LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

DB 24

M.Sc. DEGREE EXAMINATION – CHEMISTRY

FIRST SEMESTER – November 2008

    CH 1809 – ANALYTICAL CHEMISTRY

 

 

 

Date : 11-11-08                 Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

PART A

Answer all the questions.                                                                                  10 x 2 = 20

1. Lead was determined in a sample of dust and the following results were obtained

4.3, 4.1, 4.0 and 3.2 µg /g. Should the last value 3.2 µg /g be rejected? The critical value of Q for four measurements is 0.831.

2. What are gross errors?
3. Define intersystem crossing.
4. Mention any four compounds used to derivatise the samples for GC.
5. A random sample of 9 observations shows a mean of 4.13 with a standard deviation of 0.189. Test whether the sample values deviate from the mean of 4.0. (t_95% = 2.306)
6. How much of NaF must be added in 1000 liters of water so that the concentration of F^– is equal to 1 ppm?
7. What is a masking agent? Give an example.
8. Differentiate coulometry from voltammetry.
9. Write Ilknoic equation and mention the terms involved.
10. Calculate the pH at the equivalence point when 20 ml of 0.1M NH₄OH is treated with 0.2M HCl _(aq) . K_b of NH₄OH is 1.8 x 10 ^-5.

PART B

Answer any eight questions.                                                                                8 x 5 = 40

11. What are determinate errors? Explain any four types of determinate errors.
12. On heating NaHCO₃ (Mol. weight is 84) it decomposes between 100 – 225°C with the loss of H₂O and CO₂. The total weight loss due to H₂O and CO₂ is 35.8 percent by weight, whereas the weight loss due to CO₂ alone is 25.4%. Calculate the millimoles of NaHCO₃ decomposed and deduce the stoichiometry of the reaction.
13. What are the different types of columns used in GC? Explain.
14. The normality of a solution is determined by four separate titrations, the results being 0.2041, 0.2049, 0.2039 and 0.2043. Calculate the mean, median, average deviation, standard deviation and coefficient of variation.
15. Discuss the types of burners used in AAS and mention any one advantage for each.
16. How is codeine and morphine in a mixture determined by fluorimetry?
17. Explain the salient features of non-aqueous acid-base titrations with a specific example.
18. Calculate the molar solubility of BaSO₄ in 0.01M NaNO₃ solution (the thermodynamic solubility product of BaSO₄ at 25°C is 10 ^-10.
19. 50 ml of 0.0.1M Ca ²⁺ is titrated with 0.01M EDTA at pH= 10. K_abs for CaY^2- is 5 x 10 ¹⁰ and a₄ at pH 10 is 0.35. Calculate p_ca after adding 60 ml of the titrant.
20. Derive an expression for equivalence point potential for the redox reaction between Cr₂O₇ ^2- and Fe²⁺ in acid medium to form Cr³⁺ and Fe³⁺.
21. Explain the working of a biochemical ion selective electrode with an example.
22. Discuss the theory of adsorption indicators in precipitation titrations.

 

PART C

Answer any four questions.                                                                              4 x 10 = 40

23. What are spectrophotometric titrations? How are they carried out? Explain the different types of spectrophotometric titrations with examples.
24. a) Explain the factors affecting the fluorescence emission.
25. b) Write short notes on the chemical interferences in flame emission spectroscopy.                                                                                                    (5+5)
26. a) Draw and explain the working principle of flame ionization detector.
27. b) Explain briefly the instrumentation in turbidimetry.                                     (5+5)
28. Calculate the relative error when 50 ml of 0.1M Cl^– is titrated with 0.1M AgNO₃. The initial concentration of K₂CrO₄ (indicator) is 2 x 10 ^-3M. Assume that the titration is stopped at the very onset of Ag₂CrO₄ precipitate formation. K_sp of AgCl and Ag₂CrO₄ are 1.8 x 10 ^-10 and 1.2 x 10 ^-12 respectively.
29. Explain any two of the following:
30. a) Principle and applications of stripping voltammetry
31. b) colulometric titration
32. c) Feasibility of acid-base titrations
33. d) Metallochrome indicators. (5+5)
34. 0.7362g of sample containing only Ca(NO₃)₂.4H₂O, NaCl and KCl is dissolved in water and diluted to 100 ml. (solution X). A 25 ml portion of X is titrated with 25 ml of 0.01M EDTA. Another 25 ml portion of X is treated with 25 ml of 0.1M AgNO₃ and excess of Ag⁺ is back titrated with 4 ml of 0.1250M KSCN solution. Calculate the percentage of each in the sample.

 

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