Gibbs adsorption equation (15 points) The table below shows the measured surface tension of aq. solution of surfactant dodecyldimethylammonium chloride from (a) no added salt and (b) 0.20 M NaCl solution. Assume 20oC temperature

Estimate the surface excesses and areas/molecule at c1 = 0.001 M and c2 = 0.014 M in both (a) and (b) cases. Discuss the difference between no salt and NaCl results. Explain what happens at high concentrations?

No Salt 0.20 M NaCl C(M) y(mJ/m2) C(M) y(mJ/m) 1 8 x 10-5 o x 10-5 x 10-5 X 10-4 72 71.5 71 68 72 70 66 3 x 10-5 1.0 x 107 2.0 x 10-3 3.5 x 10-3 5.6 x 10-3 9.5 x 10? 1.1 x 10-2 1.4 x 10-2 2.0 x 10-2 4.0 x 10-2 1 1.5 x 10-5 5 1.6 x 10-4 4.0 x 10-4 9.0 x 10-4 1.5 x 10-3 2.5 x 10-3 3.9 X 10-3 5.0 x 10-3 4.0 x 10-2 64 58 52 45 41 37.5 37.5 37.5 - 58 52 46 40 35 34 34 34