ELECTROGRAVIMETRY

ELECTROGRAVIMETRY is part of analysis.

1. ELECTROGRAVIMETRY

2. EIECTROGRAVIMERY INTRODUCTION Elctrogravimerty is a method used to separation and qantity ion of substance ,usually a metal. In this process ,the analyte solution is electrolyzed . Electrochemical reduction causes the analyte to be deposited on the cathode . The cathode is weight before and after the experiment ,and weighinig by difference is used to calculate the amount of analyte in the original solution . Contolling the potential of the electrode is important to ensure that only the metal being analyzed will be deposited on the electrode.

3. PRINCIPLE the main principle involed in this method is the deposition of the solid on an electrode from the analyte solution .

4. TYPES OF ELECTROGRAVIMETRY there are two types electrogravimetry method . Constant current electrolysis. Constant potential electrolysis. constant current electrolysis. in this process the current is kept constant ,and potential is increased . Here no contole of the potential of the working elwctrode is exercised ,and the aplied cell potential is held at a more or less constant level but provide a large enough current to complete the electolysis in a reasonable lenth of time . And a fixed ammount of the current can be passing between the anode and cathode .

5. The limitation of constant current electrolysis is it cannot be used for the separation of ion in solution containing single species.

6. 2 Constant potential electrolysis . ti is the simplest way of performing an analytical electrolysis is to maintain the applied cell potential at acontant value. it is more used in the separation of the compounts from a mixture in which the decomposition potential are not widely separate . A fairy large voltage is applied to working electrode order to force a constant relatively large current flow through the cell. The current is often on the order ot milliamps (ma) instend of microamps (micrometer a),as a typically the case in controlles potential electrogravimery .

7. Three electrode system are used. Working electrode : used for the deposition of the sample. Counter electrode: used for the current sink. Reference electrode: maintains the fixed potential despite the change in solution compounts .

8. for example : the determination of copper from an acidic solution (either nitric acid or sulphuric acid solution or mixture of two acids) at constat current . Suppose an EMFof 2-3v is applied then the reaction taking placeare given below. At cathode : cu+ 2 + 2e - cu at Anode : 40H - O 2 + 2H 2 O=4e -

9. Electrodeposition is governed by ohms law and faradays two law of electrolysis. Ohms law from ohms law the relation between current ,voltage and resistance is given by, I =V/R Faradays law A . In electrolysis the amount of substance liberated at the electrode of a cell is directiy proportional to theamonut of electricity which passes throught the solution. M Q M=Z Q M= Z I T where , M = mass of the substance liberated at the electrode.

10. Z= electrochemical equvient . I= current in ampere. T= time in second. B. The mass of substance liberated is directly proportional to the relative weight of those substance at a particular quqntity of elecricity applied, m 1 /z 1 = m 2 / Z 2 In electrogravimetry the determination of metal is carried out by above two procedures ,at constant or with controlled potential procedure ,but constant is limited.

11. INTRUMENTATION . the apparatus for an analytical electrodeposition with out cathode potential control consist of a sutaible cell and direct current supply. The voltage applied to the cell is controlled by the variable resistance R . A current metal and a voltmeter indicate the approximate current and voltage . The voltage is then maintained at about the initial level until the deposition judged to the complete. APPLICATION used in the succesive deposition of the metals . Example cu , bi, zn ,and sn .

12. Used in the simulationeous deposition of the metal . Used in the electro synthesis. Used in the purification process by removing the trace metal from the sample

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