Pre-Assignment

1. How will the micelle structure in nonpolar solvent be different from that in water?
2. How CMC value will be affected if an additive is used that decreases the dielectric constant of water?
3. Can one determine the CMC of a nonionic surfactant by conductivity measurement method?
4. What kind of current (d.c. vs. a.c.) is used in conductivity measurement?
5. CMCs of ionic surfactants are generally higher than the nonionic surfactants whereas aggregation numbers of ionic surfactants are generally smaller than the nonionic surfactants. Why?

Post-Assignment

1. What is the CMC of SDS?
2. Why the slopes of two straight lines above and below the CMC vary?
3. Why do we need to know the cell constant of the conductivity cell?
4. Under which condition the measured conductance of the solution is the same as the specific conductance?
5. The plot of K vs. surfactant concentration gives two straight lines with different slopes below and above the CMC. Which straight line has a smaller slope and why?
6. Using your experimentally determined CMC value and assuming a mean aggregation number of 80 for SDS micelles, estimate the micelle concentration, [micelle] for a bulk surfactant concentration of 0.080 M.
7. What is value of the CMC expressed as a mole fraction (X_CMC)? (Hint: X_CMC= (no. of mol of SDS at CMC)/( no. of mol of SDS at CMC + no. of mol of solvent)
8. Calculate the standard free energy change of micellisation, ΔG_mic?