Question
Sun February 17, 2013 By:

I would like to know about the cleansing action of soaps

Expert Reply
Sun February 17, 2013

A soap molecule has an ionic part and a non-ionic part. A soap molecule structure is like a tadpole,where its tail indicates the long chain of saturated hydrocarbons(non-ionic)part and the head indicates the ionic part(containing ions).Now, u know that dirty clothes do not get easily cleaned in water by simply rubbing it beacuse it contains some oil molecules or grease molecules which are im-miscible(cannot be mixed)in water.Now here comes the use of soap molecules...

when the soap molecules come in contact with water,the non-ionic part of the soap molecule (hydrocarbon chain)attaches itself to the dirt or the grease because it is miscible in it.The ionic part remains in the water because water is also partially ionic in nature...so you see that "like dissolves the like".these soap molecules gradually surround the dirt particle by dissolving their non-ionic end in it and gradually form michelle(a round structure around the dirt particle) and then they detach the dirt particle and incapsulate(imbed)it in water molecules,making it miscible in water.thus the cloth gets thoroughly cleaned after being rinsed nicely.. 

 

A soap molecule has an ionic part and a non-ionic part. A soap molecule structure is like a tadpole,where its tail indicates the long chain of saturated hydrocarbons(non-ionic)part and the head indicates the ionic part(containing ions).Now, u know that dirty clothes do not get easily cleaned in water by simply rubbing it beacuse it contains some oil molecules or grease molecules which are im-miscible(cannot be mixed)in water.Now here comes the use of soap molecules...

when the soap molecules come in contact with water,the non-ionic part of the soap molecule (hydrocarbon chain)attaches itself to the dirt or the grease because it is miscible in it.The ionic part remains in the water because water is also partially ionic in nature...so you see that "like dissolves the like".these soap molecules gradually surround the dirt particle by dissolving their non-ionic end in it and gradually form michelle(a round structure around the dirt particle) and then they detach the dirt particle and incapsulate(imbed)it in water molecules,making it miscible in water.thus the cloth gets thoroughly cleaned after being rinsed nicely..

 

The cleaning action of soap occurs when oil and grease are absorbed into the hydrophobic centers of soap micelles and are washed away.

  

 

fig 7.10 - Cleansing action of soap

Sodium lauryl sulphate is a synthetic detergent present in laundry soaps, toothpastes and shampoos. The formula of sodium lauryl sulphate is CH 3 (CH 2 1 1 SO 4 - Na + . It has a hydrophilic sulphate group and a hydrophobic dodecyl (C 1 2 H 2 5 ) group. These detergent molecules are called 'anionics ' because they have negative charge at the hydrophilic end. There are detergents which are 'cationics ' that is they have positive charge at the hydrophilic end.

Ask the Expert