Gujarat University 2005 B.Sc Chemistry -X - Question Paper

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(b) How a monochromatic light is found by a prism and a grating ? discuss how a mixture of 2 substances can be determined simultaneously by a spectrophotometer. If the cell is not exactly perpendicular to the beam but falls at an angle of 85° what fault will outcome ?
(c) What is the necessity of a hollow cathode lamp ? discuss its working. discuss the methods used for background correction in atomic absorption spectroscopy. Why non-metals are not determined by AAS ?
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TB-04 6
(c) (i) explain the importance of ion exchange equilibria in ion-exchange chromatography. define factors that affect the selectivity of ion exchange resins.
(ii) Write a note on photometric fault.
4. (a) ans any 2 of the subsequent : (14)
(i) explain the effect of CO2 introduced during an acid-base titration, either from the atmosphere or from the titrating solutions. How this fault may be eliminated ?
(ii) By differential titration of alkalies, how will you know whether a provided sample of alkali contains :
(1) Sodium bicarbonate and sodium carbonate?
(2) Only sodium carbonate?
(3) Sodium hydroxide and sodium carbonate?
(iii) discuss the titration of Na2CO3 against HCl.
(iv) Construct a curve for the titration of 25 ml. of 0.1 M maleic acid, C2H2(COOH)2 with 0.1 M NaOH. K1 and K2 of maleic acid are respectively 1.2 × 10–2 and 5.96 × 10–7.
(b) ans any 2 of the subsequent :
(i) define 3 general methods for performing EDTA titrations. elaborate the advantages of every ?
(ii) Why a small amount of MgY-- often added to a solution that is to be titrated for hardness ?
(iii) Derive a curve for the titration of 50 ml. of 0.005 M Ca++ with 0.01 M EDTA in a solution buffered to pH 10. compute pCa values on addition of 10 ml EDTA and at the equivalence point. a4 at pH 10 is 0.35. The stability constant of CaY is 5.0 × 1010.
(iv) explain giving suitable examples the effect of masking, demasking and control of pH on the selectivity of EDTA titrations.
TB-04 7
5. ans any 3 of the subsequent : (14)
(a) Prove that a tenfold increase in the reagent concentration will increase the extraction efficiency by identical amount as an increase in the pH of 1 unit.
(b) What is peptization ? How is it avoided ?
describe : Digestion, Counter-ion layer, Relative supersaturation.
(c) In Mohr titration of Cl– against AgNO3, compute the concentration of indicator, K2CrO4, needed. The solubility products of AgCl and Ag2CrO4 are 1.2 × 10–10 and 1.7 × 10–12 respectively. Why Mohr titration is performed in neutral or slightly alkaline solution? Why I– cannot be titrated by Mohr method ?
(d) explain the advantages and disadvantages of 3 adsorption indicators.
(e) What is Von Wiemarn ratio ? describe the terms involved. What info concerning the optimum conditions for precipitation does it provide ?
(f) discuss : Accuracy and Precision; fault and Deviation; Mean and Median.
discuss standard deviation. What is meant by determinate fault and indeterminate fault ?
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TB-04 8

Earning:   Approval pending.