a
nitrogen atom.
D. incorrect.
E. inconsistent with the general trend relating changes in ionization energy across a period
from left to right and due to the fact that the oxygen atom has two doubly occupied 2p
orbitals and nitrogen has only one.
12. What is the ground-state electron configuration of terbium (Tb)?
A. ls 22s22p63s23p63d 104s24p 64d 10Ss25p6Sd96s2
B. ls 22s22p63s23p63d 104s24p 64d 104f14Ss2Sp3
C. ls 22s22p63s23p 63d 104s24p 64d 10Ss2Sp6Sd106s1
D. ls 22s22p 63s23p63d 104s24p64d 104f9Ss25p66s2
E. ls 22s22p63s23p 63d 104s24p 64d94f 105s2Sp66s2
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13. In the Lewis dot formula that minimizes formal charge, how many bonds are there in the
tetrathionate ion, S4052-7
A. 7
B.9
C. 15
D. 11
E. 13
14. Which of the following bonds would be the least polar yet still be considered polar
covalent?
A. Mg-0
B. C-0
C. Si-0
0.0-0
E. N-0
15. When the cations Na+, K+,Rb+,cs+ are combined with chloride ion in the gas phase to form
ion pairs, which pair formation releases the greatest amount of energy?
A. KCI
B. All release the same amount of energy.
C. RbCI
D. NaCl
E. CsCI
16. How many valence electrons are there in the acetate ion (the conjugate base of acetic acid)?
A.22
B.23
C.24
D.36
E.38
17. Which of the following statements concerning Lewis electron-dot formulae is/are correct?
1. A Lewis electron-dot formula (Lewis structure) is identical to a structural formula.
2. The skeleton of a molecule need not be known to draw the correct Lewis electron-
dot structure.
3. Lewis electron-dot formulae show the location of bonding and nonbonding
electrons in three dimensional space.
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A. 1 only
B. 2 only
C. 3 only
D. all the statements are correct
E. none of the above statements are correct
18. What is the C-C-H bond angle in H2CCO?
A. 109°
B. 180°
C. 120°
D. 144°
E. 90°
19. Which of the following statements correctly describes the reaction of BF3with NH3to form
F3B-NH3?
A. Both nitrogen and boron change from trigonal planar to tetrahedral geometry during the
reaction.
B. Boron changes from trigonal planar to tetrahedral geometry during the reaction.
C. There are no changes in the formal charge on any atom during the reaction.
D. Nitrogen changes from trigonal planar to tetrahedral geometry during the reaction.
E. There is no change in geometry around the nitrogen or boron atoms.
20. Which of the following concerning sand p bonds is/are correct?
1. A sigma bond may be formed from the sideways overlap of two parallel p orbitals.
2. No more than two pi bonds are possible between adjacent carbon atoms.
3. The considerable energy required to rotate pi bonded atoms is the primary reason
for geometrical isomerism in some pi bonded molecules.
A. 1 only
B. 2 only
C. 3 only
D. 1 and 2
E. 2 and 3
END OF SECTIONA
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SECTIONB:
[40]
There are FIVE questions in this section. Answer all questions. Show clearly, where necessary,
how you arrive at the answer as all working will carry marks.
QUESTION 1
[G]
Consider the following reaction:
NO2+ 02 (g} N2Os(g}
At a particular moment during the reaction, molecular oxygen is reacting at a rate of 0.024 M/s.
a} At what rate is N2Osbeing formed?
(3)
b} At what rate is NO2 reacting?
(3)
QUESTION 2
[6]
At the start of a reaction there are 0.249 mol N2,3.21x10· 2 mol of H2and 6.42x10· 4 mol NH3
In a 3.50 L reaction vessel at 375 °C. If Kc is 1.2 at this temperature, decide whether the system
Is at equilibrium.
