A15 Reduction and Oxidation of Pigments in a Rose

Description
Products from the burning of sulfur in oxygen, A14, bleach a red rose. The bleached rose is inserted into the gases which are in equilibrium with a small amount of concentrated nitric acid. Red color is restored to the rose, but a distinct change in color is still observed.

Equation
SO2 + red rose pigment --> SO42- + reduced pigment (white)

reduced pigment + NO2 --> NO + oxidized pigment (red)

Reference
H. N. Alyea and F. B. Dutton, Eds.,"Tested Demonstrations in Chemistry", 6th ed., Journal of Chemical Education, Easton, Pennsylvania (1965) p.42.

L. R. Summerlin, C. L. Borgford, and J. B. Ealy,"Chemical Demonstrations A Sourcebook for Teachers",Vol. 2, American Chemical Society, Washington, DC, (1987) p.165.