Presentation on theme: "02 REDOX EQM Electrode Potential C. Y. Yeung (CHW, 2009)p.01 MetalMetal Ions Eqm between Metal & Metal Ions in a Half Cell: M n+ M Electrode [M(s)] Electrolyte."— Presentation transcript:
02 REDOX EQM Electrode Potential C. Y. Yeung (CHW, 2009)p.01 MetalMetal Ions Eqm between Metal & Metal Ions in a Half Cell: M n+ M Electrode [M(s)] Electrolyte [M n+ (aq)] Metal - Metal Ions System M n+ (aq)+ ne - M(s) Reduction Potential / Electrode Potential (E) (unit: V)
p.02 Greater tendency to reduce, larger reduction potential. M n+ (aq)+ ne - M(s) Example:E Mg 2+ | Mg = –2.38 V Mg 2+ (aq) + 2e - Mg(s) -ve reduction potential lower tendency to accept e - (FW) BW Rxn is more favorable Mg(s) tends to release e - (i.e. oxidation). i.e. Mg is a reactive metal. measured under standard conditions (p. 203) (Standard Reduction Potential)
cell e.m.f. p.03Example:E Mg 2+ | Mg = –2.38 V E Cu 2+ | Cu = V BW rxn favoured: Mg is a good R.A. FW rxn favoured: Cu 2+ is a good O.A. Therefore: Mg(s) Mg 2+ (aq) + 2e - Cu 2+ (aq) + 2e - Cu(s) +2.38V+0.34V +) Cu 2+ (aq) + Mg(s) Cu(s) + Mg 2+ (aq) E cell = +2.72V E Mg 2+ | Mg = –2.38 V E Cu 2+ | Cu = V oxidation takes place [Anode] reduction takes place [Cathode] Cell e.m.f. = E cathode – E anode
p.04 Mg(s) | Mg 2+ (aq) Cu 2+ (aq) | Cu(s) Cell Diagram ~ presenting an electrochemical cell … anodecathode salt bridge phase boundary Zn(s) | Zn 2+ (aq) Ag + (aq) | Ag(s) E cell = ? V Check p.207 E Zn 2+ | Zn = –0.76 V E Ag + | Ag = V AnodeCathode E cell = – (-0.76) = +1.56V oxidation reduction electrode of anode electrode of cathode
p.05Summary: More –ve reduction potential (E), less likely to be reduced, oxidation is more favourable. i.e. stronger reducing power. More +ve reduction potential (E), more likely to be reduced, reduction is more favourable. i.e. stronger oxidizing power. Electrochemical Series (E.C.S.) could be obtained by arranging the standard electrode potentials.
p.06Assignment p.212 Check Point 20.5(a) [due date: 7/5 (Thur)] Next …. Other Common Types of Half Cells, Standard Hydrogen Electrode (S.H.E.), Measurement of Standard Electrode Potentials (p ) Past Paper Q.1-2 [K sp ] [due date: 7/5 (Thur)]