LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY

FOURTH SEMESTER – APRIL 2008
CH 4808 – ELECTROCHEMISTRY
Date : 210408 Dept. No. Max. : 100 Marks
Time : 9:00 – 12:00
PART A
Answer ALL questions (10 x 2 = 20 Marks)
 Calculate the thickness of the ionic atmosphere in 0.10M aqueous solution of
barium chloride at 298K. (Dielectric constant of H_{2}O at 298K = 78.6).
 Derive the expression for the rate of an electrode reaction using Faraday’s law.
 An electrolyte of the type A_{2}B_{3} is 85% ionized in 0.01M solution.
What is the value of Vant’ Hoff i factor?
 What is Wien effect?
 Write Lipmann equation and explain the terms.
 What are the factors which affect the symmetry factor in an electrode reaction?
 Explain the various factors which influence the zeta potential.
 What is meant by stoichiometric number?
 Removal of oxygen from analyte is very essential in polarographic analysis.Why?
 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)
 Discuss the Born model for ion solvent interactions.
 Account for the abnormal conductance of H_{3}O^{+} ion in protic solvents.
 Explain the electrokinetic phenomena on the basis of irreversible thermodynamics.
 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).
 Distinguish between polarisable and nonpolarisable electrodes with
suitable examples.
 Discuss the mechanism of electroreduction of nitrobenzene.
 Explain how electrophoretic and relaxation effects affect the mobility of
an ion in solution.
 What are the advantages of DME? Mention two of its disadvantages.
 What is zeta potential? How is it determined?
 Deduce Nernst equation from Butler – Volmer equation.
 Explain: Halfwave potential and Residual current
 Calculate the mean ionic activity coefficient 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)
 Derive Debye Huckel Onsager equation. How is it verified?
What are its limitations?
 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.
 b) Discuss the high field and low field approximations of the above equation.
 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 coefficient of 7.2 x 10^{6} cm^{2} 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.
 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 I_{3}^{ – } ion
Step 1 I_{3}^{– } I_{2 }+ 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.