LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2006

                                                 CH 3805 – ANALYTICAL CHEMISTRY – III

 

 

Date & Time : 18-04-2006/AFTERNOON   Dept. No.                                                       Max. : 100 Marks

Part–A (20 Marks)

Answer ALL questions (10 x 2 = 20)

1. How large a sample to be taken for analysis using a chemical balance so that the maximum relative uncertainty in the sample weight is 5 ppm?
2. Explain replacement titration with an example.
3. Compute the equivalent point potential for titration of
   A²⁺ vs B⁴⁺ (SRP: B⁴⁺ / B²⁺ = 1.44 V ;  A⁴⁺ / A²⁺ = 0.15V )
4. How is an indicator chosen for a red ox titration?
5.  Calculate the equilibrium constant for the following reaction:

HCN + OH^–   ⇌  CN^– + H₂O; K_a (HCN) = 1 x 10 ^-10

1. How does coulometer differ from potentiometric technique?
2. Explain how the addition of nitrate ion avoids the liberation of hydrogen?
3. State an expression for the residual current and explain the terms in it.
4. Explain the effect of added CN^–  on the electrode deposition of Ag.
5. Mention any two applications of DTA.

 

Part–B (40 Marks)

 

Answer any EIGHT questions (8 x 5 = 40)

1. Show that the equivalence point for the titration of Fe²⁺ vs MnO₄^– is pH dependant.
2. Explain diverse ion effect
3. Draw  the titration curves for the follwing:

• 20 mL of 0.1 M NaOH vs 0.1M CH₃COOH
• 20 mL of 0.1 M NaOH vs 0.1M H₂SO₄.

1. Write a note on homogeneous precipitation.
2. Exactly 0.3525 g of 96.5% Na₂SO₄ required 37.7 mL of a solution of BaCl₂. Calculate the concentration and express the concentration of BaCl₂ in scientific notation.
3. The values of Ka₁, Ka₂, Ka₃ & Ka₄ for EDTA (H₄Y) are 1x 10^-2 , 1x 10^-3 , 1x 10^-8  & 1x 10^-12 ,  respectively. Calculate the conditional stability constant for the following process in 1x 10^-2 M HCl.

Fe³⁺ + Y^4-     ⇌       FeY^–     ; K_obs = 1 x 10²⁵

1. 1. How will you estimate Cu²⁺ by electro gravimetric method?

 

1. Draw a typical polarogram and indicate the following on the diagram.

1. Residual current.
2. Limiting current
3. Diffusion current
4. How are they related to each other?

1. A certain Pb²⁺ solution gives i_d = 1.00 mA . To 10 ml of the solution 0.5 ml of 0.04 M of Pb²⁺ was added. The i_d of the solution was found to be 1.5 mA. Calculate the concentration of Pb²⁺ in the unknown solution.
2. Draw and explain the ampereometric titration curves for the following titrations if the applied potential is maintained at half wave potential of Pb²⁺

1. Pb²⁺ vs CrO₄^2- b . CrO₄^2- vs Pb²⁺

1. Explain how the cyclic voltometric technique can be used to determine the electrochemical reversibility and stability of a red-ox  system.
2. Explain the following with an example.

(i) Fluorimetric estimation of metal ions

(ii) Chemiluminescence

 

Part-C (40 Marks)

 

Answer any FOUR questions (4 x 10 = 40)

1. The following are peak areas for chromatogram of standard solutions of methyl vinyl ketone (MVK)

Conc. MVK mmol-1	Relative peak Area
0.500	3.76
1.50	9.16
2.50	15.03
3.50	20.42
4.50	25.33
5.50	31.97

Apply method of last squares to determine the Conc. of MVK in a sample which yielded relative peak area 6.3, which is the mean of 4 measurements. Also calculate the standard deviation of the result.

1. Give a critical account of acid-base titration in non-aqueous solvents.
2. a) Determine the concentration of Fe²⁺, Fe³⁺, Ce⁴⁺ and Ce³⁺ in the mixture containing 20.00mL of 0.1000M Ce⁴⁺ and 40.00ml of 0.0500M Ce²⁺ in acidic medium.

(Eº _Fe³⁺_/Fe²⁺ = 0.8V, Eº_Ce⁴⁺_{/ Ce}³⁺ =1.4V)

1. b) Discuss the factors which influence ∆P^m at the equivalence point.

1. a) Explain the components of spectro flurometer with a neat diagram.

1. b) What is hollow cathode? How does it work?

1. a) Bring out the difference between TG and DTA.

