LOYOLA COLLEGE (AUTONOMOUS), CHENNAI –600 034
M.Sc., DEGREE EXAMINATION – CHEMISTRY
FOURTH SEMESTER – NOVEMBER 2003
CH – 4803/1020 – ELECTRO CHEMISTRY
01-11-2003 Max:100 marks
1.00 – 4.00
PART – A (10X2=20 marks)
Answer ALL questions.
- The limiting molar conductance of OHis highest among the anions – Explain.
- Calculate the ionic strength of a mixture containing 20 mL of 0.1M lanthanum sulphate, 30 mL of 0.5 M magnesium nitrate and 50 mL of water.
- In case of alkali halides the deviation from Debye Huckel Onsager equation is more marked as the atomic weight increases – Explain.
- Calculate the limiting molar conductance of lanthanum ion if its mobility is 7.21 x 10-8 m2 V-1 S-1.
- Write Lippmann’s first equation and mention its importance.
- Draw the plot of current density vs applied potential for an electrolytic solution and hence indicate the discharge potential of an ion.
- Mention the electrical properties that influence the rate of an electrochemical reaction.
- Bring out the differences between symmetry factor and transfer coefficient.
- What do you mean by non-polarisable electrode?
- Define exchange current density.
PART – B (8X5=40 marks)
Answer any EIGHT questions.
- Calculate the instability constant of the complex formed in the reaction
Cu+2 + 4 NH3 [Cu (NH3)4]+2
Given Cu+2 +2 Cu(s) Eo = 0.337 V
[Cu (NH3)4]2+ + 2 Cu(s) + 4 NH3 Eo = -0.12 V.
- 2 M lead nitrate solution freezes at -0.05oC. Calculate its dissociation constant. Cryoscopic constant of water is 1.86 kg K mol-1.
- The dissociation constant of chloroacetic acid is 1 x 10-4. Will the degree of dissociation increase or decrease if 0.1 M KCl is added to 0.1 M chloro acetic acid?
- Write notes on electro kinetic phenomena.
- Discuss electrocapillary phenomena.
- How is the limiting molar conductance of acetic acid determined using Debye Huckel Onsager – equation?
- Compare the rates of reduction of Ag+, at over voltages -0.1 and +0.1 V, which has a symmetry factor, = 0.5.
- Explain any one experimental method of determining the exchange current density.
- State Butler – volmer equation for one electron process. Derive Nernst equation from it.
- Determine the order of the reaction 2 H3O+ + 2e 2 H2O + H2 in acidic medium.
- Derive Tafel equation for cathodic process.
- Define half wave potential. Show that it is a constant characteristic of the electro active species.
PART – C (4X10=40 marks)
Answer any FOUR questions.
- State the postulates of Debye Huckel theory and derive an expression for Debye Huckel length.
- Derive Debye Huckel limiting law. How is it verified? Mention its applications.
- What are the features of Helmholtz Perrin model? What are its limitations? How are these overcome in Stern’s model?
- a) Derive the Butler – Volmer equation for a multistep electrochemical reaction.
- b) Explain the condition under which the above equation reduces to simpler Butler –
- a) A cathodic potential of 3V is applied to Cu2+ and Na+ solutions separately. Calculate
the over potential of the two electrodes.
- b) Explain any three applications of polarography.
- a) Obtain an expression for limiting current on the basis of concentration polarization.
- b) Write a note on
- Cyclic voltametry
- Amperometric titrations