1. Amperometric Titrations By
Satish Pradhan Dnyanasadhana College, Thane.
Department of Chemistry T.Y.B.Sc. Analytical Chemistry Paper-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
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
Titrand
Titrant
Product
Out of these three one is reducible

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

11. Titrant is reducible but Titrand and product not .
Mg+2
Titrant
8- hydroxy quinoline .
Product
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. Ex.Mg+2 v/s 8-Hydroxy quinoline -1.6 V(SCE)
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
Pb+2
Titrant
K2Cr2O7.
Product
The titration is performed 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 is performed 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. Volume of Titrant added
Ttrand and titrant both are reducible but product not Ex.Pb+2 v/s K2Cr207 at constant
potential V (SCE)
Diffusion current
Equivalence point
Volume of Titrant added

17. Advantages of Amperometric Titration1
Method is accurate and equivalence point is obtained by means of graph 2
The electrode surface is continuously renewed ,current values are reproducible. 3
Amperometric titrations can be carried out at dilutions at which Potentiometry, or ordinary titrations method can not work 4
Readings near the end points are not of importance in this method , so precipitations titrations can be carried out.

18. Disadvantages of Amperometric Titration1
Considerable time is required to remove dissolved oxygen before and during the titration 2
The titrations can be carried out at potentials more negative than 2 volts since hydrogen will be evolved. 3
Co precipitations can give inaccurate results.

19. Thank you