Experiment (10):Determination of Critical Micelle Concentration (CMC) Theory Surfactants, sometimes called Surface active substances (SAS) are amphiphilic materials containing both a non polar long- chain hydrocarbon “tail” and polar, usually ionic, “head” groups. Fig. (10.1) : Spherical micelle of sodium dodecyl sulfate

  Types of Surfactants:  Depending on the chemical structure of the surfactants can be classified into four types: 1-Cationic: Dodecylamine hydrochloride, Hexadecyltrimethyl ammonium bromide, 2-Anionic: Sodium stearate, sodium dodecyl benzene sulphonate, … 3-Ampholitic (Zwitteriionic): Dodecyl betaine 4-Non ionic: Tweens, Triton X-100

Critical micelle concentration, (CMC): The concentration (actually an arbitrary concentration within a narrow range) above which micelles form. Experimentally, the CMC is found by plotting a graph of a suitable physical property as a function of surfactant concentration. An abrupt change of slope marks the CMC.

Object To determine CMC of SDS by conductivity Procedure 1-Prepare a stock solution of 0.02 M of SDS of volume 50 mL of the surfactant (given by the instructor). 2- From the stock solution, prepare the following a series of dilute solutions: (50 ml each) 0.005 , 0.008, 0.01, 0.015, M 3-By using the conductivity meter, measure the specific conductivity (K) in S cm-1.