Page 20 - Curriculum Visions Dynamic Book

Sulphur dioxide as a bleaching agent
Any chemical that makes a material brighter Bread bleach
and makes stains invisible is called a bleach. Bleaches also kill bacteria.
A bleach removes stains by reacting with the stain, making it colourless. Bleaches work either by adding oxygen to or removing it from the stained material. The colourless product is
Sulphur dioxide is not a strong bleach and so can be used to bleach silk, wool and even flour (white flour for white bread). Sulphur dioxide will work on most dyes containing oxygen. In this case the sulphur dioxide acts as a reducing agent taking
often more soluble and so is also more easily oxygen from the dye and
removed by detergents.
A number of sulphur-based products are
making it colourless. But note that this process is reversible. The dye gradually picks up
used on a large scale for industrial bleaching. oxygen from the air and
becomes coloured again. This is why, for example, straw hats, that were white
Sodium peroxydisulphate is used as a domestic
bleach for use in home laundry applications
because it is safer than chlorine-based bleaches when new, gradually turn yellow
on delicate textiles. It is an example of a bleach that oxidises the staining material.
Sodium sulphite and sulphur dioxide are used as industrial bleaches, especially for wood pulp. They act in the opposite way, reducing materials by removing oxygen from them.
(the original colour of the straw containing natural dyes).
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 White bread is made with flour that has been bleached using sulphur dioxide. Some brown bread also uses bleached white flour that has subsequently been dyed.
Coloured dye + sulphurous acid (sulphur dioxide + water) react to give colourless dye + sulphuric acid
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Oxygen
Sulphur
Sodium
 In sodium peroxydisulphate two oxygen atoms are joined by a weak bond which is easily broken. Such compounds are reactive and can act as oxidising agents.
Weak bond