Satish Pradhan Dnyanasadhana College, Thane .

1. SatishPradhan Dnyanasadhana College, Thane. Department of ChemistryT.Y.B.Sc. Analytical ChemistryPaper-IV Sem-VI Amperometric Titrations By Dr.Bhagure G.R.

2. Contents • 1.3 Amperometric titrations (04L) • 1.3.1 Comparison between Amperometry and voltammetry. • 1.3.2 Basic principle of amperometry • 1.3.3 Rotating platinum electrode: Instrumentation, advantages and limitations. • 1.3.4 Amperometric titrations: Examples and titration curves. • 1.3.5 Applications, advantages and limitations

3. Rotating Platinum electrode Flange inward to inward to prevent mercuring from being thrown out Glass tubing Copper Wire Mercury reservoir Hole Stem to make electrical contact mercury reservoir Platinum Wire Direction of rotation

4. Diffusion current is directly proportional to concentration

5. Diffusion Current uA 20 40 60 80 100 Concentration

6. Principle of Amperometric titrations • From polarogram it can be seen that , the diffusion current ( = limiting current - residual current) is proportional to the concentration of the electro-active material in the solution. If some of the electro-active material is removed by interaction with reagent, the diffusion current will decrease. This is the fundamental principle of amperometric titrations. The observed diffusion current at a suitable applied voltage is measured as a function of the volume of the titrant added. the end point is the point of intersection of two lines giving the change of current before and after the equivalence point. Some advantages of amperometric titrations may be mentioned:

7. Principle of Amperometric titrations Out of these three one is reducible

8. Titrand is reducible but Titrant and product not . The titration can be performed at fixed potential -0.8 Volt v/s saturated calomel

9. 1. Titrand is reducible but titrant and product not: • When solution containing Pb+2 ion is titrated against SO4-2 ion. A precipitate of PbSO4 is formed. The titration can be performed at fixed potential -0.8 Volt v/s saturated calomel electrode. As titration is proceeds concentration of Pb+2 ion decreases and diffusion current also decreases till it becomes minimum at equivalence point. The diffusion current remains constant beyond end point. The values of diffusion current is plotted against the volume of titrant added .The resulting titration curves is straight line leveling off at end point . The intersection of two extra plotted portions of the curves gives the end point.

10. A) Ttrand is reducible but titrant and product not. Ex.Pb+2 v/s SO4-2 at constant potential -0.18 V (SCE) Diffusion current Equivalence point Volume of Titrant added

11. Titrant is reducible but Titrand and product not . The titration can be performed At constant potential of -1.6 volt. v/s saturated calomel

12. 2. Titrant is reducible but titrand and product not : • When solution containing Mg+2 ion is titrated against with the reducible species such as 8- hydroxy quinoline . At constant potential of -1.6 volt. In this titration the current is steady till the end point because Mg+2 ion does not undergoes reduction. Beyond the end point the 8- hydroxy quinoline undergoes reduction. As its concentration increases diffusion current also increases.

13. B) Titrant is reducible but titrand and product not Ex.Mg+2 v/s 8-Hydroxy quinoline -1.6 V(SCE) Diffusion current Equivalence point Volume of Titrant added

14. Titrand and titrant both are reducible but product not The titration isperformed at potential of -0.8 Volt v/s SCE

15. 3. Titrand and titrant both are reducible but product not : • When solution containing Pb+2 ion is titrated against K2Cr2O7. The titration isperformed at potential of -0.8 Volt v/s SCE . Diffusion current is decreases due to removal of Pb+2 ion. The current is minimum at the end point. On further addition of the titrant the current once again increases. V shaped curve is obtained.

16. Ttrand and titrant both are reducible but product not Ex.Pb+2 v/s K2Cr207 at constant potential -0.8 V (SCE) Diffusion current Equivalence point Volume of Titrant added

17. Advantages of Amperometric Titration

18. Disadvantages of Amperometric Titration

19. Thank you