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APP601S - ANALYTICAL PRINCIPLES AND PRACTICE - 2ND OPP - JULY 2022 |
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o
NAMIBIA UNIVERSITY
OF SCIENCE AND TECHNOLOGY
FACULTY OF HEALTH, APPLIED SCIENCES AND NATURAL RESOURCES
DEPARTMENT OF NATURAL AND APPLIED SCIENCES
QUALIFICATION: BACHELOR OF SCIENCE
QUALIFICATION CODE: 07BOSC
LEVEL: 6
COURSE CODE: APP601S
COURSE NAME: ANALYTICAL PRINCIPLES AND
PRACTICE
SESSION: JULY 2022
DURATION: 3 HOURS
PAPER: THEORY
MARKS: 100
SUPPLEMENTARY/SECOND OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S) | DR JULIEN LUSILAO
MOpDERATOR: | DR MARIUS MUTORWA
INSTRUCTIONS
1. Answer ALL the questions in the answer book provided.
2. Write and number your answers clearly.
3. All written work MUST be done in blue or black ink.
PERMISSIBLE MATERIALS
Non-programmable calculators
ATTACHMENTS
List of useful tables, formulas and constants
THIS QUESTION PAPER CONSISTS OF 10 PAGES (Including this front page and attachments)
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Question 1: Multiple Choice Questions
[20]
1.1 A solution of which substance can best be used as both a titrant and its own
indicator in an oxidation—reduction titration?
(2)
(A) l2
(B) NaOCl
(C) K2Cr207
(D) KMnOg
1.2 A chemical or physical principle that can be used to study an analyte is called
(2)
(A) A technique
(B) A procedure
(C) A protocol
(D) A method
1.3 What is the number of O2 molecules in the 2.5 g of O2 inhaled by the average
person in one minute?
(2)
(A) 1.9 x 1022
(B) 3.8 x 1022
(C) 4.7 x 1074
(D) 9.4 x 102
1.4 How many millimoles of methane, CHa, are present in 6.4 g of this gas?
(2)
(A) 0.40
(B) 4.0
(C) 40
(D) 4.0 x 102
1.5 A1.50 mL sample of a sulphuric acid (H2SO.) solution from an automobile
storage battery is titrated with 1.47 M sodium hydroxide (NaOH) solution to a
phenolphthalein endpoint, requiring 23.70 mL. What is the molarity of the
sulphuric acid solution?
(2)
(A) 23.2 M
(B) 6.30 M
(C) 0.181 M
(D) 11.6 M
1.6 Consider this equation
__Sn?*(aq) +___MnO«¢-(aq) +___H*(aq) <> __Sn**(aq) + ___Mn?*(aq) + __H20(I)
When is balanced correctly, what is the ratio, Sn2*/MnOq?
(2)
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(A) 1/1
(B) 1/2
(C) 2/1
(D) 5/2
1.7 Sodium nitrate, heated in the presence of an excess of hydrogen, forms water
according to the two-step process
2NaNOQ3 — 2NaNOz2 + O2
2H2 + O02 — 2H20
From the reactions above, how many grams of sodium nitrate are required to form
9 grams of water?
(2)
(A) 21.3
(B) 42.5
(C) 69.0
(D) 85.0
1.8 What is the molarity of the sulphate ion in a solution prepared by dissolving 17.1 g
of aluminium sulphate, Al2(SO4)3, in enough water to prepare 1.00 L of solution?
Neglect any hydrolysis.
(2)
(A) 1.67 x 102 M
(B) 5.00 x 102M
(C) 1.50x 107M
(D) 2.50x 107M
1.9 For the reaction
PCl3(g) + Cl2(g) — PClIs(g), AH° = —86 KJ.
Under what temperatures is this reaction expected to be spontaneous?
(2)
(A) No temperatures
(B) Low temperatures only
(C) High temperature only
(D) All temperatures
1.10 Consider the ionization of hypochlorous acid: HOCI(aq) <> H*(aq) + OCF (aq)
has K = 3.0 x lO at 25°C.
What is K for the reaction: OCI-(aq) + H20(I) «+ HOCI(aq) + OH~(aq)?
