penny to form a more uniform electrical field which plates more evenly. In commercial installations the tanks are frequently lined with the lead anode. In contrast to many electrode processes which are very efficient, this reaction is only 25% efficient even in most optimum commercial processes. Side reactions cause vigorous bubbling which forms a dangerous carcinogenic aerosol of the chromic oxide solution. Spattering is easily observed.
Equation
CrO3 + Pb + H2O --> PbCrO4 + 2e- + 2 H+
CrO3 + 6 H+ + 6 e- --> Cr + 3 H2O
2 H+ + 2 e- --> H2
Reference
H. N. Alyea and F. B. Dutton, Eds.,"Tested Demonstrations in Chemistry", 6th ed., Journal of Chemical Education, Easton, Pennsylvania (1965) p.72,77.
MetalsFinishing 50th Guidebook Directory, Metals and Plastics Publications, Inc.,Hackensack, N.J., (1982) .