|MadSci Network: Chemistry|
Hydrogen peroxide bleaching works by oxidizing the colour pigments.
The colours in the pigments are due to alternating single and double carbon bonds, which absorb light in the visible spectrum. When bleaches attack these pigments, the some of the double bonds are split into single bonds, which breaks up the colour-absorbing system.
In the bleach process, Hydrogen peroxide (H202) is reduced to water (H20) in the prescence of acid (H+).
H202 + 2H+ + 2e- ----> 2 H20In terms of whether a higher or lower pH is more effective, all the textbooks I consulted agree that bleaching is generally more effective in an acidic (low pH) solution (hence, the equation above).
I hope this answer has been of some assistance,
University of Technology, Sydney
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