6Measuring the standard electrode potential of a metal
7Measuring the standard electrode potential of magnesium
8How to use electrode potentials Values and signs allow prediction of spontaneous reactionE.g. will zinc react with Cu2+ spontaneously?
9This diagram will predict the direction of spontaneous reaction given electrode potentials -Electrode potential scale – note sign+ACTULACTULCu2++2e-CuZn2++2e-ZnSpontaneous reaction
10Consider the following and reach a conclusion Cu2+ + e- CuCu2+ + 2e- CuCu+ + e- Cu
11Cu+ + Cu+ Cu + Cu2+Disproportionation – simultaneous oxidation and reduction of the same species
12Application of Electrode Potentials Give a comparison of the effectiveness of galvanising (zinc plating) and tin plating of steelIron reacts with dilute hydrochloric acid, copper does not, but copper will react with conc nitric acid
13Effect of concentration Treat cell reaction as an equilibrium system:If change supports/shifts eqm to the right then emf increases & vice versaCu2+ + Zn Zn CuIncrease [Cu2+] emf increasesIncrease [Zn2+] emf decreases
14Limitations No indication of rate of reaction. Mixtures which can react may co-exist for long periods due to very slow reaction rateE.g. H2 & O2 (thermodynamically unstable, kinetically stable)This is caused by high activation energy
16Limitations Standard electrode potentials refer to standard conditions Temp and concentrations affect electrode potentials.Reactions not predicted by electrode potentials can occur under non-standard conditionsE.g. solid K2Cr2O7 and conc HCl
17Galvanisation – sacraficial anode Construct the cell reaction for a zinc/iron cellConstruct the cell reaction for a tin/iron cellWhy fix magnesium to the hull of a battleship?