Chapter 7 Electrochemistry §7.9 Electrode potential and electromotive forces H2O O2 H2 pH  / V 2 4 6 8 10 12 14 0.401 -0.828 0.000 1.229

7.9.1. Influential factors for electrode potential 1) emf’s and G of reaction in different forms Exercise: Compare G1, G2, G3 and E1, E2, E3. reaction: H2 + Cu2+  Cu + 2H+ G1, E1 1/2 H2 + 1/2 Cu2+  1/2 Cu + H+ G2, E2 Cu + 2H+  H2 + Cu2+ G3, E3

Give the relationship between  2)  of electric couple between different oxidation state Give the relationship between  Fe3+ Fe2+ Fe Exercise

3)  of different electrode AgCl = Ag+ + Cl- Ag(s)|AgNO3(c1) ||KCl(c2) |AgCl(s)|Ag(s) Exercise: deduce the relationship between and

Nernst equation 7.9.2. Concentration-dependence of  for Ag+/Ag electrode (Ag+/Ag) depends on [Ag+] , or (Ag+/Ag) responds to [Ag+]. The relationship between (Ag+/Ag) and [Ag+] can be used for quantitative electroanalysis of Ag+.

Can we use hydrogen electrode for measuring the pH of the solution? Give the principle of the measurement.

7.9.3. pH-dependence of  : Pourbaix diagram For electrode reaction with H+ or OH- participating in, the electrode potential will depend on pH. 2H+ + 2e-  H2 H2O O2 H2 pH  / V 2 4 6 8 10 12 14 0.401 -0.828 0.000 1.229  = ⊖ + 0.05916 lgaH+ = 0.000 - 0.05916 pH O2 + 4H+ + 4e-  2H2O  = ⊖ + 0.05916 lgaH+ = 1.229 - 0.05916 pH pH-potential diagram/Pourbaix diagram

Application of Pourbaix diagram Cu2+ Cu(OH)2 Cu pH  / V 2 4 6 8 10 12 14 CuO22 Cu2O

Pourbaix diagram of iron-water system Equilibrium line Fe2+ Fe2O3 Fe pH  / V 2 4 6 8 10 12 14 Fe3O4 Fe3+ FeO22 Stable zone Stable state Product Reaction Protection, passivation, active dissolution, electroplating, electrosynthesis