LOYOLA COLLEGE (AUTONOMOUS), CHENNAI –600 034

M.Sc., DEGREE EXAMINATION – CHEMISTRY

 FOURTH SEMESTER – NOVEMBER 2003

CH – 4803/1020 –  ELECTRO CHEMISTRY

01-11-2003                                                                                                     Max:100 marks

1.00 – 4.00

 

PART – A                                           (10X2=20 marks)

Answer ALL questions.

 

1. The limiting molar conductance of OHis highest among the anions – Explain.
2. Calculate the ionic strength of a mixture containing 20 mL of 0.1M lanthanum sulphate, 30 mL of 0.5 M magnesium nitrate and 50 mL of water.
3. In case of alkali halides the deviation from Debye Huckel Onsager equation is more marked as the atomic weight increases – Explain.
4. Calculate the limiting molar conductance of lanthanum ion if its mobility is 7.21 x 10^-8 m² V^-1 S^-1.
5. Write Lippmann’s first equation and mention its importance.
6. Draw the plot of current density vs applied potential for an electrolytic solution and hence indicate the discharge potential of an ion.
7. Mention the electrical properties that influence the rate of an electrochemical reaction.
8. Bring out the differences between symmetry factor and transfer coefficient.
9. What do you mean by non-polarisable electrode?
10. Define exchange current density.

 

PART – B                                           (8X5=40 marks)

Answer any EIGHT questions.

 

11. Calculate the instability constant of the complex formed in the reaction

Cu⁺² + 4 NH₃        [Cu (NH₃)₄]⁺²

Given Cu⁺² +2  Cu_(s)                                       E^o = 0.337 V

[Cu (NH₃)₄]²⁺ + 2    Cu_(s)  + 4 NH₃                E^o = -0.12 V.

12. 2 M lead nitrate solution freezes at -0.05^oC. Calculate its dissociation constant.  Cryoscopic constant of water is 1.86 kg K mol^-1.
13. The dissociation constant of chloroacetic acid is 1 x 10^-4. Will the degree of dissociation increase or decrease if 0.1 M KCl is added to 0.1 M chloro acetic acid?
14. Write notes on electro kinetic phenomena.
15. Discuss electrocapillary phenomena.
16. How is the limiting molar conductance of acetic acid determined using Debye Huckel Onsager – equation?
17. Compare the rates of reduction of Ag⁺, at over voltages -0.1 and +0.1 V, which has a symmetry factor, = 0.5.
18. Explain any one experimental method of determining the exchange current density.
19. State Butler – volmer equation for one electron process. Derive Nernst equation from it.
20. Determine the order of the reaction 2 H₃O⁺ + 2e 2 H₂O + H₂ in acidic medium.
21. Derive Tafel equation for cathodic process.
22. Define half wave potential. Show that it is a constant characteristic of the electro active species.

 

 

PART – C                                           (4X10=40 marks)

Answer any FOUR questions.

 

23. State the postulates of Debye Huckel theory and derive an expression for Debye Huckel length.
24. Derive Debye Huckel limiting law. How is it verified?  Mention its applications.
25. What are the features of Helmholtz Perrin model? What are its limitations?  How are these overcome in Stern’s model?
26. a) Derive the Butler – Volmer equation for a multistep electrochemical reaction.
27. b) Explain the condition under which the above equation reduces to simpler Butler –

Volmer equation.

27. a) A cathodic potential of 3V is applied to Cu²⁺ and Na⁺ solutions separately.  Calculate

the over potential of the two electrodes.

1. b) Explain any three applications of polarography.
2. a) Obtain an expression for limiting current on the basis of concentration polarization.
3. b) Write a note on
4. Cyclic voltametry
5. Amperometric titrations

 

 

 

 

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