Describe the Construction & Working of Calomel electrode
Answers
Calomel electrode is the mercury-mercurous cbloride electrode. It consists of glass vessel having bent side tube. Pure mercury is placed at the bottom of the tube. Which is covered with a paste of mercury- mercurous chloride (Hg+Hg2Cl2) i.e., calomel. The remaining portion of the cell is filled with a solution of normal (1N) or decinormal (0.1N) or saturated KCl. A platinum wire sealed into a glass tube is dipped into mercury layer is used to provide the external electrical contact. The side tube is used for making electrical contact with a salt bridge. The electrode can be represented as Hg(l)/Hg2Cl2 (s) / Cl- The calomel electrode can act as anode or cathode depending on the nature of other electrode of the cell. When it acts anode, the electrode reaction is 2Hg(l) → Hg22+ + 2e- Hg22+ + 2Cl- → Hg2Cl2 --------------------------------------------------------------- 2 Hg + 2Cl- → Hg2Cl2 + 2e- (Oxidation reaction) When it acts as cathode, the electrode reaction is, Hg22+ + 2e-→ 2 Hg Hg2Cl2 → Hg22+ + 2Cl- ________________________________________ Hg2Cl2 + 2e- → 2Hg (l) + 2 Cl- [Reduction reaction] The net reversible electrode reaction is, Hg2Cl2(s) + 2e- <════> 2 Hg (l) + 2 Cl- Electrode potential is given by E = Eo – 2.303 RT/2F log [Cl-]2 = Eo -0.0591 log [Cl-] at 298 K The electrode potential is decided by the concentration of chloride ions & the electrode is reversible with chloride ions at 298K, the electrode potentials are as follows. 0.1N KCl electrode (0.334V) 1 N KCl electrode (0.281 V) Saturated KCl electrode (0.2422 V)
Calomel Electrod is the mercury-mercurous chloride electrode. It consists of glass vessel having bent side tube. Pure mercury is placed at the bottom of the tube. Which is covered with a paste of mercury-mercurous chloride, Calomel. The remaining portion of the cell is filled with a solution of normal. A platinum wire sealed into a glass tube is dipped into mercury layer is used to provide the external eletrical contact.