LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY
FOURTH SEMESTER – APRIL 2008
CH 4808 – ELECTROCHEMISTRY
Date : 21-04-08 Dept. No. Max. : 100 Marks
Time : 9:00 – 12:00
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 H2O at 298K = 78.6).
- Derive the expression for the rate of an electrode reaction using Faraday’s law.
- An electrolyte of the type A2B3 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.
Answer any EIGHT questions (8 x 5 = 40 Marks)
- Discuss the Born model for ion- solvent interactions.
- Account for the abnormal conductance of H3O+ 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 non-polarisable electrodes with
- Discuss the mechanism of electro-reduction 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: Half-wave potential and Residual current
- Calculate the mean ionic activity co-efficient in 0.01M aqueous solution of
potassium ferrocyanide at 298K using Debye – Huckel limiting law.
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 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.
- 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 -0.10o C If Kf 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 I2 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.