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ICH401S - INTRODUCTION TO CHEMISTRY A - 2ND OPP - JAN 2020 |
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1 Pages 1-10 |
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1.1 Page 1 |
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NAMIBIA UNIVERSITY
OF SCIENCE AND TECHNOLOGY
FACULTY OF ENGINEERING
InSTEM
QUALIFICATION: INTRODUCTION TO SCIENCE, TECHNOLOGY, ENGINEERING AND MATHEMATICS
QUALIFICATION CODE: O4STEM
LEVEL: 4
COURSE CODE: ICH401S
COURSE NAME: INTRODUCTION TO CHEMISTRY A
SESSION:
JANUARY 2020
PAPER:
N/A
DURATION:
3 HOURS
MARKS:
100
SECOND OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S)
Mr Victor Uzoma
MODERATOR:
Prof Habauka M Kwaambwa
INSTRUCTIONS
Answer all questions.
Write all the answers in ink.
No books, notes, correction fluid (Tippex) or cell phones allowed.
Pocket calculators are allowed.
You are not allowed to borrow or lend any equipment or stationary.
All FINAL ANSWERS must be rounded off to TWO DECIMAL PLACES unless otherwise
stated.
7. Periodic table on page 10.
THIS QUESTION PAPER CONSISTS OF 10 PAGES (Excluding this front page)
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1.2 Page 2 |
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Question 1
[9]
1.1
Name the techniques, which are suitable for separating the following mixture:
(3)
Situation
Petrol from crude oil
Pure sugar from a solution
Two immiscible liquids
Separation Technique
1.2 The diagram below shows the chromatography paper from an experiment that
has been analysed and four pigments identified. The centre of each pigment is
marked and the colour labelled.
solvent front ««— ee wwe Orange pi/ gment
| omm yellow pigment
| me green-blue pigment
«mee green-yellow pigment
STAFTE HS secer
| ewe green-brown pigment
1.2.1 Find the R-value for each pigment on the diagram:
(4)
Orange
Yellow
Green-Blue
Green-Yellow
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1.3 Page 3 |
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1.2.2 The table below shows Reference Ry values:
Pigment
Carotene
Xanthopll
Chlorophy A
Chlorophyl B
Rr Value
0.94
0.89
0.46
9.22
Identify the four pigments as best you can using the reference Rf values.
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1.4 Page 4 |
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Question 2
[11]
Titanium and vanadium are consecutive elements in the first transition metal series.
2.1
Describe the bonding in metals.
(1)
2.2 Titanium exists as several isotopes. The mass spectrum of a sample of titanium
gave the following data:
Mass number,
46
47
48
49
50
% abundance
7.98
7.32
73.99
5.46
§.25
Calculate the relative atomic mass of titanium to two decimal places.
(2)
2.3. State the number of protons, neutrons and electrons in the 487i atom.
(1)
2.4.1 State the full electron configuration of the $87i2* ion.
(3)
2.4.2 Suggest why the melting point of vanadium is higher than that of titanium.
(1)
2.4.3. Vanadium and titanium can form metal complexes with ligands. Describe, in
terms of the electrons involved, how the bond between a ligand and a central
metal ion is formed.
(1)
2.5.1 State the type of bonding in potassium chloride, which melts at 1043 K.
(1)
2.5.2 Achloride of titanium, TiCl4, melts at 248 K. Suggest why the melting point is so
much lower than that of KCI.
(1)
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Question 3
[11]
Hydrogen sulfide, given off by decaying organic matter, is converted to sulfur dioxide
in the atmosphere by the reaction:
2H2S(g) + 302g) —> 2S02(g) + 2H20(/)
3.1
How many moles of H2S are required to form 8.20 moles of SO2?
3.2
How many grams of O2 are required to react with 1.00 mole of H2S?
(2)
3.3
How many grams of water are produced from 6.82 g H2S?
(2)
3.4
If 12.0 grams of SO2 are formed from 7.98 g of H2S, what is the percent yield?
(3)
3.5
How many grams of SO2 are produced starting from 2.66 g H2S and 3.00 g O2?
Which reactant is the limiting reagent?
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Question 4
[6]
Calcium carbonate reacts with dilute hydrochloric acid:
CaCO3(s) + 2HC/(aq) > CaCl2(aq) + CO2(g) + H2O(1)
A student investigated this reaction by measuring the volume of carbon dioxide released
every minute at constant temperature.
4.1
Draw a diagram of the apparatus that the student could use to investigate this
reaction.
(2)
4.2 The graph shows the results of this reaction using three samples of calcium
carbonate of the same mass: large pieces, medium-sized pieces and small pieces.
volume of
carbon dioxide
fom
50
1
150
2
time/s
4.2.1 Which sample, large, medium or small pieces, gave the fastest initial rate of
reaction?
(1)
4.2.2 The experiment was repeated using powdered calcium carbonate of the same
mass. Draw a line on the grid above to show how the volume of carbon dioxide
changes with time for this experiment.
