GTBL042-16 GTBL042-Callister-v2 September 13, 2007 13:10
Revised Pages666 • Chapter 16 / Corrosion and Degradation of MaterialsVoltmeterMembraneH+ solution,
1.0 MPtVHydrogen gas, 1 atm pressureFigure 16.4 The standard
hydrogen reference half-cell.itself does not take part in the electrochemical reaction; it acts only as a surface
on which hydrogen atoms may be oxidized or hydrogen ions may be reduced. The
electromotive force electromotive force (emf) series(Table 16.1) is generated by coupling to the standard
(emf) series hydrogen electrode standard half-cells for various metals and ranking them according
to measured voltage. Table 16.1 represents the corrosion tendencies for the several
metals; those at the top (i.e., gold and platinum) are noble, or chemically inert. Moving
down the table, the metals become increasingly more active, that is, more susceptible
to oxidation. Sodium and potassium have the highest reactivities.Table 16.1 The Standard emf SeriesStandard Electrode
Electrode Reaction Potential, V^0 (V)
Au^3 ++ 3 e−→Au +1.420
O 2 +4H++ 4 e−→2H 2 O +1.229
Pt^2 ++ 2 e−→Pt ∼+1.2
Ag++e−→Ag +0.800
Increasingly inert Fe^3 ++e−→Fe^2 + +0.771
(cathodic) O 2 +2H 2 O+ 4 e−→4(OH−) +0.401
Cu^2 ++ 2 e−→Cu +0.340
2H++ 2 e−→H 2 0.000
Pb^2 ++ 2 e−→Pb −0.126
Sn^2 ++ 2 e−→Sn −0.136
Ni^2 ++ 2 e−→Ni −0.250
Co^2 ++ 2 e−→Co −0.277
Cd^2 ++ 2 e−→Cd −0.403
Fe^2 ++ 2 e−→Fe −0.440
Increasingly active Cr^3 ++ 3 e−→Cr −0.744
(anodic) Zn^2 ++ 2 e−→Zn −0.763
Al^3 ++ 3 e−→Al −1.662
Mg^2 ++ 2 e−→Mg −2.363
Na++e−→Na −2.714
K++e−→K −2.924