Sun February 17, 2013 By: Yogiraj Karambelkar

1) why does micelle formation takes place when soap is added to water? Why are micelles not formed when soap is added to ethanol? 2) State any 4 characteristics of isomers.

Expert Reply
Sun February 17, 2013

1) Micelle formation takes place when soap is added to water. This is because, Soap is made up of two parts, i) hydrophilic part, which is water loving and ii) hydrophobic part, water repelling part. A soap molecule has a long chain of an alkyl group, which is hydrophobic and –SO4- Na+, which is hydrophilic. Since SO4- Nais the acid head of the soap and is capable of ionic reactions, it dissolves in water whereas the carbon chain dissolves in oil.

When soap is added to water, the soap molecules align themselves in a spherical fashion as ionic ends face away from each other due to the repulsive forces of the negative charge while the hydrophobic part of the soap is faced inside away from water. This spherical formation by soap in water is called micelle formation.

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.

3) Characteristics of isomers:-

a) They have same molecular formula but different structural formula.

b) They show similar properties only when they contain same functional group.

c) Two isomers can have different boiling points. For example in isomers of pentane branched chain pentane will have less boiling point than linear because boiling point depends on the surface area which is more in case of n-pentane (linear).

d) Isomers can have different functional groups. For example aldehyde and ketone are two isomers but they contain different functional groups.

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