Ele ctrode potential, electrochemical series

ELECTRODE POTENTIAL, STANDARD ELECTRODE POTENTIAL, SHE, ELECTROCHEMICAL SERIES

1. Dr. K. RAJENDER REDDY LECTURER IN CHEMISTRY Email:[email protected] Wednesday, April 22, 2020 1 ELECTRO CHEMISTRY- KRR

2. Electrochemistry ( Electrode Potential, Electro chemical series ) Wednesday, April 22, 2020 2 ELECTRO CHEMISTRY- KRR

3. Electrode potential The tendency of a metal to lose the electrons (oxidation) or gain the electrons (reduction), when it is in contact with solution of its own salt is called electrode potential .   When a metal [M] is placed in a solution containing its own ions [ M n + ], then the metal may undergo either oxidation or reduction. If the metal undergoes oxidation, then the positive metal ions may pass into the solution   M M n + + ne ‒   If the metal undergoes reduction, then the negative ions may get deposited over the metal.   M n + + ne ‒ M Wednesday, April 22, 2020 3 ELECTRO CHEMISTRY- KRR

4. Zn in ZnSO 4 When Zn is placed in a solution of its own salt, zinc undergoes oxidation with the release of electrons. The electrons liberated in the process, accumulate over the surface of the metal and hence, the metal is negatively charged. Now, the negatively charged metal attracts the positive ions from the solution, and hence formation of a double layer takes place near the surface of the metal. Wednesday, April 22, 2020 4 ELECTRO CHEMISTRY- KRR

5. Cu in CuSO 4 When Cu is placed in the solution of CuSO 4 , the copper ions in the solution gets deposited over the metal and hence the metal becomes positively charged. The positively charged metal attracts the negatively charged sulphate ions in the solution and hence a doubly charged layer is formed near the metal. Wednesday, April 22, 2020 5 ELECTRO CHEMISTRY- KRR

6. Standard Electrode Potential Standard Electrode Potential : The potential of an electrode at 25 o C with 1 M concentration of electrolyte is called standard electrode potential (E ). Oxidation potential = - Reduction potential Wednesday, April 22, 2020 6 ELECTRO CHEMISTRY- KRR

7. MEASURING OF ELECTRODE POTENTIAL It is not possible to determine experimentally the potential of a single electrode, We can only measure the potential difference between two electrodes potentiometrically . In order to measure the electrode potential, NHE is taken as primary reference electrode Wednesday, April 22, 2020 7 ELECTRO CHEMISTRY- KRR

8. Standard hydrogen electrode(SHE) It contains 1 M HCl in a vessel In which Pt plate is partially dipped act as conductor hydrogen gas at 1 atm pressure bubbled into the solution at 25 o C. The potential Of NHE arbitrarily taken as zero, It is represented as Pt, H 2 (1 atm )/ H + Wednesday, April 22, 2020 8 ELECTRO CHEMISTRY- KRR

9. Electrochemical Series Electrochemical Series : The arrangement of electrodes in the increasing order of their standard reduction potentials is called electrochemical series. In this top electrode is Li and the bottom electrode is Fluorine Wednesday, April 22, 2020 9 ELECTRO CHEMISTRY- KRR

10. Significance of electro chemical series The metal which is higher in electrochemical series acts as reducing agent or anode and undergoes corrosion first. Metals above hydrogen are called active metals, which can displace hydrogen from dilute acids or water. The metals below hydrogen are less reactive . They do not liberate Hydrogen from dilute acids or water Wednesday, April 22, 2020 10 ELECTRO CHEMISTRY- KRR

11. Significance of electro chemical series The metal with higher negative potential displace a metal with lower negative potential or positive potential from the salt solution of metal. The reactivity or reducing character decreases From top to bottom, So Li is the strongest reducing agent and fluorine is the strongest oxidizing agent. Wednesday, April 22, 2020 11 ELECTRO CHEMISTRY- KRR

12. E lectro chemical series Wednesday, April 22, 2020 12 ELECTRO CHEMISTRY- KRR

13. THANK U Wednesday, April 22, 2020 13 ELECTRO CHEMISTRY- KRR