Polarometery

polarography

1. Polarography Presented by : Ajay Hage and Ganesh G huge

2. Content Introduction Principle Types of current Construction and working Half wave potential Ilkovic. Equation Application

3. Introduction Discovered by Jaraslove Heyrosky in 1922, Who received Nobel prize in chemistry in 1952. The term polarography is applied to the current voltage curve when dropping mercury electrode is used and indicator electrode. This method comes under the category of voltammetry techniques.

4. Principle: Polarography can be applied by increasing negative potential between polorisable. and depolrisable. electrode. Current voltage curve is recorded in sigmoid shape The instrument which is use which is known as polarograp. The current voltage curve is recorded which is known as polarogram. Polarogram

5. Polarogram:

6. Types of current : Residual current Migration current Diffusion current Limiting current

7. Residual current: It is the sum of the faradic current and condenser current. Current produced by traces of the impurities or reduction of the impurities. Condenser Current produced by Helmholtz double layer. Residual current is denoted by (ir).

8. 2: Migration current Migration current is due to cation from the bulk of the solution towards the Cathod due to diffuse force. This current is due to migration of oxidizable and reducible ion which is proportional to the potential gradient. This can be removed by the addition of supporting electrolyte solution.

9. 3 : Diffusion current Diffusion current is due to actual diffusion of eletroreduciable ion from the bulk of sample to the surface of the mercury droplet due to concentration gradient. Various factors can be affected by the diffusion of current.

10. 4: limiting current. Beyond a certain potential the current reaches a steady value called as limiting current. At this point the rate of diffusion of ion is equal to rate of reduction. State of electrode is said to be concentration polarised.

11. polarography apparatus:

12. Construction and working: Dropping mercury electrode. Supporting electrolyte. Mercury pooled Capillary tube.

13. Dropping mercury electrode: The indicator electrode is use for the analyte of sample in the response of potential. Dropping mercury electrode is use as indicater electrode.gradully increasing negative potential can be applied easily. Known as working electrode. The basic principles of this dropping mercury electrode is to control mercury flow through the capillary closed the neddle valve.

14. Drop of mercury:

15. Advantages It provides a smooth and fresh surface for the reaction. Mercury forms amalgam with most metals. Mercury has high hydrogen overvoltage. Each drop remains unaffected and does not contaminated by the deposit ed metals. It useful the range of +0.4 to -1.8 volt.

16. Disadvantages: Surface area of drop of mercury has never constant. Mercury has a poisonous. Applied voltage produces change in surface tension and change in drop size.

17. Capillary tube: The capillary is glass tube and internal diameter is 20-50u and connect ed to mercury reservoir. By adjusting the height of the reservoir the drop time can also adjusted. The drop size depends on the bore size of the capillary.

18. Mercury pooled: A large pooled of mercury at bottom of the cell is a anode and act as reference electrode. Saturated calmol electrode is also use. By connecting the pooled of mercury.

19. IIkovic equation The diffusion current at the SAME is given by llkovic equation: id= 607n c m t Various factors can affect the llkovic equation. The quantities of mass ,and time will vary with the capillary and the pressure of the mercury.

20. Half wave potential: Half wave potential is defined as the difference between the total current to the total residual current which is equal to the one half of the limiting current. This can be obtained from theCVC. This can be mainly use for the identification of the substance.

21. Application : Qualitative and quantitative analysis. Turbid and colour sample will be analysed. Mixture of sample will be analysed or without separation of sample will be analysed. Inorganic and organic sample can be analysed. Small amount of sample can be analysed.

22. Thanks