(2)
(A) 3.0 x lo-®
(B) 3.0 x 10®
(C) 3.3 x 10”
(D) 3.3 x 107’
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Question 2
[15]
2.1 A group of scientists used radioactive isotopes to date sediments from lakes and
estuaries. To verify this method, they analysed a 2°8Po standard known to have an
activity of 77.5 decays/min and obtained the following results.
77.09
78.03
75.37
74.96
72.42
77.54
76.84
76.09
77.84
81.12
76.69
75.75
Determine whether there is a significant difference between the mean and the
expected value at a = 0.05.
(6)
2.2 Two analytical chemists have reported a method for monitoring the
concentration of SO2 in air. They compared their method to the standard
method by analysing urban air samples collected from a single location.
Samples were collected by drawing air through a collection solution for 6 min.
Shown here is a summary of their results with SO2 concentrations reported in
mL/m3.
standard
method:
new
method:
21.62
24.25
21.54
24.62
22.20
23.09
20.51
25.72
24.27
21.02
22.31
21.54
23.54
21.30
Using an appropriate statistical test determine whether there is any significant
difference between the standard method and the new method at a = 0.05.
(9)
Question 3
[20]
3.1 A standard sample contains 10.0 mg/L of analyte and 15.0 mg/L of internal
standard. Analysis of the sample gives signals for the analyte and internal standard
of 0.155 and 0.233 (arbitrary units), respectively. Sufficient internal standard is
added to a sample to make its concentration 15.0 mg/L. Analysis of the sample
yields signals for the analyte and internal standard of 0.274 and 0.198,
respectively. Report the analyte’s concentration in the sample.
(4)
3.2 Serum containing Na* gave a signal of 4.27 mV in an atomic emission analysis.
Then 5.00 mL of 2.08 M NaCl were added to 95.0 mL of serum. This spiked serum
gave a signal of 7.98 mV.
(a) What is the actual concentration of Na* spiked in the sample?
(2)
(b) Find the original concentration of Na* in the serum.
(3)
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(c) What calibration method has been used here?
(2)
(d) Briefly explain your choice of the calibration method.
(2)
(e) When would you recommend the use of this calibration method?
(2)
3.3 To analyse Mn7?* in water, the sample was placed in 50.00 ml volumetric flasks, each
containing 25.00 mL of the original sample and either of 0; 1.00; 2.00; 3.00; 4.00; or
5.00 mL of a 100.6 mg/L standard of Mn?*. All sample + standard solutions were
diluted to 50.00 mL before reading the absorbance. The equation for the obtained
calibration curve (shown in the figure below) is
Sspike = 0.0854 x Vstd oF 0.1478
0.60F
0.50 be
FE
0.40—
y-intercept = KACAVo.
Ve
Sspike 0.30 a
F
VE
0.20
0.10
a
Ob
hd
-2.00 \\
0
2.00
4.00
6.00
1
Vstd (mL)
x-intercept = ast
(a) Calculate the value for the x-intercept of the provided equation (beware the sign
and unit of the value).
(2)
(b) Calculate the concentration of Mn?*, C4 (beware the sign and unit).
(3)
Question 4
[15]
4.1 Given the following unbalanced redox reaction:
ClO-(aq) + | (aq) — 103 (aq) + Cl'(aq) Basic solution.
(a) Write the balanced oxidation and reduction half reactions as well as the overall
reaction.
(3)
(b) Calculate the state standard potential (£°) of the reaction
(E°cio./c. = + 0.890 V; E%03.).= + 0.257 V)
(1)
(c) Calculate the equilibrium constant (K) of the reaction.
(2)
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4.2 Calculate the ionic strength of a 0.050 M NaCl solution.
(2)
4.3 Calculate the pH of the following acid—base buffer: 5.00 g of NazCO3 and 5.00 g of
NaHCO3 diluted to 100 mL (Kz (HCO3") = 4.69 x 10°24),
(4)
4.4 Write the charge balance and mass balance equations for a 0.10 M NaCl solution.
(3)
Question 5
[30]
5.1 50.00 ml of 0.1 M NaCN is titrated with 0.1 M HNO3 (Ka for NaCN = 6.20 x 107°).
