B26 Vanadium Oxidation States and Redox Potentials

Description
A vanadium(II) solution, which was prepared by reducing vanadate with zinc amalgam, is titrated with a cerium(IV) solution all the way to the vanadate oxidation state. Distinct color changes are observed for each of the intermediate oxidation steps. Potentiometric data is also shown.

Equation
(lavender) V2+ + Ce4+ --> Ce3+ + V3+ (blue)

V3+ + Ce4+ + H2O --> VO2+ (aqua) + Ce3+ + 2 H+

VO2+ + Ce4+ + 2 H2O --> VO3- (yellow) + Ce3+ + 4 H+

Reference
L. R. Summerlin and J. L. Ealy,Jr.,"Chemical Demonstrations A Sourcebook for Teachers", American Chemical Society, Washington, DC, (1985) p.105.