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Chem 308: Analytical Chemistry I Question Paper
Chem 308: Analytical Chemistry I
Course:Bachelor Of Environmental Science
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
THIRD YEAR EXAMINATION FOR THE AWARD OF DEGREE OF
BACHELOR OF SCIENCE (ENVIRONMENTAL SCIENCE)
CHEM 308: ANALYTICAL CHEMISTRY I
STREAMS: B.SC (ENSC) TIME: 2 HOURS
DAY/DATE: MONDAY 12/8/2013 11.30 A.M. – 1.30 P.M.
INSTRUCTIONS:
Answer Question ONE and any other TWO Questions.
Useful Data:
R = 8.3143V deg-1mol-1 K-1
0oC = 273.16 K
1 Faraday (F) = 96,487 Coul.equiv-1
Lnx = 2.303 log x
QUESTION ONE (30 MARKS)
(a) (i) What tasks relating to the chemical analysis of a material sample must be
performed prior to beginning the actual laboratory work? [ ½ mark]
(ii) If a water sample is to be analyzed for trace levels of metals, why is a glass container for sampling and storage inappropriate? [ ½ mark]
(iii) Explain why the quality of all reagents used in the laboratory be assured before use. [ ½ mark]
(b) (i) Given the care with which laboratory equipment (balances, burets,
instruments, etc) are calibrated at the factory, why should the chemical analyst worry about errors? [1 ½ marks]
(ii) An analyst determines that the analytical balance he/she used in a given analytical test is wrongly calibrated. Is there an indeterminate error? Explain. [1 ½ marks]
(iii) A given analytical test was performed five times. The results to the analysis are represented by the following values: 6.738, 6.738, 6.737,
6.739, 6.738. Would you say that these results are precise? Can you say that they are accurate? Explain your answers. [1 mark]
(c) (i) What role does vapor pressure play in a GC separation? [1 mark]
(ii) There are three heated zones in a GC instrument. Which zones are these and why does each need to be heated? [1 ½ marks]
(iii) Explain the principles by which qualitative analysis can be performed in GC with the use of retention time. [2 marks]
(d) (i) Why is the HPLC an improvement over the “open column” technique?
[1 mark]
(ii) Why must mobile phases and all samples and standards be finely filtered before an HPLC experiment? [ ½ mark]
(iii) Why must HPLC mobile phases and samples be degassed prior to use in the HPLC system? [1 mark]
(e) (i) Why is platinum electrode needed in some half cells. [1 mark]
(ii) What is the “supporting electrolyte” and why does it not interfere with the
measurement of the analyte in a polarography experiment? [1 ½ marks]
(iii) Explain the reference to half wave potential as an electrochemical barrier.
[1 ½ marks]
(f) (i) Why must a premix burner have a drain line attached? What safety hazard
exists because of this drain line and how do we deal with it? [1 ½ mark]
(ii) Why is the colour of a flame containing sodium atoms different from that of a flame containing potassium atoms? [2 marks]
(iii) There is no monochromator placed between the light source and the flame in an AA experiment. Why is this? [3 marks]
(iv) Explain with the help of a diagram the mechanism of the excitation process in the hollow cathode lamp. [7 marks]
QUESTION TWO (20 MARKS)
(a) A new gravimetric method is developed for iron (III) in which the iron is
precipitated in crystalline from with an organoboron “cage” compound. The accuracy of the method is checked by analyzing the iron in an ore sample and comparing with the results using the standard precipitation with ammonia and weighing of Fe2 O3. The results reported as % Fe for each analysis were as follows:
Test method Reference method
20.10% 18.89%
20.50 19.20
18.65 19.00
19.25 19.70
19.40 19.40
19.99
Is there a significant difference between the two methods? [6 marks]
(b) The following replicate calcium determinations on a blood sample using atomic absorption spectrophotometry (AAS) and a new colorimetric method were reported. Is there a significant difference in the precision of the two methods?
AAS
mg/dl
10.9
10.1
10.6
11.2
9.7
10.0
-
-
Colorimetric
mg/dl
9.2
10.5
9.7
11.5
11.6
9.3
10.0
11.2
[6 marks]
(c) From the following data, determine the linear least squares line and calculate the phosphorous concentration in the urine sample.
PPm of P
1.00
2.00
3.00
4.00
Urine sample
A
0.205
0.410
0.615
0.820
0.625
[8 marks]
QUESTION THREE (20 MARKS)
(a) Write the Van Deemter equation and identify all symbols in it. [3 marks]
(b) Seven identical portions of a substance were chromatographed on the same column at different flow velocities and the results obtained are given in the
table below.
Sample Flow velocity
in Cms-1 Retention
time
(S) Peak width
at half-heights
1 7.0 625 7.9
2 10.0 438 5.2
3 15.0 292 3.2
4 25.0 175 1.9
5 40.0 110 1.2
6 60.0 73 0.8
7 80.0 61 0.7
Draw a Van Deemter plot. [15 marks]
Determine the optimum flow velocity. [ ½ mark]
Calculate the theoretical plates at the optimum flow velocity.
[1 ½ marks]
QUESTION FOUR (20 MARKS)
(a) Explain the difference between instrument optimization and instrument
calibration. [2 marks]
(b) Outline the basic principles of the internal standard method of calibrating analytical instruments. [3 ½ marks]
(c) Sodium and potassium in blood serum are commonly determined by the flame emission technique using Lithium as an internal standard. Standard solutions were prepared using various amounts of Na+ and K+ with a fixed amount of Li+
all diluted to 25.0 cm3. A 10 cm3 serum sample was similarly treated and the following data were obtained.
Sample Volume in cm3
of 8g/L of Na+ Volume in cm3
of 0.45g/L of K+ Volume in cm3
of 5.0g/L of Li+ Emission
signal
standard added standard added standard added Na+ K+ Li+
1 1.00 1.00 5.00 51 3.2 64.0
2 3.00 3.00 5.00 165 11.0 69.0
3 5.00 5.00 5.00 247 16.1 62.2
4 7.00 7.00 5.00 340 20.9 61.1
5 9.00 9.00 5.00 481 30.0 60.8
Unknown - - 5.00 275 18.0 67.9
Prepare a calibration plot for sodium. [9 marks]
Determine the amount of Na+ in the serum. [ ½ mark]
(d) (i) State three properties of ion selective membranes which lead to their sensitivity
and selectivity toward certain cations. [1 ½ marks]
What is the new cell potential (E) for the Cu2+/Cu//Ag+1/Ag cell? If
[Cu2F] = 0.1M and [Ag+1] = 10-2 M at 25o C given that
Cu + 2Ag+1? Cu+2 + 2Ag Eo = + 0.46V
[R = 8.3143V Coul. Deg-1 mol-1, 0oC = 273.16K],
F[Faraday constant) = 96,487 Coul. Equiv-1) ln = 2.303 log.y [2 marks]
Calculate the pH of a solution whose potential at 25oC measured with hydrogen electrode at an atmospheric pressure of 1.012 atm (corrected for the vapour pressure of water at 25oC) is -0.324V. {R = 8.3143V Coul.deg-1 mol-1,
0oC = 273.16K, F(Faraday constant) = 96.487 Coul. equiv-1), ln = 2.303 log}.
[2 ½ marks]
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