Surface Finishing - The Hong Kong Polytechnic University

Surface FinishingWhere E: The electrode potential at 25 °CE 0 :Standard electrode potential of a metal in equilibrium witha solution of its ions at unit molar activity at 25 °C= molar concentration of the ions multiple activitycoefficient.The molar activity is correspondent with the molarconcentration in vary dilute solutions.R: gas constant=8.315 J/ °C mol -1 (1 cal = 4.184 J)T: absolute temperatureZ: valency of metala: the activity of the metal iron in the solution= a M /a Mn+ , At 25 0 cF: the faraday=96486 CoulombAssuming that the metal electrode is in a standard thermodynamic state (a M = 1)E= E° + 0.059/z log 10 a Mn +Change of concentration will be the prime factor affecting the electrodepotentialAssuming that activity and concentration are equivalent, we may see thatdiluting a solution shifts the electrode potential to more negative (base) valueConcentration 1M 10 -2 M 10 -7 M 10 -20 MPotential (volts) E= E° E°-0.059 E°-0.21 E°-0.59Equilibrium M/M n+ E 0 Equilibrium M/M n+ E°Cu 2+ + 2e Cu +0.34 Ni 2+ + 2e Ni -0.25H + +e1/2H 2 0.00 Cr 3+ + 3e Cr -0.71Zn 2+ + 2e Zn -0.76 Au + + e Au +1.5Page 10IC Professional Training