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Explain the cleansing action of soap.

Asked by Adeeba Riyaz(student) , on 13/12/13


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 We know that soaps and detergents make oil and dirt present in a cloth dissolve in water, thereby making the cloth clean.

Soap has one polar end (the end with sodium or potassium ion) and one non-polar end (the end with fatty acid chain) as shown in the figure. The polar end is hydrophilic in nature i.e., this end is attracted towards water. The non-polar end is hydrophobic, but lipophilic in nature i.e., it is attracted towards hydrocarbons, but not attracted towards water.

 

   A soap molecule

When soap is dissolved in water, its hydrophobic ends attach themselves to dirt and remove it from the cloth, as shown sequentially in the figure that follows.

   


 Diagram representing the cleansing action of soap

 

First, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in water like particles in a colloidal solution. The various micelles present in water do not come together to form a precipitate as each micelle repels the other because of the ion-ion repulsion.

Thus, the dust particles remain trapped in micelles (which remain suspended) and are easily rinsed away with water. Hence, soap micelles remove dirt by dissolving it in water.

Hope this helps.

Posted by Anushka(student)on 5/3/13

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More Answers

soap form structure called miclles which has a hydrophobic end and a hydrophylic end .

hydrophobic end consits of carbon chain which is dissolved in dirt and other hydrophylic end consits of Na+ ion dissolves in water ,many such structures get surround to dirt particle and when the cloth is agitated in water the dirt is seperated with soap.  

Posted by Kanishk Ameta(student)on 5/3/13

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.


Posted by Devi(student)on 5/3/13

 Hope this helped you!!!!!

Posted by Devi(student)on 5/3/13

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.

cleansing action of soap

 

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.

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Posted by Ashi Jain(student)on 5/3/13

Hi,

 

Esters react in the presence of an acid or a base to give back alcohol and carboxylic acid as follows:

This reaction is used in the preparation of soaps and is known as saponification reaction.

Soap has one polar end (the end with sodium or potassium ion) and one non-polar end (the end with fatty acid chain) as shown in the figure. The polar end is hydrophilic in nature i.e., this end is attracted towards water . T he non-polar end is hydrophobic, but lipophilic in nature i.e., it is attracted towards hydrocarbons, but not towards water.

A soap molecule

When soap molecules are present in water, the molecules arrange themselves in the form of a cluster in such a manner that their hydrophobic ends are away from the water molecules and their hydrophilic or ionic ends are towards the water molecules (as shown in the following figure). This is known as micelle formation and the cluster that is formed is called a micelle.

 

Hope this helps.

All the Best.

Posted by Ashi Jain(student)on 5/3/13

Saponification is the process of making soap. It is defined as the reaction of an ester with a metallic base and water, i.e. the making of soap. Gray scum or gray dust is deposited on or inside the surface of a subgrade wall or floor as a result of moisture moving through the concrete and washing certain chemicals from the concrete mass. Saponification is the reaction between fats and oils with KOH or NaOH to produce soap. It is a chemical decay of a paint 's binder by alkali and moisture from a substrate. The substrate may be new concrete or fresh plaster. Saponified paint may lose its adhesion, deteriorate and get discoloured. It is a combination of lye, fats, oil and water that produces soap. Saponification is the process of converting fat into soap by treating it with an alkali. It is the alkaline hydrolysis of fat or oil to make soap.

Posted by Ashi Jain(student)on 5/3/13

  • Most dirt is non-polar. Grease consists mostly of long chain, non-polar hydrocarbons. However, water is polar, so it will not dissolve this non-polar dirt and grease.
  • When soap dissolves in water, the ions making up the soap dissociate:

RCOONa+ (s)  right arrow   RCOO(aq)  +  Na+ (aq)

The negative fatty acid ion is a surfactant (surface acting agent). The positive ion plays no part in cleaning.

  • Surfactants lower the surface tension of water, by disrupting hydrogen bonds between water molecules, and thus increase its ability to wet a surface.

Grease spot with small amount of water around it

Water does not wet grease very well.

Grease spot with water containing surfactants completely surrounding it

Water with surfactants spreads out over the grease, wetting it.

  •  
  • The fatty acid anions (surfactants) in soaps have a long, non-polar tail, consisting of a hydrocarbon chain, and a polar, anionic (negatively charged) head.

Surfactant showing polar head and non-polar tail

The non-polar tail is hydrophobic, which means that it prefers to be away from water. The polar head is hydrophilic, which means that it is attracted to water.

  •  
  • When surfactants are added to water, they do not spread evenly through the water, instead they clump together, with the negative heads pointing outwards. The negative ends interact with polar water molecules and the whole clump stays suspended in the water, forming an emulsion rather than a solution.

Surfactants clumped together

Surfactants clump together and stay suspended in water.

Non-polar grease molecule taken into the non-polar centre of the clump of surfactants




Non-polar grease molecules are taken into the non-polar centre of the clump.

  •  
  • Surfactants help to remove the dirt.

Surfactants dissolving greasy dirt and drawing water onto the dirt and fabric

The tails dissolve in the greasy dirt and the heads dissolve in water, drawing water onto the dirt and fabric.

As the water is swirled around it pulls the grease out of the fabric.

  •  
  • Surfactants keep the grease suspended in the water.

Surfactants suspending grease in water

Keeping the grease suspended means it can be carried away by the water.

Soap, water and grease together form an emulsion, with the soap acting as an emulsifier, suspending the normally incompatible

Posted by Ashi Jain(student)on 5/3/13

Cleansing action of soap:

When soap is at the surface of water, the ionic end of soap orients itself towards water and the hydrocarbon tail orients itself aligns itself along the dirt. Thus, clusters of molecules are formed in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of the micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Now, when water is agitated, the dirt suspended in the micelles is also easily rinsed away.

Posted by Vishesh Chauras...(student)on 23/10/13

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Posted by Darshil Shah(student)on 9/12/13

Mechanism of cleansing action of soap:

I. Soap gets dissolved in water.

ii. The non-polar ends get directed towards the centre and the polar ends get directed outwards.

iii. A cluster comprising of this arrangement is formed which is known as micelle.

iv. Dirty cloth is put in soap solution.

v. Non-polar end gets attached to the oil or dirt present in the cloth and polar end remain attached to water.

vi. Dirty cloth is agitated in soap solution.

vii. Oily and greasy particles entrapped in soap micelle gets dispersed in water.

vii. Soap water gets dirty and the cloth gets cleaned.

Posted by Gayathri Krishn...(student)on 13/12/13

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