LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 40

FOURTH SEMESTER – APRIL 2006

                                               CH 4805/CH 4803 – ELECTROCHEMISTRY

 

 

Date & Time : 20-04-2006/FORENOON     Dept. No.                                                       Max. : 100 Marks

 

 

 

Part–A (20 Marks)

 

Answer ALL questions (10 x 2 = 20)

1. Calculate the thickness of ionic atmosphere in 0.1M aqueous lanthanum sulphate.
2. Compare the ion-solvent interaction of the following
   1. 1M aq KCl
   2. 1M aq Al₂(SO₄)₃
3. λ _H+ is the highest among cations in aqueous solution. Why?
4. How is the capacitance related to the thickness of double layer in Helmholtz Perrin

model?

5. What are surfactants? Give example.
6. What do you mean by a polarisable electrode? State the condition for its ideal

polarisability.

7. What is reaction resistance? Calculate its value of an electrode having equilibrium

current density  2 .08 μA cm.

8. Nernst equation is a special case of Butler-Volmer equation.Explain.
9. Determine whether Cu form 0.01 M Cu²⁺ will be deposited or not.

( SRP :  Cu²⁺/ Cu = 0.34V )

10. Obtain the relation between rate and current density of an electro-chemical reaction

from Faraday’s laws.

Part-B (40 Marks)

 

Answer any EIGHT questions (8 x 5 = 40)

11. 11. What are electro capillary curves? What is its importance?
12. Derive an expression for the interfacial tension applying parallel plate condenser

model.

13. Apply Born’s model to find out the energy of ion solvent interaction.
14. 14. Discuss the evidences for the existence of ionic atmosphere.
15. 15. The measured emf for the cell Ag, AgBr,KBr || Hg₂Br₂ | Hg are 0.06839V at 25ºC

and 0.07048V at 30ºC. Write the reaction involved and calculate ∆H, ∆G and ∆S

for the reaction at 25ºC

16. A 0.2m lead nitrate solution freezes at -0.10ºC. Calculate the dissociation constant

if K_f of water is 1.86 K molal^-1

17. Derive the Butler-Volmer equation for a one electron electrode process.
18. 18. Define transfer coefficient. How is it determined experimentally?
19. 19. The reversible potential and c.d of an electrode are 0.22 V and 7.2×10 ^-4 A cm^-2

        respectively. Calculate the c.d across it   at 0.74 V if it has 40% cathodic tendency.

 

20. 20. The tafel anodic and cathodic slopes of “applied potential vs logi ” of an

electrode process were found to be 0.04 & 0.12 respectively.  Calculate the

ransfer coefficients.

 

21. 21. Explain the applications of Tafel equations.

 

22. 22. The exchange current density of Pt/Fe, Feis 2.5 mA cm. Calculate the

current density across the electrode at 25C maintained at 1V when [Fe] = 0.1

M and [Fe]= 0.2 M (SRP = 0.77IV, β = 0.58)

 

Part-C (40 Marks)

 

Answer any FOUR questions (4 x 10 = 40)

 

23. 23. Discuss sterns model of double layer structure.
24. 24. Describe ‘Electrokinetic Phenomena’.
25. 25. Derive Debye Huckel limiting law. How is it verified?
26. 26. For the system Pt /Fe³⁺, Fe²⁺ at 298K the i were measured as shown below:

(mV):             50       80      100     120        150     200

(mA cm)   :  8.01  16.1    25.17    41         82.4   264

Evaluate  i_o and β

27. 27. Consider the following mechanism for the deposition iron.

 

Fe²⁺ + H₂O           FeOH⁺ + H⁺   eq const K₁ ……. (1)

 

                                   FeOH⁺ + e            FeOH             eq const K₂ ……. (2)

 

FeOH + H⁺ + e          Fe + H₂O    eq const K₃   ……. (3)

 

Derive the expression for rate if step-2 is rds

28. Discussion of Butler -Volmer equation for different values of over potentials.

 

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