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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