Page 15 - Curriculum Visions Dynamic Book

Demonstrating the bleaching action of chlorine
The bleaching action of chlorine gas can be seen by bubbling chlorine through a solution containing the vegetable dye litmus, an indicator. The sequence of pictures shows the progressively lighter colour of the solution.
bleach: a substance that removes stains from materials either by oxidising or reducing the staining compound.
indicator: a substance or mixture of substances that change colour with acidity or alkalinity.
oxidising agent: a substance that removes electrons from another substance (and therefore is itself reduced).
reducing agent: a substance that gives electrons to another substance.
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 Chlorine gas is produced by reacting hydrochloric acid and potassium manganate.
How bleach works
A coloured natural material gets its colour from the way that certain combinations of carbon atoms are linked together by double bonds. Synthetic dyes are mainly also based on carbon compounds.
The colouring chemicals are able to absorb some forms of light rays while reflecting others. When a bleach reacts with the natural material, the bleach breaks up the bonds, forming new substances that are not able to absorb light and so are colourless.
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Oxygen
Carbon
Hydrogen
  The solution gradually clears as the dye is bleached.
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  Chlorine is bubbled through the gas jar containing litmus dye.
Colour in this solution is due to the two bonds here. The oxidising effect of chlorine breaks these bonds and bleaches the solution.
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