Dynamic techniques, in which current passes through the electrochemical cell, also are important electrochemical methods of analysis. In this section we consider coulometry. Voltammetry and amperometry are covered in section 11D. Coulometry is based on an exhaustive electrolysis of the analyte. By exhaustive we mean that the analyte is completely oxidized or reduced at the working electrode or that it reacts completely with a reagent generated at the working electrode. There are two forms of coulometry: controlled-potential coulometry, in which we apply a constant potential to the electrochemical cell, and controlled-current coulometry, in which we pass a constant current through the electrochemical cell.
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It consists of two independent electrode circuits that are connected with a common electrode. For the better results, three electrode systems re used. Working electrode: used for the deposition of the sample. Counter electrode: used as a current sink. Reference electrode: maintains the fixed potential despite the changes in solution components. Constant potential electrogravimeter Electrode Used in the Electrogravimetry The electrode used in the electrogravimetry should posses the following characters: It should be non-reactive.
It should be readily ignited to remove the organic matter. The commonly used electrode is the mercury cathode electrode for the deposition. This has the following advantages: It forms the amalgam with number of metals. It has a high hydrogen voltage. In this method, the precipitated elements are dissolved in the mercury.
This method is mainly used in the removal of the reduced elements. Electrodes Used in the successive deposition of the metals. Used in the simultaneous deposition of the metals. Used in the electro synthesis. Used in the purification process by removing the trace metals from the samples. Explain the electrolysis process in the electrogravimetry. What are the different types of electrogravimetric methods? What are factors affecting the deposition of the electrons? What are the different types of electrodes used in the electrogravimetry?
List out the applications of electrogravimetry.
7.2: Electrodeposition (Electrogravimetry)
Professor and Charles A. Dana Professor Chemistry and Biochemistry at Bates College No headers Electrodeposition or electrogravimetry are two terms used to describe the same analysis method. The general procedure is to use something like a platinum electrode and apply a constant reducing potential that is sufficient to plate out a solid metal. For example, this method could be used to plate out cadmium metal from solution by the reaction shown below. The difference in weight is solid cadmium and this amount can be related back to the concentration of cadmium in the original solution. Calculate potential values relative to a standard hydrogen electrode.
Electrogravimetry Electrogravimetry was briefly described above as an interference removal technique. This method employs two or three electrodes, just as in voltammetry. Either a constant current or a constant potential is applied to the preweighed working electrode. The working electrode corresponds to the indicator electrode in voltammetry and most other electroanalytical methods. A solid product of the electrochemical reaction of the analyte coats the electrode during application of the electric current or potential. After the assayed substance has been completely removed from the solution by the electrochemical reaction, the working electrode is removed, rinsed, dried, and weighed. The increased mass of the electrode due to the presence of the reaction product is used to calculate the initial concentration of the analyte.
6. Electrogravimetry & Coulometry (1).ppt
Potentiostatic coulometry[ edit ] Potentiostatic coulometry is a technique most commonly referred to as " bulk electrolysis ". The working electrode is kept at a constant potential and the current that flows through the circuit is measured. This constant potential is applied long enough to fully reduce or oxidize all of the electroactive species in a given solution. As the electroactive molecules are consumed, the current also decreases, approaching zero when the conversion is complete. It follows that, if three of the values are known, then the fourth can be calculated. Bulk electrolysis is often used to unambiguously assign the number of electrons consumed in a reaction observed through voltammetry. It also has the added benefit of producing a solution of a species oxidation state which may not be accessible through chemical routes.
11.3: Coulometric Methods