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GNC502S-GENERAL CHEMISTRY 1B-JAN 2020 |
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p
NAMIBIA UNIVERSITY
OF SCIENCE AND TECHNOLOGY
FACULTY OF HEALTH AND APPLIED SCIENCES
DEPARTMENT OF NATURAL AND APPLIED SCIENCES
QUALIFICATION: BACHELOR OF SCIENCE
QUALIFICATION CODE: 07BOSC
COURSE NAME: GENERAL CHEMISTRY 1B
SESSION: JANUARY 2020
DURATION: 3 HOURS
LEVEL: 5
COURSE CODE: GNC502S
PAPER: THEORY
MARKS: 100
SUPPLEMENTARY/SECOND OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S) | DR. EUODIA HESS
DR. MARIUS MUTORWA
MODERATOR: | DR. JULIEN LUSILAO
INSTRUCTIONS
Answer ALL the questions.
Write clearly and neatly.
Number the answers clearly
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
THIS QUESTION PAPER CONSISTS OF 12 PAGES (Including this front page and attachments)
Page 1 of 12
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SECTION A
[50]
QUESTION 1: Multiple Choice Questions
[50]
e There are 25 multiple choice questions in this section. Each question carries
2 marks.
e 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.
1. To which of the following causes could the slow rate of a chemical reaction be attributed to?
a low activation energy
. a high activation energy
the presence of a catalyst
. the temperature is high
the concentrations of the reactants are high
2. The steps below represent a proposed mechanism for the catalysed oxidation of CO by O3.
Step 1: NO2 (g) + CO (g) > NO (g) + CO2 (g)
Step 2: NO (g) + O3 (g) > NO2 (g) + O2 (g)
What are the overall products of the catalysed reaction?
CO2 and O2
NO and CO2
NO2 and O2
NO and O2
NO2 and CO2
3. The oxidation number of each chromium atom in Cr207* is:
A. +5
B. +6
C. +7
D. +12
E. None of the above
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4. In which of the following unbalanced reactions does chromium undergo oxidation?
A. Cr?* > Cr
B. Cr?* — Cr?*
C. Cr3* > Cr2077
D. None of the above
E. Cr3*> Cr?
5. For which of the following chemical changes does the heat of reaction (AH) correspond to
a heat of formation (AHformation)?
A. N (g) + 3 H (g) > NHs (g)
B. Nz (g+)3 H2 (g) > 2 NHs (g)
C. C(g)+O(g-)C
D. = No (g) + > He (g) > Ns (g)
E. None of the above
6. The pH of a 1.25 x 10° M NaOH solution is:
A 7.00
B 2.90
C 11.10
D 10.90
E 3.10
7. Which of the following describes the relationship between [H30*] and [OH-]?
A. [H30*][OH7] = 14.00
B. [H30*] + [OH] = 14.00
C. [H30*][OH-]=1.0x 104
D. [H30*] + [(OH~]=1.0x 104
E. None of the above
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8. A buffer solution was prepared by mixing 100 mL ofa 1.2M NH3 solution and 400 mL of
a 0.5M NH.,Cl solution. What is the pH of this buffer solution, assuming a final volume of
500 mL and Ky = 1.8 x 109?
A. 1.08
B. 4.96
C.5.8
D. 9.03
E.8
9. Which of the following is true regarding the relative molar rates of disappearance of the
reactants and the appearance of the products?
2NO (g) + 2H2 (g) > Na (g) + 2H20 (g)
|. N2 appears at the same rate that H2 disappears.
Il. H2O appears at the same rate that NO disappears.
Ill. NO disappears at the same rate that H2 disappears.
A.| only.
B. land Il only.
C. land III only.
D. Il and Ill only.
E. 1, Iland Ill
10. Write the appropriate equilibrium constant expression K; for the following reaction:
2CO(g) + O2(g) S 2CO2(g)
A. Ke = k[CO]2[02]
B. Ke = [CO2] / [CO] [02]
C. Ke= [CO]? [02] / [CO2]
D. Ke = [CO2]?/ [CO]? [02]
E. None of the above
11. Which two bonds are least similar in polarity?
A. Al-Cl and I-Br
B. O-F and CI-F
C. B-F and CI-F
D. I-Br and Si-Cl
E. C-Cl and Ge-Cl
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12. In the Lewis structure of HCO3-, the formal charge on H is
on Cis
A. -1,-1
B. 0,0
C.0,-1
D. +1, -1
E. -1, +1
and the formal charge
13. How many different types of resonance structures can be drawn for the ion S032- where all
atoms satisfy the octet rule?
A.1
B.2
G3
D.4
E.5
14. After drawing the Lewis dot structure of HOCIO2, pick the INCORRECT statement of the
following.
A. The oxygen bonded to the hydrogen has two lone pairs.
B. The oxygens not bonded to hydrogen have three lone pairs.
C. The O-Cl bonds are all double bonds.
D. The H-O bond is a single bond.
E. Chlorine has a full octet.
15. Which of the pairs of molecules below have the same hybridization on the central atom? (The
central atom is underlined in each molecule.)
