1. Sodium dodecyl sulfate (SDS) {also known as sodium laurel sulfate}is an amphiphilic surfactant with applications including cleaning and disinfection, protein denaturation and cell lysing for DNA extraction. SDS forms a variety of self-assembled structures under different conditions of temperature, SDS concentration and salt concentration of the aqueous solution.

1a. (7 points) In solution, SDS behaves as anionic amphiphile. Its chemical formula is +[3(2)113] . Explain what happens when you put a molecule of SDS into aqueous solution.

Draw a chemical line structure of the SDS anion [3(2)113] . Show all the atoms (C, S, O and H) in your structure. The bond lengths in SDS are: C-H ~1.01 , C-C ~1.54, C-O ~ 1.43 , and O-S ~ 1.49. Using the fact that the non-hydrogen atoms have tetrahedral geometry, estimate the length (L) of an SDS anion in . What is L in nm?

1b. In deionized water at 300K, with [SDS] ~ 20 mM, the SDS anions form spherical micelles. Assume that the radius of the micelle is 20 (this is slightly longer than the L you calculated in 1a. - so the atoms from different molecules do not overlap at the center of the micelle). Estimate the volume of a micelle in 3 (Armstrong cubed)

1c. The molar mass of each methylene unit "CH2 " is approximately 14 g/mol. Calculate the molar mass (in g/mol) of the SDS anion. What is the mass of a single SDS anion in g? 20 4

1d. Under the conditions specified in 1b., the density of a SDS micelle is about 0.75 g/3 . The average number of amphiphiles per micelle () is referred to as the aggregation number. Use the fact that = , and your answers to part 1b. and 1c. to estimate for spherical SDS micelles.