(2)
4.2.3. At what time was the reaction just complete when small pieces of calcium
carbonate were used?
(1)
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1.7 Page 7 |
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Question 5
[9]
5.1 The table below shows the boiling points of some hydrogen compounds formed
by Group 6 elements:
H20
H2S
H2Se
HaTe
Boiling point/K | 373
212
232
271
State the strongest type of intermolecular force in water and in hydrogen
sulphide (H2S).
(2)
5.2
Draw a diagram to show how two molecules of water are attracted to each other
by the type of intermolecular force you stated in part (5.1). Include partial charges
and all lone pairs of electrons in your diagram.
(3)
5.3
Explain why the boiling point of water is much higher than the boiling point of
hydrogen sulphide.
(1)
5.4 When Ht ions react with H20 molecules, H30* ions are formed. Name the type
of bond formed when H* ions react with H20 molecules. Explain how this type of
bond is formed in the H30* ion.
(3)
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Question 6
[17]
Lewis (electron dot) structures are useful models.
6.1
Draw the Lewis (electron dot) structures of PF; and use the VSEPR theory to
deduce the molecular geometry including bond angles.
(3)
6.2
Predict whether the molecules PF3 and PFs are polar or non-polar.
(1)
6.3. ‘The table below gives the values of the first three ionisation energies of
magnesium:
First ionisation | Second ionisation | Third ionisation
energy
energy
energy
lonisation energy/kJmol? | 738
1451
7733
6.3.1 Write an equation to illustrate the process occurring when the first ionization
energy of magnesium is measured
(1)
6.3.2 Explain why the third ionisation energy of magnesium is very much larger than
the second ionisation energy of magnesium.
(2)
6.3.3 State and explain the trend in the first ionisation energy of the elements Mg to
Ba in Group Il.
(3)
6.3.4 There is a trend in the reactivity of the Group II metals with HzO. State the
conditions needed for Mg and Ca to react rapidly with H20. Write an equation for
each of these reactions.
(4)
6.3.5 Explain why Aluminium do not fit the expected trends of first ionisation energies
of period 3.
(3)
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Question 7
[9]
7.1
Draw a graph to show a Maxwell—Boltzmann distribution of molecular energies
for a gas. Label the axes. On the same axes draw a second curve to show the
distribution for the gas at a higher temperature. Label this second curve W.
(5)
7.2
A reaction of nitrogen monoxide is shown below:
2NO(g) + O2(g) > 2NO2(g)
The rate of reaction can be found by measuring the concentration of NO2 at
different times. Define the term rate of reaction. Draw a graph to show how the
concentration of NO2 changes with time. Indicate how the initial rate of reaction
could be obtained from your graph.
(4)
Question 8
[10]
8.1
Define the term standard enthalpy change of formation, AH%.
(1)
8.2
Define the term average bond enthalpy.
(1)
8.3
Consider the following equations:
3A + 6B > 3D AH = -403 kJ/mol
E + 2F > A AH =-105.2 kJ/mol
C>E+3D AH=+64.8 kJ/mol
Suppose the first equation is reversed and multiplied by 1/6, the second and third
equations are divided by 2, and the three adjusted equations are added. What is
the net reaction and what is the overall heat of this reaction?
(4)
8.4
Calculate AH for the reaction: C2Ha (g) + H2 (g) > C2He (g), from the following
data:
CaHg (g) + 302 (g) > 2CO2(g) + 2H20 (I) AH = -1411. kJ
CHzaHe(g) (g+)
+
%
3%
Oz
(Og2)
>(g)
>
H20
2
(IC)O2MH
(g=)
+ 3H20
-285.8
kJ(I)
AH
=
-1560.
kJ
(4)
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Question 9
[12]
91
Describe how aluminium is manufactured from purified bauxite. Illustrate your
answer by writing equations.
(5)
9.2
Reducing agents are used in the extraction of metals.
9.2.1 In terms of electrons, state the function of a reducing agent.
(1)
9.2.2 Identify a reducing agent used in the extraction of iron. Write an
equation for the redox reaction in which iron is formed from iron (III)
oxide using this reducing agent.
(2)
9.2.3. The iron formed in the blast furnace is impure. It contains about 5% of carbon and
other impurities, such as silicon and phosphorus. Describe how the percentage
of carbon is reduced and the other impurities are removed.
(4)
Question 10
[6]
Tin (Il) ions can be oxidised to tin (IV) ions by acidified potassium permanganate (VII)
solutions according to the following unbalanced equation:
Sn2*+ MnO*+ H* > Sn4*+ Mn?* H20
10.1 Identify the oxidising agent and the reducing agent from the equation above.
(2)
10.2 Balance the equation above.
(3)
10.3. Consider the following redox equation:
5 Fe* (aqyt MnO“a(ag)+ 8H*(aq)+ > SFe2* (ag)+ Mn?* (aq) + 4H20 1
Determine the oxidation numbers for Mn in the reactants.
THE END
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2 Pages 11-20 |
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