Download June 01, 2008

School of Chemistry
UNIVERSITY OF KWAZULU-NATAL
JUNE 2008 EXAMINATION
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
DURATION : 3 HOURS
TOTAL MARKS : 100
External Examiner: Dr C Southway
University of KwaZulu-Natal, Pietermaritzburg
Internal Examiner: Mrs R Moodley, Ms T Naicker, Ms R Robb
University of KwaZulu-Natal, Westville
Mr M Rasalavavho
University of KwaZulu-Natal, Pietermaritzburg
Instructions to Candidates:

This paper consists of 12 pages including a Periodic Table and a Table of
Relative Atomic Masses. Please check that you have them all.

Answer all 5 questions on the paper provided and show your working clearly.

Marks are given in brackets after each question and all questions are marked
out of 20.
QUESTION ONE
1.1
Select from the table below the formula/word/phrase that best matches the
following statements or definitions a) to j)
Note:

The formula/word/phrase can be used more than once or not at all in the
answers.

Some questions may have more than one answer or no answer, in which case
you will write ‘No answer’

The mark will only be awarded if the complete answer is provided.
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
KBr
Solubility
Conductivity
Liquid
Diffusion
Volatile
Solid
HF
Sr(OH)2
Ar
Compressibility
Fe/V
Li2O
Boiling point
CO
Mass
a)
Acetone has a high vapour pressure and therefore evaporates readily
b)
Contains the most reactive halogen
c)
Macroscopic properties of matter
d)
An inert gas
e)
Classified as a mixture
f)
Molecule/s
g)
Formula Units
h)
Pure substance
i)
Contains an alkali metal
j)
Matter having a fixed shape
(10)
1.2
Camphor is an organic compound which is used in some mothballs.
At room
temperature this solid compound vapourises. This process is known as
sublimation.
a)
Give another example of a substance which undergoes this process.
(1)
b)
What is the reverse transition/process called?
(1)
c)
Explain the process of sublimation with the help of the kinetic
(particulate) theory of matter, using camphor as an example.
(4)
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
1.3
Classify the following as physical (quantitative or qualitative) or chemical
properties. Give a reason for your answer.
a)
Silver jewellery turns black due to continuous exposure to air.
(1)
b)
The molecule hexane is a colourless liquid at 25 °C.
(1)
c)
At 20 °C, 37 g of NH4Cl is soluble in 100 g of H2O.
(1)
d)
Zinc reacts with hydrochloric acid solution to produce hydrogen gas and
a water solution of zinc chloride.
(1)
[20]
QUESTION TWO
2.1
Select from the table the formula/word/phrase that best matches the following
statements a) to h)
Note:

The formula/word/phrase can be used more than once or not at all in
answering the question.

Some questions may have more than one answer or no answer, in which
case you will write ‘No answer’

The mark will only be awarded if the complete answer is provided.
3
School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
Mixture
Sterling silver
KMnO4 (aq)
Chemical change
Brass
Concrete
Closed system
Isolated system
Physical change
Endothermic
Exothermic
Glass
a)
Examples of homogeneous mixtures.
b)
An alloy.
c)
When 2 colourless solutions are mixed together a blood red solution
forms.
d)
The reaction that has heat as a product.
e)
A closed thermos bottle or flask.
f)
The transformation that occurs when a lump of iron is stretched into a
wire.
g)
The reaction whereby the energy of the products is higher than that of
the reactants.
h)
The type of change(s) that obeys the Law of Conservation of Mass.
(8)
2.2
As a chemist working in the forensics department of the SAPS, you were called
upon to identify an unknown powder that was found at 3 different crime
scenes. Your preliminary examination of the powder samples obtained from
Scene 1 and Scene 2 might suggest it being an illegal drug (a date-rape drug).
However, you were uncertain about the powder found at Scene 3. After
separating the powder into its elements, you obtain the data presented in the
table below.
Scene Mass of Sample (g) Mass of C (g) Mass of H (g) Mass of N (g) Mass of O (g)
1
94.46
72.07
4.800
11.19
6.403
2
24.97
19.05
1.268
2.960
1.693
3
29.30
21.60
1.500
1.400
4.800
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
a)
State the Law of Constant Composition.
(2)
b)
Explain, using calculations, how you could use the data above to show
that the powder found at Scene 1 could be the same compound as the
powder found at Scene 2 .
(5)
c)
Calculate the mass of carbon that would be found in a sample that
contains 45.67 g of oxygen.
(3)
d)
Explain, without using calculations, how you could possibly use the data
above to verify that the substance found at Scene 3 is not the same
compound.
(2)
[20]
QUESTION 3
3.1
When octane (C8H18) vapour undergoes combustion (reacts with oxygen) in
the car engine, water vapour and carbon dioxide are produced.
a)
Write a word equation for this reaction.
(1)
b)
Write a balanced chemical equation for the reaction including state
symbols.
(2)
c)
State whether the enthalpy change, ∆H, for the above reaction is
positive or negative AND give a reason for your answer.
(1)
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
d)
Explain how you could test for the carbon-containing gas liberated AND
provide a chemical equation as part of you explanation.
(2)
3.2
Classify the chemical reactions below by selecting the term(s) from the table
below that best matches with the reactions a) to d).
Note:

The term can be used more than once or not at all in answering the reactions.

Some reactions may have more than one answer or no answer, in which case
you will write ‘No answer’

The mark will only be awarded if the complete answer is provided.
Combination reaction
Displacement reaction
Synthesis reaction
Neutralisation reaction
Precipitation reaction
Gas forming reaction
Decomposition reaction
Combustion reaction
Dehydration reaction
a)
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
b)
2Hg (l) + O2 (g)  2HgO (s)
c)
PbCl2 (aq) + CuSO4 (aq)  PbSO4 (s) + CuCl2 (aq)
d)
2H2O2 (aq)  2H2O (l) + O2 (g)
(4)
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
3.3
The graph shows the solubility curves for several substances. Answer the
following questions based on the graph.
a)
Which substance is the most soluble at 60oC?
(½)
b)
Which substance is the least soluble at 10oC?
(½)
c)
Define the term saturated solution.
(1)
d)
If 45 g of ammonia gas (NH3) was dissolved in 100 g of water at 20oC,
would the solution be unsaturated, saturated or supersaturated?
Explain your answer?
(2)
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
e)
What mass of ammonium chloride (NH4Cl) will precipitate out of 250 g
saturated NH4Cl solution it is cooled from 90oC to 50oC?
(3)
f)
How much more KNO3 would need to be added to make the solution
saturated if 108 g of solution, containing 20 g of the salt, is heated to
50oC?
(4)
[20]
QUESTION 4
A 250.0 ml solution of potassium dichromate (Solution A), was prepared in the
laboratory by dissolving 31.25 g of the salt (K2Cr2O7) in water.
4.1
Explain clearly how you would go about preparing this solution in the
laboratory.
(2)
4.2
Calculate the concentration of Solution A in g/dm3.
(3)
4.3
Determine how many milliliters of water was added to Solution A if the density
of Solution A is 1.02 g/ml. (Density of water = 1.00 g/ml).
(3.5)
4.4
Would you consider this to be a concentrated solution or a dilute solution?
Explain your answer.
(2)
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
4.5
How many milliliters of water would need to be added to 90 ml of Solution A to
decrease the concentration to 69.44 g/dm3?
(3.5)
4.6
If a mass of 8.75 g of K2Cr2O7 was added to Solution A and the volume
increased by 3.27 ml, what would the concentration of the new solution be in
g/ml?
(3)
4.7
Determine the volume in milliliters of Solution A needed to make 100 ml of
Solution B with a concentration of 9.54 g/dm3.
(3)
[20]
QUESTION 5
5.1
Name each of the pieces of laboratory apparatus, A to L, shown below.
NOTE: Half a mark will only be awarded if the full name of the apparatus is
given.
(6)
100 ml
100 ml
150 ml
250 ml
A
5.2
B
C
D
E
F
G
H
I
J
K
L
Give the letter(s) identifying the picture(s) for each answer. NOTE: The
letters A to L can be used more than once in answering questions a) to f).
Some questions have more than one answer and some may have no answer.
Each question a) to f) is worth one mark.
The mark will be assigned only if the complete answer is given.
Which of the above A to L:
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
a)
has a single graduation mark?
b)
is used in a distillation experiment?
c)
can be used to measure out variable volumes of a liquid?
d)
is used in an experiment to separate out a mixture of two immiscible
liquids?
e)
is used in a filtration experiment?
f)
has a tap which controls the outflow of liquid?
(6)
5.3