QUESTION 3
[8]
Calculate the standard enthalpy of formation of CO from the oxidation of carbon:
C (g} + 02 (g} CO (g}
a} CO (g} + ½ 02 CO2(g} tirH 01 = - 283.0 kJ/mol-rxn
b} C (s} + 02 (g} CO2(g} tirH 01 = - 393.5 kJ/mol-rxn
QUESTION 4
[10]
What is the electron domain geometry and orbital hybridization for the central atom in each of the
following molecule or ions? Each question below carries two marks.
a} AICl4•
b} Pentachloride phosphorous
c} Xenon difluoride
d} XeOF2
e} O2SF2
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QUESTION 5
(10]
The lactic acid molecule, CH3CH(OH)COOHg,ives sour milk its unpleasant, sour taste.
a) Draw the Lewis structure for the molecule, assuming carbon always forms four bonds
in its stable compounds.
(4)
b) How many n:and o bonds are in the molecule?
(2)
c) What is the hybridization of atomic orbitals around the carbon atom associated with
the shortest bond in the molecule?
(2)
d) What is the bond angle around the carbon atom associated with the shortest bond in
the molecule?
(2)
END OF EXAMINATION
GOODLUCK
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USEFULCONSTANTS
Gas constant, R = 8.3145 J · mo1-1 · K-1 = 0.083145 dm 3 · bar· mol- 1 · K-1 = 0.08206 L atm mo1-1 · K-1
1 Pa · m3 = 1 kPa.L = 1 N · m = 1 J
1 atm = 101 325 Pa = 760 mm Hg= 760 torr
Avogadro's Number, NA= 6.022 x 1023 mo1-1
Planck's constant, h = 6.626 x 10-34 Js
Speed of light, c = 2.998 x 108 ms-1
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PERIODIC TABLE OF THE ELEMENTS
18
l
2
H
1.00794 2
13
14
IS
He
16
17 4.00260
34
5
6
7
8 9 10
Li Be
B C N 0 F Ne
6.941 9.01218
10.81 12.011 14.0067 15.9994 18.9984 20.179
11 12
13 14 15 16 17 18
Na Mg
Al Si p s Cl Ar
22.9898 24.305 3
4
5
6
7
8
9
10
II
12 26.9815 28.0855 30.9738 32.06 35.453 39.948
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
39.0983 40.08 44.9559 47.88 50.9415 51.996 54.9380 55.847 58.9332 58.69 63.546 6538 69.72 72.59 74.9216 78.96 79.904 83.8
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
"'tJ
DJ
O'O
rt)
...0
-0...
Rb Sr y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
85.4678 87.62 88.9059 91.22 92.9064 95.94 (98) 101.07 102.906 106.42 107.868 112.41 114.82 118.69 121.75 127.6 126.9 131.29
55 56 71 72 73 74 75 76
Cs Ba Lu Hf Ta w Re Os
77 78 79 80 81 82
Ir Pt Au Hg Tl Pb
83 84 85 86
Bi Po At Rn
0
132.905 137.33 174.967 178.49 180.948 183.85 186.207 190.2 192.22 195.08 196.967 200.59 204.383 207.2 208.908 (209) (210) (222)
87 88 103 104 105 106 107 108 109 110 111 112
114
116
118
Fr Ra Lr Rf Db Sg Bh Hs Mt Uun Uuu Uub
Uuq
(223) 226.025 (260) (261) (262) (263) (264) (265) (268) (269) (272) (269)
Uuh
Uuo
Lanthanides: 57 58 59 60 61 62 63 64 65 66 67 68 69 70
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
138.906 140.12 140.908 144.24 (145) 150.36 151.96 I 57.25 158.925 162.50 161.930 167.26 166.934 173.04
Actinides:
89 90 91 92 93 94 95 96 97 98 99 100 101 102
u Ac Th Pa
Np Pu Am .Cm Bk Cf Es Fm Md No
227.028 232.038 231.036 238.029 237.048 (244) (243) (247) (247} (251) (252) (257) (258) (259)