what are micelles? why does it form when soap is added to water? will a micelle be formed in other solvents such as ehanol also ? state briefly how the formation of micelles help to clean the clothes having oily spots.

Asked by adarshku34567 | 15th Jan, 2018, 10:01: AM

Expert Answer:

1) MicellesA micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre.
2) When soap is dissolved in water, its hydrophobic ends attach themselves to dirt and remove it from the cloth, 

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.

3) Organic compounds like ethanol would not be able to interact with micelle when present in small amounts.  The energy requirement for bringing the hydrophobic tail into solution may decrease, leading to an increase in micelle concentration. Conversely, adding alcohol will result in a reduction in the dielectric constant of the solvent mixture thus affecting the decrease in the critical micelle concentration of ionic surfactants as a result of their lower solubility and reduced repulsion between adjacent head groups at the micelle surface. This will, in turn, make alkyl group of soap micelle soluble as they will not able to form chains. Thus, micelle formation doesn't take place in ethanol.

4)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(around structure around the dirt particle) and then they detach the dirt particle and encapsulate(embed)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 centres of soap micelles and are washed away.



Cleansing action of soap

Sodium lauryl sulphate is a synthetic detergent present in laundry soaps, toothpaste and shampoos. The formula of sodium lauryl sulphate is CH3(CH2)11SO4- Na+. It has a hydrophilic sulphate group and a hydrophobic dodecyl (C12H25) group. These detergent molecules are called 'anionics ' because they have a negative charge at the hydrophilic end. There are detergents which are 'cationic ' that is they have the positive charge at the hydrophilic end.

Answered by Ramandeep | 15th Jan, 2018, 12:29: PM