(a) Write the balanced reaction of the titration (only show the ions participating in
the reaction).
(1)
(b) Calculate the volume of HNO3 added at the equivalence point.
(2)
(c) Calculate the pH after addition of the following volumes of the titrant
(i) 0.0 mL of added HNO3
(4)
(ii) 25.0 mL
(4)
(iii) 50.0 mL
(4)
5.2 50.0 mL of 0.0250 M KI was titrated with 0.0500 M AgNOs3 (Ksp for Agl = 8.3 x 1072”).
(a) Write the reaction involved in the titration (i.e. only the ions participating to
the reaction).
(1)
(b) Calculate the value of equilibrium constant for the reaction in (a).
(2)
(c) Calculate the volume of titrant added at the equivalence point.
(1)
(d) Calculate pl for the following volume of added AgNO3
(i) 10.0 mL
(4)
(ii) 25.0 mL
(3)
(iii) 30.0 mL
(4)
TOTAL MARK = [100]
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Data Sheet
lealentated == F HW VN
tcaicutated = —vn
d
Ssaahd™ s?(N, —1)+s¢(—N1), tees
N, +M, E a sane — Nsets of data
y=
n
Confidence
dFergereedeosm 50%
90%
95%
99%
tealculated
xe = Xe]
= ————
pooled
~ AK
exp
1
1.000
6.314
12.706
63.656
2
0.816
2.920
4.303
9.925
3
0.765
2:353
3.182
5.841
4
0.741
2.132
2.776
4.604
5
0.727
2.015
2571
4.032
6
0.718
1.943
2.447
3.707
7
0.711
1.895
2.365
3.499
8
0.706
1.860
2.306
3.355
]
0.703
1.833
2.262
3.250
10
0.700
1.812
2.228
3.169
11
0.697
1.796
2.201
3.106
12
0.695
1.782
2.179
3.055
13
0.694
1.771
2.160
3.012
14
0.692
1.761
2.145
2.977
15
0.691
1.753
2.131
2.947
16
0.690
1.746
2.120
2.921
17
0.689
1.740
2.110
2.898
18
0.688
1.734
2.101
2.878
19
0.688
1.729
2.093
2.861
20
0.687
1.725
2.086
2.845
21
0.686
1.721
2.080
2.831
22
0.686
1.717
2.074
2.819
23
0.685
1.714
2.069
2.807
24
0.685
1.711
2.064
2.797
25
0.684
1.708
2.060
2.787
26
0.684
1.706
2.056
2.779
27
0.684
1.703
2.052
2.771
28
0.683
1.701
2.048
2.763
29
0.683
1.699
2.045
2.756
30
0.683
1.697
2.042
2.750
31
0.682
1.696
2.040
2.744
32
0.682
1.694
2.037
2.738
33
0.682
1.692
2.035
2.733
34
0.682
1.691
2.032
2.728
35
0.682
1.690
2.030
2.724
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Qerit (Reject if Qexp > Qerit)
N
90%
95%
99%
Confidence | Confidence | Confidence
3
0.941
0.970
0.994
4
0.765
0.829
0.926
5
0.642
0.710
0.821
6
0.560
0.625
0.740
7
0.507
0.568
0.680
8
0.468
0.526
0.634
9
0.437
0.493
0.598
10
0.412
0.466
0.568
N = number of observations
Soomp _
S othe
y, 4V, *Y, C.—Vv
OTVv. te at V.
