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How does bleach whiten clothes and why does it ruin clothes if to much is applied?
Answer 1:

Washing Bleach contains Hypocloric acid, which acts as a very strong oxidizer. It works by oxidizing dye agents in the stains so that they become colorless. It preferentially attacks dyes since strongly colored (or odorous) organic chemicals often have conjugated double carbon bonds. These bonds have easily moved electrons which allow selective interaction with visible light, hence they absorb some frequencies and not others, inducing color.

Bleach interacts with the organic molecules by adding chlorine or oxygen to the compound which removes the bonds or even breaks up the molecule. This serves two purposes: the color is removed or greatly reduced, and the new sites increase the water solubility of the material, so it can often be removed by washing.

Commercial dyes are rated by a 'fugitive' rating which describes how they will break down in UV or due to chemical attack. Typically, they are much more stable than typical stain dyes, so although the bleach attacks everything, they often survive. However, it is often the case that clothing vendors over-dye some cloths to create very heavily saturated colors. In such cloth, the excess dye is not really bound to the fiber, but usually to a bonding agent (called a fixative). Both the excess dye and the fixative are attacked by bleach, often with quite odd results. (I had a green shirt on which red wine was spilled. After bleaching, the red wine stain was gone, but I had a yellow/tan shirt...).

This isn't completely the fault of the cloth manufacturers. Dyes are all relatively active compounds, some of the prettiest are the most fugitive... Similar problems happen in paints watercolor is particularly troublesome) where artist colors are known to decompose in a few weeks in moderate sunlight... This is why toxic cadmium compounds are still used in artist paints, they are very stable over time. One could not use such dyes in cloth for obvious reasons.

Answer 2:

Bleach whitens clothes by a process of oxidation. The molecules that make clothes dirty are quite big. Bleach breaks up these big molecules into smaller ones that are not colored. These smaller molecules are usually washed away in the washing machines.

A good way to test how bleach works is by mixing bleach with some colors (try mixing some green leaves with bleach). Bleach ruins clothes because it also oxidizes clothes a little.

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