CH 4808 / 4805 / 4803 – ELECTROCHEMISTRY

Date & Time: 21/04/2009 / 9:00 – 12:00 Dept. No. Max. : 100 Marks

Part–A (20 Marks)

Answer ALL questions (10 x 2 = 20)

Calculate the ionic strength of a solution obtained by mixing 50 ml of 0.02 M
Na₂SO₄ and 50 ml of 0.02 M cerium (III) sulphate solutions.
Mention the factors affecting the thickness of the ionic atmosphere of an electrolytic solution.
E^°_red of Au⁺/Au is 1.68 V, E^°_red Au³⁺/Au is 1.50 V. Calculate E^°_oxi of Au⁺/Au³⁺
at 25°
Calculate the zeta potential of a colloidal particle in aqueous solution that has an
electrophoretic mobility of 1.1 10^-8 m² s^-1 V^-1. The coefficient of viscosity of water is 8.91 x 10^-4 kg m^-1 s^-1 and Î = 78.3.
What is ‘Dorn Effect’?
Draw the general pattern of the plot of current density vs overvoltage for an electrode having symmetry factor 0.75.
What do you mean by the high field approximation of the Butler-Volmer equation.
The diffusion current of a certain metal ion at 3 × 10^-2mM is 3.3µA calculate its diffusion current at 6.9 × 10^-2mM concentration.
Bring out the difference between voltammetry and polarography.
Differentiate between half wave and standard reduction potentials.

Part-B (40 Marks)

Answer ANY EIGHT questions (8 x 5 = 40)

Deduce Lippmann’s equation and mention its significance.
Explain the influence of electrolytes on electrokinetic effects.
The thermodynamic dissociation constant of a weak acid (HA) at 25°C is 2 10^-5.
What is the degree of dissociation of 0.1 M acid in 0.01 M KNO_{3 (aq)} solution?
Calculate K_h for NH₄Cl if the EMF of the cell.

Pt½H₂(1 atm)½NH₄Cl(0.2M) ½½ KCl(1M)½Hg₂Cl₂½Hg

at 25° C is 0.574 V and E°_red of calomel electrode is 0.28 V.

Determine the potential due to ionic atmosphere around cation at 25° C for
10^-3M CaCl₂(aq) if Î₀ = 8.854 ´ 10^-12 C²J^-1m^-1 and dielectric constant of water is
3.
Explain Wien’s effect and its importance in the study of strong electrolytes.
Electrolysis of a solution of Cu²⁺ produces 16 mg of Cu in 2 minutes. Calculate the rate of the reaction.

What do you mean by non polarisable electrode? How is it related to its current density?
Calculate the current density across an electrode (β = 0.45) at an applied potential of 0.23V if its equilibrium potential is 0.09V
Explain migration and diffusion currents. Which current is significant in poloragraphy? How is it achieved?
The dissolution of iron follows the following mechanism:

Fe + H₂O FeOH + H⁺+ e^– ; Eq Const K₁……….……1

FeOH FeOH⁺ + e^{– ;}Eq Const K₂……….…….2

FeOH⁺ + H⁺ Fe²⁺+ H₂O ; Eq Const K₃…………….3

Determine its transfer coefficients if step-2 is the rate determining step.

Part-C (40 Marks)

Answer ANY FOUR questions (4 x 10 = 40)

What is the need for a model on electrical double layer? Explain Helmohlltz-Perrin model and mention its defects. (3 + 5 + 2)
(a) Mention the assumptions of Debye-Huckel theory and explain any one
application of Debye-Huckel limiting law equation. (3 + 4)

(b) What is the need to modify the limiting law equation. (3)

Derive the relation between current density and applied potential for an electrode undergoing multistep multi electron reaction
Define limiting current. Derive an expression for it relating to concentration on the basis of the concept of concentration polarization.
Explain the following with suitable examples and figures.