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Describe the construction and working of the calomel electrode. |
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Answer» Solution :The calomel electrodeis widelyused as a secondaryreference ELECTRODE. (1) Construction : (1) The calomel electrodeconsists of a glass vessel having side ARM B, for addingmercuryand other constituentsand arm C, for dippingit in any desired solution. A platinum WIRE A is usedfor an electricalcontact. Over this platinum wire are placedpure mercury. a paste of Hg and `Hg_(2)Cl_(2)`(mercurous chloride, i.e., the calomel and saturated KCL solution so as to fill the vessel and the arm C as shown in figure. (2) The potential developed on this electrodedepends upon the concentrationof chlorideions. (2) Representationof the calomel electrode : `KCl_(("sat")) |Hg_(2)Cl_(2(s))| Hg_((l))` KCl solution of differentconcentrationcan alsobe used.  (3) Working: If the electrodeacts as anodethen, Oxidation : The followingreactiontakes place. `2Mg_((l)) rarr Hg_(2)^(2+) + 2e^(-)` `Hg_(2)^(2+) + 2Cl^(-) rarrHg_(2)Cl_(2(s))` Thus overall reaction is , `2Hg_((l)) + 2Cl_((aq))^(-) rarr Hg_(2)Cl_(2(s)) rarr Hg_(2)Cl_(2(s)) + 2e^(-)` If the electrodeacts as cathode then, Reduction : The reduction reaction is represented by `Hg_(2)Cl_(2(g)) +2e^(-) rarr 2Hg_((l)) +2Cl_((aq))^(-)` (4)Applications of calomel electrode : It is used to determinethe potentialsof other electrodes by developing a reversible galvanic cell by combiningwith experimental electrode. (5) Advantage : (1) The calomalelectrode is one of the most widelyused referenceelectrodes. (2) It has constantreproducible potential. (3) It is handy, compact and easy to transport. (4) It has very small temperaturecoefficient ofpotential. |
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