LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

LM 52

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)

 

1. The deviation from Debye Huckel Onsager equation is more marked as the atomic weight of alkali metal halide increases – Explain.
2. Which of the following will have greater ion – ion interaction?

(i) 0.01 m KCl             (ii) 0.01 m CuSO₄.

3. and  are 0.337 and 0.521V respectively. Is it easier to

oxidize  cu to cu⁺ or cu to cu⁺²?

1. According to Stern’s model, how do ions congregate in solution?
2. Define potential of zero charge.
3. Derive the expression for the electrochemical reaction rate on the basis of Faraday’s laws of electrolysis.
4. Define exchange current density of and electrode.  How is it related to its polarisability?
5. Indicate the potential range at which an electrode shows ohmic and non ohmic behaviours.
6. Define transfer coefficient.  How can it be determined experimentally?
7. 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)

 

1. 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 15^oC.
2. Derive an expression for the Debye Huckel length.
3. Determine the solubility of BaSO₄ in (i) 0.1m BaCl₂ and (ii) 0.1m KNO₃. K_sp of BaSO₄ is 1 x 10^-10 mol² dm^-6.
4. Calculate the limiting molar conductance of lanthanum sulphate from the following data:

1. What are electro capillary curves?  How is it influenced by surfactants?  Explain.
2. Write notes on electro-osmosis.
3. The exchange current density, I_o 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.
4. 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.
5. 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).
6. 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

1. Discuss any five types over potential for an electrode system.
2. 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)

1. Derive Debye Huckel Onsager equation.  How is it verified?
2. Give an account of ‘Parallel Plate Consdensor Model’ to explain the double layer structure.
3. Define ion-ion interaction.  Derive an expression for ion-ion interaction interms of chemical potential.
4. a) Derive the Butler-volrmer equation relating current and over potential for a

simple  electrode system.

1. b) Deduce Ohm’s law equation from the above relation.

1. a) Explain the factor deciding electrode rectification?

1. b) Discuss Butler-Volmer equation for different value of over potential.

1. 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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