2.7. The table shows the measured surface tension of aqueous solutions of dodecyldimethylammonium chloride at 293...

 

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2.7. The table shows the measured surface tension of aqueous solutions of dodecyldimethylammonium chloride at 293 K for (a) no added salt and (b) 0.20 M NaCl solution. No Salt C(M) x 10-5 x 10-5 1 8 3 x 10-4 1.0 x 10-3 2.0 × 10-3 3.5 x 10-3 5.6 x 10-3 9.5 x 10-3 1.1 x 10-2 1.4 x 10-2 2.0 × 10 2 4.0 x 10-² y(mJ/m²) 72 71.5 71 68 64 58 52 45 41 37.5 37.5 37.5 0.20 M NaCl C(M) 1 x 10-5 1.5 x 10-5 5 x 10-5 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 y(mJ/m²) 72 70 66 58 52 46 40 35 34 34 34 Why does the surface tension go to a constant value at high concentration? Give an answer both with respect to molecular events and in relation to the Gibbs adsorption equation. 2.8. Use the data of Exercise 2.7 to estimate the surface excess and area per molecule at c = 1 x 10-³ M and c=1.4 x 10-2M for the salt-free case. 2.7. The table shows the measured surface tension of aqueous solutions of dodecyldimethylammonium chloride at 293 K for (a) no added salt and (b) 0.20 M NaCl solution. No Salt C(M) x 10-5 x 10-5 1 8 3 x 10-4 1.0 x 10-3 2.0 × 10-3 3.5 x 10-3 5.6 x 10-3 9.5 x 10-3 1.1 x 10-2 1.4 x 10-2 2.0 × 10 2 4.0 x 10-² y(mJ/m²) 72 71.5 71 68 64 58 52 45 41 37.5 37.5 37.5 0.20 M NaCl C(M) 1 x 10-5 1.5 x 10-5 5 x 10-5 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 y(mJ/m²) 72 70 66 58 52 46 40 35 34 34 34 Why does the surface tension go to a constant value at high concentration? Give an answer both with respect to molecular events and in relation to the Gibbs adsorption equation. 2.8. Use the data of Exercise 2.7 to estimate the surface excess and area per molecule at c = 1 x 10-³ M and c=1.4 x 10-2M for the salt-free case.