6. The following table shows the experimental surface tension data for an aqueous solution of nonylphenyl ethoxylate NPE15 at 20C (the subscript 15 indicates that we have 15 oxyethylene groups): cx 10"/moll y/mNm? 0.4 0.8 57.5 42.0 1.2 28.0 1.3 33.0 1.6 33.5 2.0 33.5 (a) Provide an estimate of the critical micelle concentration (cmc) as well as the adsorption, T, and area occupied by each adsorbed surfactant molecule at a concentration equal to 0.2 x 10moll? (b) Explain the minimum in the surface tension versus concentration plot. 7. At 20C the surface tension of water and n-octane are 72.8 and 21.8 mNm-, respectively, and the interfacial tension of the n-octane-water interface is 50.8 mNm 1. Will n-octane spread on water? What will happen if a drop of water is placed on the n-octane-air surface? 8. (a) The initial spreading coefficient, SB/A is reported to be 36.0 m Nm' for n-heptanol on water at 20C. The surface tensions of n-heptanol, yo, and water, ya at 20C are 26.0 mNm- and 72.8 mNm , respectively. Calculate the interfacial tension of n-heptanol and water, YAB. (b) At 20C, the surface tension of oleic acid, ye, is 32.5 mNm and the interfacial tension of oleic acid and water, YAB, is 15.5 mNm + Solely based on this data and in (a) above, which liquid between oleic acid and n-heptanol would you recommend for evaporation control? Show clearly your reasoning