SECTION A Question 1 The variation of surface tension (y) with In concentration (In c) for a number of non-ionic surfactants of general formula C12H25(OC2H4) mOH (designated C12Em) was measured. The resulting profiles had negative slopes. Their gradients at the critical micelle concentration, CMC, at 298 K are given in Table 1. The typical structure of C12E4 compared to that of C12E6 is shown in Figure 1. dy dlnc C12E6 C12E4 non-ionic Polyoxyethylene alkyl ethers (CnEm), n = 12 and m = 4, 6 Figure 1. Typical structure of non-ionic surfactants of general formula C12H25(OC2H4) OH (designated C₁2E) for m = 4 and 6 are shown Compound dy dlnc (Nm-¹) CMC 105 (mol dm³) C12E3 1.14 x 10-2 3 C12E4 9.34 x 10-3 5 C12E5 8.15 x 10-3 6 C12E6 7.48 x 10-3 8.5 C12E8 6.74 x 10-3 8 Table 1. Gradient (- dy -) for C12Em surfactants and their critical dlnc micelle concentrations, CMC measured by surface tension. (a) Use the Gibbs equation to calculate the adsorbed amount (T/mol m²) of each surfactant at its CMC and hence determine the area occupied (A) by each molecule at the CMC. [10 marks] Useful information: R-8.314JK'mol F-9.645-10°C mol (or V₁t's mol) No 6022-10 me SECTION A Question 1 The variation of surface tension () with In concentration (In c) for a number of non-ionic surfactants of general formula CH(OCH) OH (designated CE) was measured. The resulting profiles had negative slopes. Their gradients (), at the critical micelle concentration, CMC, at 298 K are given in Table 1. The typical structure of CE compared to that of CE is shown in Figure 1. СЕ non-ionic Polyoxyethylene alkyl ethers (CnEm), n 12 and m 4,6 Figure 1. Typical structure of non-ionic surfactants of general formula CH(OCH) OH (designated CE) for m-4 and 6 are shown Compound (Nm) CMC 10 (mol dm) CE 1.14x102 CE 9.34x10 CE 8.15x10 CE 7.48 x 10 CE 3 6 8.5 Table 1. Gradient ( 6.74 x 10 for CE surfactants and their critical micelle concentrations, CMC measured by surface tension. (a) Use the Gibbs equation to calculate the adsorbed amount (I/mol m²) of each surfactant at its CMC and hence determine the area occupied (A) by each molecule at the CMC. [10 marks]