Polarography is the technique with the help of which we can have qualitative as well as quantitative analysis by measuring the potential applied across cathode and anode and for each voltage applied we measure the current. Here the metallic ions are reduced on the surface of DME. The principle is the migration of ions (Cation) must take place on the surface of cathode due to concentration gradient and not due to potential gradient concentration gradient means change in concentration in the vicinity of cathode and bulk As soon as drop of Hg is formed in the electrolyte, it acts cathode. The metallic ions which are around the cathode will be attracted on cathode due to electrostatic attractions and are reduced over D.M.E. So the concentration of electrolyte decreases in the vicinity of cathode. The other neighboring ions will move and gets deposited on DME. The complete reduction of metallic ions on the D.M.E. involves the following three steps:
1. The migration of the ions from the interior of the solution to the electrode surface.
2. The reduction of ions on the cathode to form neutral atoms.
3. The deposited atoms are converted into crystal lattice structure.
The first step is slow and last two steps are fast. Therefore, the rate determining step is one which is slow. The current obtained in the galvanometer depends on rate of migration of ions from the interior of the solution. The electrolysis is carried out using cathode DME. The other electrode is having large surface area. OR SEC
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