21. When a small amount of the detergent sodium dodecyl sulfate (SDS; NaCH3(CH2)

Question

21. When a small amount of the detergent sodium dodecyl sulfate (SDS; NaCH3(CH2)OSO) is dissolved in water, the detergent ions enter the solution as monomeric species. As more detergent is added, a concentration is reached (the critical micelle concentration) at which the monomers associate to form micelles. The critical micelle concentration of SDS is 8.2 mM. The micelles have an average particle weight (the sum of the molecular weights of the constituent monomers) of 18,000. Calculate the number of detergent molecules in the average micelle.

Explanation / Answer

The molecular weight of sodium dodecyl sulfate is 288. The average micelle particle weight is 18000. Therefore the number of detergent molecules in the average Micelle is 18000/288 = 63 SDS molecule per micelle

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