LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
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M.Sc. DEGREE EXAMINATION – CHEMISTRY
FOURTH SEMESTER – APRIL 2007
CH 4805 / CH 4808 – ELECTROCHEMISTRY
Date & Time: 18/04/2007 / 9:00 – 12:00 Dept. No. Max. : 100 Marks
PART – A
Answer ALL the questions (10 x 2 = 20 marks)
- The deviation from Debye Huckel Onsager equation is more marked as the atomic weight of alkali metal halide increases – Explain.
- Which of the following will have greater ion – ion interaction?
(i) 0.01 m KCl (ii) 0.01 m CuSO4.
- and are 0.337 and 0.521V respectively. Is it easier to
oxidize cu to cu+ or cu to cu+2?
- According to Stern’s model, how do ions congregate in solution?
- Define potential of zero charge.
- Derive the expression for the electrochemical reaction rate on the basis of Faraday’s laws of electrolysis.
- Define exchange current density of and electrode. How is it related to its polarisability?
- Indicate the potential range at which an electrode shows ohmic and non ohmic behaviours.
- Define transfer coefficient. How can it be determined experimentally?
- Define diffusion over potential. Explain how the concentration over potential can arise mainly due to diffusion.
PART – B
Answer any EIGHT questions (8 x 5 = 40 marks)
- Consider the cell, cd/cdcl2 . 2½ H2O/Agcl(s)/Ag(s). The emf of the cell at 15C is 0.67531and the temperature coefficient of emf is –0.00065 Vdeg-1. Calculate DG, DS and DH for the above cell reaction at 15oC.
- Derive an expression for the Debye Huckel length.
- Determine the solubility of BaSO4 in (i) 0.1m BaCl2 and (ii) 0.1m KNO3. Ksp of BaSO4 is 1 x 10-10 mol2 dm-6.
- Calculate the limiting molar conductance of lanthanum sulphate from the following data:
- What are electro capillary curves? How is it influenced by surfactants? Explain.
- Write notes on electro-osmosis.
- The exchange current density, Io of a certain electrode and its symmetry factor, b are 1.35 mA and 0.45. Calculate is cathodic current at an over potential of 300mV.
- Calculate the magnitude of the anodic Tafel slope of the plot of logi vs h for an electrode having its anodic transfer coefficient 1.5 at 298K.
- Calculate the minimum potential required for the discharge of Ag+ from its 1x 103 M solution at 298K (The SRP of Ag+/Ag system = 0.80V).
- The reduction of Fe2+ to Fe follows the following mechanism
Fe2+ + H2O ⇄ FeOH+ + H+ eq conts K1 ….. (1)
FeOH + e ⇄ FeOH eq conts K2 ….. (2)
FeOH +H+ + e ⇄ Fe + H2O eq conts K3 ….. (3)
Determine the following parameters if step-2 is rds.
= ; ; n ; r ; and
- Discuss any five types over potential for an electrode system.
- State the following relation for polarography connecting
- EMF & current density
- Current density & concentration
Explain their applications.
PART – C
Answer any FOUR questions (4 x 10 = 40 marks)
- Derive Debye Huckel Onsager equation. How is it verified?
- Give an account of ‘Parallel Plate Consdensor Model’ to explain the double layer structure.
- Define ion-ion interaction. Derive an expression for ion-ion interaction interms of chemical potential.
- a) Derive the Butler-volrmer equation relating current and over potential for a
simple electrode system.
- b) Deduce Ohm’s law equation from the above relation.
- a) Explain the factor deciding electrode rectification?
- b) Discuss Butler-Volmer equation for different value of over potential.
- The electrochemical reduction of I to I proceeds by a three step mechanism viz., fast equilibrium dissociation of (i) I to I2 & I (ii) I2 to I (iii) followed by the slow reduction of the dissociated I atoms to I. Write the mechanism of the reaction and hence determine the transfer coefficient for the reaction.
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