1. b) How will you prove the liberation of CO in a thermal analysis?

1. A metal carbonate, MCO₃.4H₂O (at.wt of metal = 74) on thermal analysis becomes  dihydrate at  160˚C , monohydrate at 200˚C , anhydrous at 260˚C and MO at 550˚C Construct a TG, using graph sheet if 0.725 mg of the salt hydrate is heated from 40˚C to 750˚C.

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                           LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

AD 21

THIRD SEMESTER – NOV 2006

CH 3805 – ANALYTICAL CHEMISTRY – III

 

 

Date & Time : 08-11-2006/9.00-12.00   Dept. No.                                                   Max. : 100 Marks

 

 

 

PART – A

Answer ALL the questions                                                                            ( 10 x 2 = 20 marks)

 

1. How many litres of water can be chlorinated using 1 kg bleaching powder containing 30% available chlorine.  Assume the allowable limit of cl₂ in water is 2 ppm.
2. Can ‘trien’ be used as a titrant to estimate Cu⁺²? Why?
3. How are indicators chosen for redox titration?
4. Compare the solubility of lead iodide in (i) pure H₂O  (ii) 0.1 M aq. KNO₃
   (iii) 0.1 M aq. KI.
5. Define confidence interval.
6. How does potentiometry differ from voltametry.
7. Differentiate electrogravimetry and coulometry.
8. Draw the plot of Emf vs Time for

• Linear sean
• Differential pulse.

1. What is supporting electrolyte?  Explain its role.
2. Define quantum yield.  Account for the high quantum yield of the reaction between H₂ and Cl₂.

 

PART – B

 

Answer any EIGHT questions                                                                       (8 x 5 = 40 marks)

 

1. How will you proceed to collect authentic data from research?
2. Explain the importance of vonweimarnn ratio in gravimetric analysis.
3. Discuss the factors which influence Dpm/Dv in complexometry.
4. describe the salient features of acid base titration in non-aqueous solvents?
5. Show that the equivalence point potential for the titration of Fe⁺² vs MnO in acidic medium is dependent on pH.
6. Draw the titration curve for the titration of 20.00mL of 0.1000 m CH₃COOH vs
   0.0500 m NaOH.  K_a of CH₃COOH is 10^-5.
7. a) How will you determine electrode discharge potential.

1. b) Explain the factors that may affect the nature of electro deposition.

1. Draw a typical cyclic voltagram and indicate i_p(a) , i_p(c), E_p(a) and E_p(c) on the diagram.
2. Explain how polarographic method can be used in quantitative studies.
3. Explain the following briefly
   a) Flame photometry      b) Atomic absorption spectroscopy.
4. Explain the construction and working of hallocathode.
5. How will you prove the liberation of carbon monoxide.  Illustrate with an example.

 

 

 

 

PART – C

 

Answer any FOUR questions                                                                   (4 x 10 = 40 marks)

 

1. Cone common way 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 of
   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.	Absorbance at 650 nm
1.00	0.230
2.00	0.436
3.00	0.638
4.00	0.848
Urine sample	0.518

Apply the method of least squares to fine the slope, intercept and the standard deviation

of the results Determine the concentration of  P in ppm in Urine sample.

 

1. 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 filtrated 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 tholulfate;  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 a 100.00 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 Sn by difference.

 

1. a) Find out the gravimetric factor if Fe⁺³ is precipitated as Fe(OH)₃ and weighed asFe₂O₃.

1. b) A 0.6407 g sample containing Cl^– and I^– gave silver halide precipitate weighing
   4430 g. This precipitate was than strongly heated in a stream of Cl₂ gas to convert the AgI to Agcl; On completion of this treatment, the precipitate weighted 0.3181 g. Calculate the percentage of Cl^– and I^– in the sample.

 

1. a) Draw a typical polarogram and indicate (i) residual current (ii) limiting current
   (iii)diffusion current on the graph drawing.

1. b) State Ilkovic equation. Explain the terms in it and its applications.

 

1. a) Explain how cyclic voltametry is usefull to determine (i) reversibility
   (ii) Electro chemical stability of a reaction.

1. b) Write a note on chemiluminescence.

1. a) Explain a and differentiate the following  (i) TGA & DTGA  (ii) DSC & DTA

1. b) Calcium oxalate mono hydrate loses H₂O at 100 – 250^o Co (at 400 – 500^oC) and

CO₂ (at 650 – 660^o C) Draw its TGA when 0.25 g is heated to 700^oC at fixed

Atmosphere.

 

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