LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

«degree» DEGREE EXAMINATION – CHEMISTRY

«semester» SEMESTER – APRIL 2007

CH 3805-   CHEMISTRY

 

 

 

Date & Time: «date» / «time»      Dept. No.                                       Max. : 100 Marks

 

 

PART – A

Answer ALL the questions.                                        (10 ´ 2 = 20 marks)

 

1. Define confidence interval.
2. 200 g sample of a well water is found to contain 0.1132 g calcium oxide. Determine the concentration of calcium in well water in ppm.
3. What is the gravimetric factor for Fe⁺³, when it is precipitated as ferric hydroxide and weighed as ferric oxide.
4. Explain ‘replacement titration’ with an example.
5. Predict the equivalence point potential for the system: B⁺  vs  A⁺⁴

 

A⁺⁴ + 2e^–  ⇌  A⁺

 

B⁺⁴ + 3e^–    ⇌  B⁺

 

6. Distinguish coulometry and voltametry.
7. What is residual current? What is it due to?
8. Mention two applications of DTA.
9. Explain the effect of pH on electrode deposition.
10. How is K⁺ ion in serum determined?

 

PART – B

Answer any EIGHT questions.                                   (8 ´ 5 = 40 marks)

 

11. Show that equivalence point potential is pH dependent for the titration of Fe⁺² vs MnO₄^–  in acidic medium.
12. What is diverse ion effect? How is it explained?
13. Prove that the conditional formation constant in EDTA titrations is pH dependent.
14. Discuss the salient features of acid base titration in non-aqueous solvents.
15. Describe the factors which influence Dpm/DV in complexometry.
16. Draw the titration curve for the titration of 20.00mL of 0.1000 M CH₃COOH  vs  0500 M NaOH K_a of CH₃COOH is 10^-5.
17. Draw a typical cyclic voltagram and indicate I_p(a), I_p(c),  E_p(a) and E_p(c) on the diagram.
18. Explain how polarographic method can be used in quantitative studies.
19. Briefly explain:

(i)  Flame photometry             (ii) Atomic absorption spectroscopy

20. Write notes on neutron activation analysis.
21. How is Fe⁺³ determined by spectrophotocolorimetric method?
22. 00 g of p-nitroaniline in 100 mL of 0.1 N HCl solution shows an absobance of 0.825 at its l_max when measured in a cell with 1.0 cm thickness. An unknown sample of the same compound in the 0.1 N HCl solution in the same cell shows an absorbance of 0.500. Calculate the amount of p-nitroaniline in solution in g/Litre.

 

 

 

 

 

 

 

 

 

 

PART – C

Answer any FOUR questions.                                                (4 ´ 10 = 40 marks)

 

23. A common method to determine phosphorus in urine is to treat the sample after removing the protein, with molybdenum(VI) and then reduce the resulting 12-Molybdophosphate complex with ascorbic acid to give an intense blue coloured species called Molybdenum blue.  The absorbance of Molybdenum blue can be measured at 650 nm.  A patient produced 1122 mL of urine in 24 hours.  A 1.00 mL aliquot of the sample was treated with Mo(VI) and ascorbic acid and was diluted to a volume 50.00 mL.  A calibration curve was prepared by treating 1.00 mL aliquots of phosphate standard solutions in the same manner as the urine sample.  The absorbances of the standards and the urine sample were obtained at 650 nm and the following results were obtained

Solution ppm of P	Absornace at 650 nm
1.00 2.00 3.00 4.00 Urine sample	0.230 0.436 0.638 0.848 0.518

Apply the method of least squares to find the slope, intercept and the standard deviation of the result.  Determine the concentration of P in ppm in the urine sample.

24. 4800 g sample that contains KCl and KI gave a precipitate of 0.2720 g silver halide. A 0.7200 g sample of the same material is titrated with    0.1020 M AgNO₃ requiring 25.80 mL.  Calculate the percentage of KCl and KI in the sample.
25. Discuss the principle and instrumentation of TGA.
26. (a) Draw a neat polarogram and explain the features.

(b) Write a note on chemiluminescence.

27. Differentiate the following:

(a) Phosphorescence and fluorescence

(b) TGA and DTA

28. A 0.3284 g sample of brass (containing Pb, Zn, Cu, Sn) was dissolved in HNO₃. The sparingly soluble SnO₂.4H₂O was removed by filtration and the combined filtrate and washings were then diluted to 500.00 mL.  A 10.00 mL aliquot was suitably buffered; titration of the Pb, Zn, Cu in this aliquot required 37.56 mL of 0.002500 M EDTA.  The copper in a 25.00 mL aliquot was masked with thiosulphate; the Pb and Zn were then titrated with 27.60 mL of the EDTA solution.  Cyanide ion was used to mask the Cu and Zn in  00 mL aliquot; 10.80 mL of the EDTA solution was needed to titrate the Pb ion.   Determine the composition of the brass sample; Evaluate the percentage of tin by difference.

 

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