Question

Critical micelle concentration(CMC) of soap solution lies in the range of:
A.${{10}^{-6}}-{{10}^{-5}}M$
B.${{10}^{-5}}-{{10}^{-4}}M$
C.${{10}^{-3}}-{{10}^{-2}}M$
D.${{10}^{-4}}-{{10}^{-3}}M$

Answer 1

Hint: Micelle formation can take place when the threshold for the temperature and the concentration is broken. For soaps, micelle formation is a necessary step for the cleansing action.

Complete answer:
In order to answer our question, we need to learn about soap and soap solutions. Soaps that are used in cleaning products are generally potassium or sodium salts of long chain fatty acids eg. stearic, oleic and palmitic acids. By heating fat, sodium soaps are formed (Le glyceryl ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is known as saponification. In this reaction, soap obtained remains in colloidal form; esters of fatty acids are hydrolysed. It is precipitated from solution by adding sodium chloride. The solution left after removing so contains glycerol and can be recovered by fractional distillation. Both sodium and potassium soaps are soluble in water and can be used for cleaning purposes. Generally potassium soaps are softer to the skin than sodium soap. These can be prepared by taking KOH in place of NaOH in the above reaction.
Now, let us come to the question. Soap molecules contain micelles which help in the cleansing action. Kraft temperature is the temperature in which formation of micelles takes place, and the concentration also has a barrier. This concentration barrier is called “ Critical Micelle Concentration” and for soaps the CMC lies in the range of ${{10}^{-4}}-{{10}^{-3}}M$.

So, we get option D as the correct answer for the question.

Note:
The property of micelles is that they act as electrolytes in low concentration, and when concentration is high, they behave as colloids.