A. CO2, CH4
B. H2CO, BeH2
C. BCI3, HNO
D. H20, HF
E. NH3, HNO
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“ O 16. Find the correct stereochemistry for the following alkenes:
JeHsK
Y
\\4
A
B
Cc
D
A. Ais Z, Bis Z, Cis £, Dis E
B. Ais Z, Bis E, Cis Z, Dis E
C.ABii s E,sCiE sZ,, Dis E
D.Ais E, Bis E, Cis Z, Dis Z
E. Ais Z, Bis Z, Cis E, DisZ
17. Which is the correct Lewis structure for acetic acid (CH3CO2H)?
HaH-O: g=0
HH
a)
A.a
B.b
C.c
D.d
E. none of the above
‘ik
"
H—-C—O—C-H
H
c)
18.For which of the structures below does carbon show the correct orbital hybridization?
H,C=O HC=CH,
CHy
HC=N
0O—C=0
sp
I
A. Il, Vand V
B. Il, Illand IV
C. I, land Il
D. I, Vand V
E. Il, Vand V
sp"
sp”
sp
sp
Il
I
IV
V
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19. Which of the following statements concerning lattice energy is incorrect?
A. MgO has a larger lattice energy than NaF.
B. The lattice energy for a solid with 2+ and 2—ions should be two times that for a solid
with 1+ and 1—ions.
C. MgO has a larger lattice energy than LiF.
D. Lattice energy is often defined as the change in energy that occurs when an ionic solid is
separated into isolated ions in the gas phase.
E. All of these are true.
20. Which of the following compounds has the most ionic bonding (i.e. has the highest percentage
of ionic character)?
CaF2
Lil
OF2
CsF
LiF
21. What is the C—C—H bond angle in H2CCO?
A. 109°
B. 180°
C. 120°
D. 90°
E. 45°
22. Which of the following statements is correct concerning the electron configuration [Ne]3s!3p1?
A It may represent a ground-state electron configuration of a Al* cation.
B It may represent an excited-state electron configuration of a Mg atom.
C. It may represent an excited-state electron configuration of a Ne~ anion.
D. It may represent a ground-state electron configuration of a Mg* cation.
E None of the above is correct
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23. Anonpolar bond will form between two
atoms of
different, opposite
identical, different
different, different
identical, equal
None of the above is correct
24. Which of the following compounds does not contain a C=O bond?
Ketones
Aldehydes
Esters
Ethers
All contain the C=O bond
25. Give the IUPAC name for the following structure.
electronegativity.
2-methyl-3-ethylheptane
3-ethyl-2methylheptane
5-isopropyloctane
4-isopropyloctane
2-methyl-3-propylheptane
END OF SECTIONA
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SECTION B:
[50]
QUESTION 1:
[5]
Assign the oxidation states for the underlined atom in each of the following:
a. NiO2
b. Fe30,
c. XeOF,
d. (NH4)2HPO,
e. CO
QUESTION 2:
[5]
A buffer solution contains 0.25 M NH3 (Kp = 1.8 x 10°) and 0.40 M NH.CI. Calculate the pH
of the solution.
QUESTION 3:
[10]
a. What are the factors affecting reaction rates?
(4)
b. Relate the rates for the disappearance of reactants and formation of products for the
following reaction:
(3)
PHs (g) — Pa (g) + H2(g)
c. Sucrose (Ci2H22011) decomposes to fructose and glucose in acid solution with rate law:
Rate = k[C12H22011]
k=0.216 h? at 25 °C
What is the half-life of sucrose at this temperature?
(3)
QUESTION 4:
[5]
NO: can exist in equilibrium with colourless gas N2Oz. Ke = 170 at 298K.
NOz (g) < N2Ou (g)
Suppose the concentration of NOz is 0.015 M and concentration of N20, is 0.025 M.
a. If the system is not in equilibrium, will Q be larger than, smaller than or equal to Kc?
(2)
b. In which direction will the reaction proceed to achieve equilibrium?
(3)
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QUESTION 5:
[9]
Consider the Lewis structure for ethyl acetate below, used as a solvent and aroma enhancer.
H :Q:
no
H—“i! “allc—é3 —¢—¢—|-H
H
HH
5.1 How many valence electrons are used to make the sigma bonds in the molecule?
(3)
5.2 What is the hybridization at each of the numbered atoms (i.e. C1, C2 and 03)?
(6)
QUESTION 6
[8]
Many classes of organic compounds undergo characteristic types of reactions.
Identify the type of organic reaction for the transformations below.
(8)
(a) CH3CHpBr + NaCN -—> CHgCH(o4 CNaNBr)
(b} (bon
AS.
catalyst
CY
4 H0)
"O.
oN
sleat
7Swe .
Nfpp
(d) C)
+ OyN—NO, Light _ on
( + HNO»)
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2 Pages 11-20 |
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QUESTION 7
[3]
Identify the functional groups in the following molecules.
(8)
a
~
(a) Cy
H
O
(c) nTJ
NH»
(C b) y OCH
Lf
O
(d)
0”I
THE END
GOODLUCK
USEFUL CONSTANTS:
Gas constant, R = 8.3145J: mol?: K2
= 0.083145 dm?: bar: mol: K1
= 0.08206 L atm mol: Kt
1Pa:m?=1kPa.l =1N'm =1)J
1 atm = 101 325 Pa = 760 mmHg = 760 torr
Avogadro’s Number, Na = 6.022 x 1023 mol
Planck’s constant, h = 6.626 x 1034 Js
Speed of light, c = 2.998 x 108 ms?
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