LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 45

FOURTH SEMESTER – APRIL 2008

CH 4808 – ELECTROCHEMISTRY

 

 

 

Date : 21-04-08                  Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

PART A

Answer ALL questions                                                                (10 x 2 = 20 Marks)

 

1. Calculate the thickness of the ionic atmosphere in 0.10M aqueous solution of

barium chloride at 298K. (Dielectric constant of H₂O at 298K = 78.6).

2. Derive the expression for the rate of an electrode reaction using Faraday’s law.
3. An electrolyte of the type A₂B₃ is 85% ionized in 0.01M solution.

What is the value of Vant’ Hoff  i factor?

4. What is Wien effect?
5. Write Lipmann equation and explain the terms.
6. What are the factors which affect the symmetry factor in an electrode reaction?
7. Explain the various factors which influence the zeta potential.
8. What is meant by stoichiometric number?
9. Removal of oxygen from analyte is very essential in polarographic analysis.Why?
10. Write the expression for the charge transfer resistance in an electrode reaction

at low overpotential.

 

PART B

 

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

 

11. Discuss the Born model for ion- solvent interactions.
12. Account for the abnormal conductance of H₃O⁺ ion in protic solvents.
13. Explain the electrokinetic phenomena on the basis of irreversible thermodynamics.
14. Calculate the values of Debye Huckel Onsager constants A and B for methanol

at 298K. (For methanol  ε =31.5 and  η = 0.545 centipoise).

15. Distinguish between polarisable and non-polarisable electrodes with

suitable examples.

16. Discuss the mechanism of electro-reduction of nitrobenzene.
17. Explain how electrophoretic and relaxation effects affect the mobility of

an ion in solution.

18. What are the advantages of DME? Mention two of its disadvantages.
19. What is zeta potential? How is it determined?
20. Deduce Nernst equation from Butler – Volmer equation.
21. Explain: Half-wave potential and Residual current
22. Calculate the mean ionic activity co-efficient in 0.01M aqueous solution of

potassium ferrocyanide at 298K using Debye – Huckel limiting law.

 

 

 

 

 

 

PART C

 

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

 

23. Derive Debye Huckel Onsager equation. How is it verified?

What are its limitations?

24. Discuss the Stern model of double layer structure.

How is it superior to other models?

25     a).Derive Butler – Volmer equation for a single step one electron transfer reaction.

1. b) Discuss the high field and low field approximations of the above equation.
2. a)Describe any two applications of polarography.

b)Calculate the maximum diffusion current in the polarographic reduction of Zn⁺²

ions from a 3 x 10^-3 M solution with diffusion co-efficient of 7.2 x 10^-6 cm² s^-1.

The capillary used in DME is such that it liberates 1.5 mg of Hg per second

with a drop time of 2 seconds.

27. Discuss the use of Pourbaix diagram in understanding the thermodynamic stability

of iron at different pH values.

28     a).A 0.2m solution of lead nitrate freezes at -0.10^o C If K_f  of water is 1.86 Kmolal^-1

          what is the degree of dissociation of lead nitrate in 0.20m solution?

b)Consider the following  mechanism for the reduction of I₃ ^–   ion

 

Step 1                 I₃^–       I₂    +    I^–

^–

Step 2                 I_{2     ­}    2 I

 

Step 3                 2 (I  +  e^–     →    I^– )

 

 

Derive the rate equation for the reaction considering step 3 as the rate determining

step and explain how the electrochemical- reaction orders establish the mechanism.

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

GH 59

M.Sc. DEGREE EXAMINATION – CHEMISTRY

FOURTH SEMESTER – APRIL 2008

    CH 4805 / 1020 – ELECTROCHEMISTRY

 

 

 

Date : 03/05/2008            Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

PART A

Answer ALL questions                                                                      (10 ´ 2 = 20 Marks)

 

1. Calculate the ionic strength in 0.01M potassium ferricyanide solution.
2. Explain the significance of symmetry factor in an electrode reaction.
3. How does electrophoretic effect affects the ionic mobility in a solution of strong electrolyte?
4. Explain IHP and OHP at the electrode – electrolyte interface.
5. What is meant by Lippmann potential?
6. Explain concentration polarization.
7. Vant Hoff ‘ i ‘ factor for AB₂ type electrolyte at a given concentration is 2.8. What is its percentage of ionization?
8. Illustrate primary cell with an example.
9. The solubility of mercurous chloride in water at 25^o C is 1.0 x 10^-5 mol dm^-3 . What is its K_SP value at the same temperature?
10. What are surfactants? Give an example.

PART B

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

 

11  State Debye – Huckel limiting law. How is verified?What is its limitation?

12. Account for the abnormal mobilities of H₃O⁺ and OH^– ions in aqueous solution.
13. How is the solubility product of a sparingly soluble salt like AgCl is determined from EMF measurements?
14. Deduce Nernst equation from Butler – Volmer equation.
15. Write briefly on Helmholtz – Perrin model for an electrical double layer.
16. Distinguish between polarisable and non-polarisable electrodes with suitable examples.
17. Explain the dependence of pH on corrosion using Pourbaix diagram.
18. Write briefly on (i)Streaming potential (ii)Sedimentation potential
19. Calculate the thickness of ionic atmosphere in 0.10M calcium chloride solution in water at 27^o C . (Dielectric constant of water is 78.6)
20. Write a note on H₂ – O₂ fuel cell.
21. Explain Debye Falkenhagen effect.

PART C

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

 

22. Derive Butler – Volmer equation for a single step single electron transfer reaction and explain the low and high field approximations.
23. Discuss the Stern model for the electrode – electrolyte interface.
24. Derive the Debye – Huckel – Onsager equation .
25. a)Explain the amperometric method of estimation of silver nitrate.

b)What are electrocpillary curves?Explain its significance.

26. a)How does hydrogen over voltage arise?

b)Describe any two methods employed for the prevention of corrosion.

27.a)The equilibrium exchange current density for the reaction

H⁺  +  e ^–  →     H₂

on nickel  at 25^o C is 1.00 x 10^-5  A cm^-2 . What current density would be

necessary to attain a cverpotential of 0.1V ? (α = 0.5).

b)For Weston standard cell at 298K emf is 1.01032 V and temperature

co-efficient of  emf of the cell is -5.00 x 10^-5  VK^-1  . Calculate ∆ G , ∆H

and  ∆ S of the cell reaction.

 

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