Samp _
C,
Site
¥,
+
A
Vi+Vi,
Ved
sid
Vota
F(0.05, onum, odenom) for a Two-Tailed F-Test
onum> 1
2
3
4
5
odenl
1
647.8 799.5 864.2 899.6 921.8
2
38.51 39.00 39.17 39.25 39.30
3
17.44 16.04 15.44 15.10 1488
4
12.22 10.65 9.979 9.605 9.364
5
10.01 8.434 7.764 7.388 7.146
6
8.813 7.260 6.599 6.227 5.988
7
8.073 6.542 5.890 5.523 5.285
8
7.571 6.059 5.416 5.053 4.817
9
7.209 5.715 5.078 4.718 4.484
10
6.937 5.456 4.826 4.468 4.236
11
6.724 5.256 4.630 4.275 4.044
12
6.544 5.096 4.474 4.121 3.891
13
6.414 4.965 4.347 3.996 3.767
14
6.298 4.857 4.242 3.892 3.663
15
6.200 4.765 4.153 3.804 3.576
16
6.115 4.687 4.077 3.729 3.502
17
6.042 4619 4.011 3.665 3.438
18
5.978 4.560 3.954 3.608 3.382
19
5.922 4.508 3.903 3.559 3.333
20
5.871 4.461 3.859 3.515 3.289
co
5.024 3.689 3.116 2.786 2.567
6
937.1
39.33
14.73
9.197
6.978
5.820
5119
4.652
4.320
4.072
3.881
3.728
3.604
3.501
3.415
3.341
3.277
3.221
3.172
3.128
2.408
7
948.2
39.36
1462
9.074
6.853
5.695
4995
4529
4.197
3.950
3.759
3.607
3.483
3.380
3.293
3.219
3.156
3.100
3.051
3.007
2.288
8
956.7
39.37
1454
8.980
6.757
5.600
4.899
4.433
4.102
3.855
3.644
3.512
3.388
3.285
3.199
3.125
3.061
3.005
2.956
2.913
2.192
9
963.3
39.39
1447
8.905
6.681
5.523
4.823
4.357
4.026
3.779
3.588
3.436
3.312
3.209
3.123
3.049
2.985
2.929
2.880
2.837
2.114
10
968.6
39.40
1442
8.444
6.619
5.461
4.761
4.259
3.964
3.717
3.526
3.374
3.250
3.147
3.060
2.986
2.922
2.866
2.817
2.774
2.048
IS
984.9
39.43
14.25
8.657
6.428
5.269
4.568
4.101
3.769
3.522
3.330
3.177
3.053
2.949
2.862
2.788
2.723
2.667
2.617
2.573
1.833
20
993.1
39.45
14.17
8.560
6.329
5.168
4.467
3.999
3.667
3.419
3.226
3.073
2.948
2.844
2.756
2.681
2.616
2.559
2.509
2.464
1.708
co
1018
39.50
13.90
8.257
6.015
4.894
4.142
3.670
3.333
3.080
2.883
2.725
2.596
2.487
2.395
2.316
2.247
2.187
2.133
2.085
1.000
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Physical Constants
Gas constant
R
= 8.315) K+ molt
= 8.315 kPa dm? K* mol?
= 8.315 Pa m? K+ molt
= 8.206 x 10% L atm K+ mol
Boltzmann constant
k
= 1.381 x 103 J K?
Planck constant
h
= 6.626 x 1074) K+
Faraday constant
F
= 9.649 x 10*C mol?
Avogadro constant
Lor Na
= 6.022 x 107 mol™
Speed of light in vacuum
c
= 2.998 x 108 ms?
Mole volume of an ideal gas
Vin
= 22.41 L mol (at 1 atm and 273.15 K)
= 22.71 L mol™ (at 1 bar and 273.15 K)
Elementary charge
e
= 1.602x 10°C
Rest mass of electron
Me
= 9.109 x 10°+kg
Rest mass of proton
Mp
=1.673x102’kg
Rest mass of neutron
Mn
= 1.675 x 10°’ kg
Permitivity of vacuum
So
= 8.854 x 10° C* J4m? (or Fm?)
Gravitational acceleration
g
= 9.807 ms?
Conversion Factors
1W
=1Js?
1J
= 0.2390 cal=1Nm=1VC
= 1Pam?=1kgm?s?
1 cal
= 4,184J
1eV
= 1.602 x 10°°J
1Latm
= 101.3 J
1 atm
= 1.013 x 10° N m? = 1.013 x 10° Pa =
760 mmHg
1 bar
=1x10°Pa
1L
= 107=m1 ?dm?
1 Angstrom
=1x107m=0.1 nm =100 pm
1 micron (1)
=10®m=1um
1 Poise
=0.1 Pas=0.1N sm?
1 ppm
=1pgg?=1mgkg?
= 1 mg L? (dilute aqueous solutions only)
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