LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 15

FOURTH SEMESTER – APRIL 2008

CH 4502 – ELECTROCHEMISTRY

 

 

 

Date : 26/04/2008                Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

PART – A

 

Answer ALL the questions                                                                            (10 x 2 = 20 marks)

 

1. Write down the reactions taking place at the anode and cathode separately

Cu½ Cu²⁺ ½½ Ag⁺ ½ Ag

1. What is meant by primary reference electrode?
2. What is LJP?  How can it be minimized?
3. Explain why quinhydrone electrode cannot be used for alkaline solution.
4. Calculate the ionic strength of 0.01 M Cu SO₄ solution.
5. Compare the transference numbers of chloride ion in HCl and NaCl.
6. Mention any two advantages of conductometric titrations.
7. What is meant by activity of an electrolyte?  How is it related to activity coefficient of an electrolyte?
8. Define overvoltage.
9. What is concentration polarization?

 

PART – B

 

Answer any EIGHT questions                                                                 (8 x 5 = 40 marks)

 

1. Describe the following types of electrodes with examples and write the electrode reactions.      a) Metal – Metal ion electrode  b) gas electrode.

 

1. Describe the construction and working of a calomel electrode.

 

1. How will you determine the standard electrode potential of zinc electrode?

 

1. The standard oxidation potentials of Ce³⁺– Ce⁴⁺ and Fe²⁺– Fe³⁺ systems are – 1.61 and

-0.771 respectively.  Calculate the equilibrium constant at 25^oC for the reversible process     Fe²⁺ + Ce⁴⁺  Ce³⁺ + Fe³⁺.

1. Describe any one method of determination of pH of a solution by EMF measurement.

 

1. Derive expressions for DG, DH and DS in terms of EMF of a cell.

 

1. Differentiate between a strong and a weak electrolyte from the variation of conductance with concentration.

 

1. Calculate the equivalent conductance at infinite dilution of NH₄OH, if the equivalent conductance at infinite dilution of Ba(OH)₂, BaCl₂ and NH₄Cl are 228.8, 120.3 and 129.8 ohm^-1 cm² eqiv^—1 respectively.

 

1. How is K_a of a weak acid determined by conductance measurement?

 

1. Discus the conductometric titrations of a) a strong acid with a strong base b) a strong acid with a weak base.

 

1. What are the applications of overvoltage?

 

1. How is the decomposition voltage in an aqueous solution measured?

 

 

PART – C

 

Answer any FOUR questions                                                                        (4 x 10 = 40 marks)

 

1. Define EMF.  How is solubility product of a sparingly soluble salt determined from EMF measurement?
2. What is a standard cell?  Discuss the working of Weston standard cell.
3. What are concentration cells? Derive an expression for the EMF of an electrolyte concentration cell without transference.
4. The cell Cd½Cd Cl₂ ½½ Ag Cl ½ Ag  has an emf of 0.675 V at 25^oC and the temperature coefficient of emf is – 0.00065 V deg^-1.  Calculate DG, DH and DS for the cell reaction.
5. What is meant by transference number of an ion?  Describe the moving boundary method for the determination of transference number of an ion.
6. a)  Give a account of Debye – Huckel theory of strong electrolytes.                         (6)

1. b) Discuss the principle of polarography. (4)

 

 

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