Answer Happy

Question 1 60 55 50 45 40 C12 C14 C16 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 Log(10) concentration (mol.1-¹) Figure 1 Surface tension as a function of log(10) concentration for three cationic surfactants with the same head group but varying hydrocarbon tail groups Figure 1 above shows surface tension against log10 concentration for a cationic surfactant series in 0.1 mol.L-¹ sodium chloride solution. The surfactants all have the same head- group but have different length hydrocarbon tail groups, which are linear alkyl chains, namely C12, C14 and C16. The data were taken at 300 K a) What are the critical micelle concentrations, cmc's, for these three surfactants? 6 marks b) Why are they different for different hydrocarbon chain lengths? 4 marks c) What is the surface excess for the three surfactants at a surface tension of 45 mN.m-¹? 10 marks d) lonic surfactants of this type generally form oil in water emulsions, how would you go about modifying the system so that a water in oil emulsion would form. You cannot change the surfactant type. 5 marks e) Non-ionic ethoxylated surfactants of the form Cx(CH2CH2O)y can also form both types of emulsions, in this case how does the nature of the hydrophilic group change to enable this to occur? 5 marks Surface tension (mN m²¹) 30 marks 35 30 25