Correct the following statements without using the word “NOT”. Your correct
statement should include all the underlined words.
a)
Simple distillation is preferred to use when separating liquids with
boiling points close to each other. In such a case a fractionating column
should be attached to the mouth of the collecting container/receiver.
(2)
b)
Differential measuring, also known as measuring directly, is preferred.
For this method, students are required to tare/zero the mass balance
before adding sample to the container.
(2)
c)
During a physical change, the composition of the reactants change and
their masses often increase.
(2)
d)
The least unit of measurement gives the maximum volume glassware
can hold and is determined by taking a reading at the bottom of the
meniscus of the liquid contained.
(2)
[20]
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School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, WESTVILLE
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
11
School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, WESTVILLE
CHEM099/CHEM199 : FOUNDATION CHEMISTRY
JUNE 2008 EXAMINATION
TABLE OF RELATIVE ATOMIC MASSES (Based on Carbon-12)
Symbol
Actinium
Aluminium
Americium
Antimony
Argon
Arsenic
Astatine
Barium
Berkelium
Beryllium
Bismuth
Boron
Bromine
Cadmium
Caesium
Calcium
Californium
Carbon
Cerium
Chlorine
Chromium
Cobalt
Copper
Curium
Dysprosium
Einsteinium
Erbium
Europium
Fermium
Fluorine
Francium
Gadolinium
Gallium
Germanium
Gold
Hafnium
Helium
Holmium
Hydrogen
Indium
Iodine
Indium
Iron
Krypton
Lanthanum
Lawrencium
Lead
Lithium
Lutetium
Magnesium
Manganese
Mendelevium
Ac
Al
Am
Sb
Ar
As
At
Ba
Bk
Be
Bi
B
Br
Cd
Cs
Ca
Cf
C
Ce
CI
Cr
Co
Cu
Cm
Dy
Es
Er
Eu
Fm
F
Fr
Gd
Ga
Ge
Au
Hf
He
Ho
H
In
I
Ir
Fe
Kr
La
Lr
Pb
Li
Lu
Mg
Mn
Md
Atomic
No.
89
13
95
51
18
33
85
56
97
4
83
5
35
48
55
20
98
6
58
17
24
27
29
96
66
99
68
63
100
9
87
64
31
32
79
72
2
67
1
49
53
77
26
36
57
103
82
3
71
12
25
101
Atomic
Mass
[227]
26.98
[243]
121.75
39.95
74.92
[210]
137.34
[247]
9.012
208.98
10.81
79.90
112.41
132.91
40.08
[251]
12.01
140.12
35.45
52.00
58.93
63.55
[247]
162.50
[252]
167.26
151.96
[257]
19.00
[223]
157.25
69.72
72.61
196.97
178.49
4.00
164.93
1.01
114.82
126.90
192.22
55.85
83.60
138.91
[260]
207.2
6.94
174.97
24.31
54.94
[258]
Symbol
Mercury
Molybdenum
Neodymium
Neon
Neptunium
Nickel
Niobium
Nitrogen
Nobelium
Osmium
Oxygen
Palladium
Phosphorus
Platinum
Promethium
Plutonium
Polonium
Potassium
Praseodymium
Proctactinium
Radium
Radon
Rhenium
Rhodium
Rubidium
Ruthenium
Samarium
Scandium
Selenium
Silicon
Silver
Sodium
Strontium
Sulfur
Tantalum
Technetium
Tellurium
Terbium
Thallium
Thorium
Thulium
Tin
Titanium
Tungsten
Uranium
Vanadium
Xenon
Ytterbium
Yttriium
Zinc
Zirconium
Hg
Mo
Nd
Ne
Np
Ni
Nb
N
No
Os
O
Pd
P
Pt
Pm
Pu
Po
K
Pr
Pa
Ra
Rn
Re
Rh
Rb
Ru
Sm
Sc
Se
Si
Ag
Na
Sr
S
Ta
Tc
Te
Tb
Tl
Th
Tm
Sn
Ti
W
U
V
Xe
Yb
Y
Zn
Zr
A value given in brackets denotes the mass of the longest-lived or best known isotope
12
Atomic
No.
80
42
60
10
93
28
41
7
102
76
8
46
15
78
61
94
84
19
59
91
88
86
75
45
37
44
62
21
34
14
47
11
38
16
73
43
52
65
81
90
69
50
22
74
92
23
54
70
39
30
40
Atomic
Mass
200.59
95.94
144.24
20.18
[237]
58.69
92.91
14.01
[259]
190.20
16.00
106.42
30.97
195.08
[147]
[244]
[209]
39.10
140.91
231.04
226.03
[222]
186.21
102.91
85.47
101.07
150.36
44.96
78.96
28.09
107.87
22.99
87.62
32.07
180.95
[98]
127.60
158.93
204.37
232.04
168.93
118.71
47.88
183.85
238.03
50.94
131.29
173.04
88.91
65.39
91.22