UCSB Science Line How does bleach whiten clothes and why does it ruin clothes if to much is applied? Answer 1:Washing Bleach contains Hypocloric acid,whichacts as a very strong oxidizer. It works byoxidizing dye agents in the stains so that theybecome colorless. It preferentially attacks dyessince strongly colored (or odorous) organicchemicals often have conjugated double carbonbonds. These bonds have easily moved electronswhich allow selective interaction with visiblelight, hence they absorb some frequencies and notothers, inducing color. Bleach interacts withthe organic molecules by adding chlorine or oxygento the compound which removes the bonds or evenbreaks up the molecule. This serves two purposes:the color is removed or greatly reduced, and thenew sites increase the water solubility of thematerial, so it can often be removed bywashing.Commercial dyes are rated by a'fugitive' rating which describes how they willbreak down in UV or due to chemical attack.Typically, they are much more stable than typicalstain dyes, so although the bleach attackseverything, they often survive. However, it isoften the case that clothing vendors over-dye somecloths to create very heavily saturated colors. Insuch cloth, the excess dye is not really bound tothe fiber, but usually to a bonding agent (calleda fixative). Both the excess dye and thefixative are attacked by bleach, often with quiteodd results. (I had a green shirt on which redwine was spilled. After bleaching, the red winestain was gone, but I had a yellow/tan shirt...).This isn't completely the fault of the clothmanufacturers. Dyes are all relatively activecompounds, some of the prettiest are the mostfugitive... Similar problems happen in paintswatercolor is particularly troublesome) whereartist colors are known to decompose in a fewweeks in moderate sunlight... This is whytoxic cadmium compounds are still used in artistpaints, they are very stable over time. One couldnot use such dyes in cloth for obvious reasons.Answer 2:Bleach whitens clothes by a process ofoxidation.The molecules that make clothes dirty are quitebig. Bleach breaks up these big molecules intosmaller ones that are not colored. These smallermolecules are usually washed away in the washingmachines. A good way to test how bleach worksis by mixing bleach with some colors (try mixingsome green leaves with bleach). Bleach ruinsclothes because it also oxidizes clothes a little.Click Here to return to the search form. Copyright © 2015 The Regents of the University of California, All Rights Reserved.UCSB Terms of Use
