INSTRUMENTAL METHODS OF ANALYSIS
Oct/Nov.2003
Time:3 hours
THE KENYA NATIONAL EXAMINATIONS COUNCIL
DIPLOMA IN ANALYTICAL CHEMISTRY
INSTRUMENTAL METHODS OF ANALYSIS
3 Hours
INSTRUCTIONS TO CANDIDATES:
You should have the following for this examination:
Answer booklet
Scientific calculator.
This paper consists in sections; A and B.
Answer all the question s in section A and any THREE questions from section B
Each question in section A carries 4 marks while each question in section B carries 20 marks.
Maximum marks for each part of a question are as shown.

SECTION A (40 marks)
Answer all the questions in this section.
1. (a) Define the term “detection limit” of an analytical instrument.(1.5marks)
(b) The detection limit of an analytical instrument is quoted as 0.0005 absorbance.
Determine the transmittance of the instrument at this detection limit (2.5)marks

2. Three organic compounds X,Y and Z were analysed and the following observations made.
a) Both X and Y are 1.R active.
b) Both Y and Z are U.V active.
c) Z absorbs U.V radiation at a longer wavelength than Y.
State the conclusions that would be made from these observations.(4marks)
3. Describe how a G.L.C chromatography is prepared for analysis (4marks)
4. (a) Differentiate between “fuel- rich” and “fuel lean” flames as used in AAS. (3marks)
(b) State with reason which of the above flames is used for analysis of magnesium by ASS.(1 Mark)

5. List four causes of peak broadening in I.R spectra.(4marks)

6. (a) State two classical method of obtaining signals in flame photometry. (2marks)
(b) State how each of the above methods is used in both qualitative and quantitative analysis (2marks)

7. (a)List four types of motions executed by vibrating I.R .molecules.(2marks)
(b) A fundamental I.R absorption peak has a frequency µ =1051 cm-1 Calculate the frequency of first overtone.(2marks)
8. (a)State six disadvantages of flame methods of atomization over non flame methods (3marks)
(b)Explain why Zinc metal cannot be estimated by the method of flame emission spectroscopy. (1mark)
9. (a)Define the term “matrix” as used in Atomic absorption Spectrophotometry(ASS). (1mark)
(b) Give Two sources of background interference.(1mark)
(c) Explain why it is necessary to aspirate a blank in between samples during analysis by AAS.(2marks)
10. Discuss the role and importance of a nebulizer. (4marks) SECTION B (60 marks)
Answer any three questions from this section.
11. (a) (i)Draw a labelled schematic diagram of a double beam AA spectrophotometer. (16marks)
(ii) Describe how it works.
(b)State the advantages of a spectrophotometer over a photometer. (4marks)
12. An ore is suspected to contain ZINC .Describe the AAS analytical procedure for;
(a) Confirmation of presence of zinc in the ore. (9marks)
(b) Determination of concentration level of zinc in the ore.(11marks)
13. (a) (i)D efine the term “monochromator”.
(ii) Explain the necessity of monochromation in analysis. (5marks)
(b)With the aid of labelled sketches show the difference between diffraction an d dispersion types of monochromators. (10marks)
(c) With reference to the sample cell state with reason (s) the location of the monochromator in:
i. I.R. spectrophotometer
ii. U.V spectrophotometer.
(5marks)
14. (a) Describe the infrared base line method of determination of concentration of unknown sample. (14marks)
(b) The presence of an impurity X in propane was determined using absorption band of X at 2041cm-1 The data obtained is given below;

 

%X 1.00 2.00 3.00 4.00
Absorbance 0.240 0.481 0.719 0.915

(i)define the figure 2041 cm-1
(ii) calculate the percentage of X in an unknown sample that had an absorbance of 0.624 using the same cell and same instrument.(4marks)
15. (a) Explain why absorbance is often preferred to transmittance as an analytical parameter (illustrate your answer with sketches).
(8marks)
(b)30cm>3(3marks)
(C) substance X and Y have the retention time of 14.1 and 21.6 min, respectively , on a 24.7 cm column. The peak widths (at base) for X and Y are 4.16 and 4.72 min,
Respectively. Calculate:
(i) Column resolution.
(ii) Length of column necessary to separate X and Y with a resolution of 1.5.(9marks)



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