Colloidal electrolytes Soaps and detergents

The formation of micelles results in a sharp drop in the electrical conductivity per mole of the electrolyte. Suppose 100 sodium and 100 stearate ions were present individually. If the stearate ions aggregate into a micelle and the micelle binds 70 Na as counter ions, then there will be 30 Na ions and 1 micellar ion having a charge of —30 units a total of 31 ions. The same quantity of sodium stearate would produce 200 ions as individuals but only 31 ions if the micelle is formed. This reduction in the number of ions sharply reduces the conductivity. The formation of micelles also reduces the osmotic pressure of the solution. The average molar mass, and thus an estimate of the average number of stearate ions in the micelle, can be obtained from the osmotic pressure. 

By incorporating molecules of hydrocarbon into the hydrocarbon interior of the micelle, the soap solution can act as a solvent for hydrocarbons. The action of soap as a cleanser depends in part on this ability to hold grease in suspension. 

The detergents are similar in structure to the soaps. The typical anionic detergent is an alkyl sulfonate, ROSO Na. For good detergent action, R should have at least 16 carbon atoms. Cationic detergents are often quaternary ammonium salts, in which one alkyl group is a long chain (CH3)3RN C1 is a typical example if R has between 12 and 18 carbon atoms. 

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