Advantages of syntbetic detergents over soaps
1 . Synthetic detergents can be used even in case of hard water whereas soaps fail to do so .
2 . Synthetic detergents can be used in the acidic medium while soaps cannot because of their hydrolysis to free acids .
3 . Synthetic detergents are more soluble in water and hence , form better lather than soaps .
4 . Synthetic detergents have a stronger cleansing action than soaps .
Chemistry in Colouring Matter
The natural or synthetic colouring matter which are used in solution to stain materials especially fabrics are called dyes .
All colouring substances are not dyes , e . g ., azobenzene , a coloured substance does „ not act as dye . A dye have following characteristics :
1 . It must have a suitable colour . 2 . It can be fixed on the fabric either directly or with the help of mordant .
3 . It must be resistant to the action of water , acid and alkalies . The groups , responsible for colour , are called chromophore , e . g .,
Classification of Dyes on the Basis of Constitution
( i ) Nitro or nitroso dye Chromophore NO2 or NO group , Auxochrome = -OH group , e . g ., picric acid , martius yellow , Gambine , naphthol yellow-S .
( ii ) Azo dye , e . g ., bismark brown , methyl orange , methyl red , congo red , etc . ( iii ) Anthraquinone dye e . g ., alizarin
( iv ) Indigo is the oldest known dye . Other examples are tyrian purple , indigosol .