Electrochemistry

1. Electrochemistry Fundamentals

2. Oxidation & Reduction Oxidation of iron (II) to iron (III) by permanganate Fe2+ + MnO4- ? Fe3+ + Mn2+ Oxidation: losing electrons Reduction: gaining electrons

3. Electricity - Units Charge (q) 1 atomic charge = 1.602 X 10 -19 Coulombs q=m X F, F: Faraday Constant = 96490 Coul/mol Current (i) Amps = Coul/sec i=q/t Electrical Potential Volts = Joules/Coul V or E = IR ?G = -nFE

4. Electrochemical Cells

5. Cell Components & Cell Notation

6. Standard Electrode Potentials The electrode potential of a half cell reaction when all reactants & products exist at unit activity Written as standard reduction potentials Cu2+ + e- ? Cu E� = + 0.153 Volts Silver/silver ion 0.056M Nickel / Nickel ion 0.018MSilver/silver ion 0.056M Nickel / Nickel ion 0.018M

7. Electro-chemical Series

8. Concentration Effects � The Nernst Equation Electrode potentials measure reaction driving force This �driving force� is concentration dependent The �driving force� is quantified by the Nernst Equation:

9. The Nernst Equation

10. Old Man�s Nernst Equation

11. Problem A palladium wire in a 0.025 F hydrochloric acid solution which is saturated with hydrogen gas at a pressure of 0.50 atm and which is connected through a potassium chloride salt bridge to a cell consisting of a zinc electrode immersed in a 0.050 M zinc nitrate solution. Use line notation to sketch cell Find E�, Ecell & determine if electrolytic or galvanic

12. Problem A metallic silver electrode in 0.015 F silver nitrate is connected through a salt bridge to a 0.028 F nickel chloride solution into which a nickel electrode is immersed. Select a material for the salt bridge Use line notation to sketch cell Find E�, Ecell & determine if electrolytic or galvanic

13. Problem A platinum wire immersed in a 1F sulfuric acid solution containing 0.10 M cerium (IV) and 0.05 M cerium (III). This solution is in contact via a semipermeable membrane to a 10 F sodium hydroxide solution containing 0.05 M permanganate ion and 0.001 M manganate ion containing a gold electrode. Use line notation to sketch cell Find E�, Ecell & determine if electrolytic or galvanic

14. Standard Electrode Potentials & Equilibrium Constants Galvanic cells produce current because the net cell reaction is not at equilibrium

15. Problem Determine E� for the reduction: AgCl (s) ? Ag (s) + Cl- (aq) Ksp (AgCl) = 1.8 X 10-10

16. Qualitative Effects Pt|Fe3+ (aq), Fe2+ (aq)||H+ (aq),| H2 (g)|Pt

17. Qualitative Effects II Pt|Cr3+(aq), Cr2+(aq)||AgCl (s), Cl- (aq)|Ag

18. Cell Current Electrodes & Conductor Electrons serve as charge carriers In the bulk solution Charge movement involves migration of anions & cations Ions from salt bridge neutralize changes in charge of anode & cathode cells At the electrode surface Oxidation & reduction provide mechanism for ionic conduction in solution to couple with electron conduction of electrode

19. Structure of Solution Potential

20. Solution Structure The Double Layer

21. Faradaic versus NonFaradaic Currents Faradaic Current Direct transfer of electrons at electrode surface by oxidation or reduction Solution Current Non � Faradaic Current Current converted to energy by solution �Friction� Found in AC electrochemical systems Capacitive current increases with electrode area and frequency Electrode charging

22. Ohmic Potential or IR Drop Electrical potential required to overcome the resistance of ions to movement Follows Ohm�s law, V = IR Always subtracted from overall cell potential Ecell = Ecathode � Eanode � EIR

23. Cell Polarization Cell polarization create nonlinear relationships in current voltage curves: e.g. Ideal polarized electrode Ideal non-polarized electrode