110209 - 1 CHM3400 - Lecture 14 – Feb 9 Electrolyte...

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Unformatted text preview: 1 CHM3400 - Lecture 14 – Feb 9 Electrolyte solutions (Chapter 5 p. 154-170) • Electrostatic interactions between ions: vacuum and solution (dielectric constant) • Enthalpy, entropy and Gibbs free energy of ions in solution • Ionic activity • Debye-Huckel Law Electrolyte= substance, that when dissolved in solution, makes the solution conduct electricity 2 Hydration shell Ion-dipole interactions between ions and the water solution Why does NaCl dissolve in water, but not in benzene? Mean life-time of an H 2 O molecule in the solvation shell: Br- 10-11 s Na + 10-9 s Fe 3+ 10-5 s Al 3+ 7 s Cr 3+ 1.5x10 5 s Ionic radii of hydrated cations: Li + (3.66 Å), Na + (2.80 Å) and K + (1.87 Å) 3 Ionic interaction: vacuum vs. solution Vacuum: 2 4 r q q F Cl Na πε − + = Attractive force: ε = permittivity of the vacuum (= 8.854x10-12 C 2 N-1 m-2 ) Solution: 2 4 r q q F Cl Na ε πε − + = Attractive force: ε = permittivity of the medium (no units) Solvent molecules shield the charges from each other For NaCl pair: 4 Example 5.7 Calculate the force in Newtons between a pair of Na + and Cl- ions separated by exactly 1 nm (10 Å) in (a) a vacuum and (b) water at 25 o C. The charges on the Na + and Cl- are the elemental charges respectively. (1.602x10-19 C) 2 4 r q q Cl Na vac πε − + = ) ( 10 31 . 2 ) ( ) ( ) 10 1 ( 10 854 . 8 4 ) 10 602 . 1 ( 10 602 . 1 10 2 2 1 2 2 9 12 19 19 N m m N C C C − − −...
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This note was uploaded on 05/29/2011 for the course CHM 3400 taught by Professor Seabra during the Spring '08 term at University of Florida.

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110209 - 1 CHM3400 - Lecture 14 – Feb 9 Electrolyte...

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