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Unformatted text preview: Chem120B Problem Set 10 Due: April 22, 2011 1. (i) 0.1 moles of NaCl are dissolved in 1 L of water at room temperature. Compute the Debye screening length of the solution. Compare your result with the following lengths: (i) ρ- 1 / 3 w (ii) ρ- 1 / 3 I (iii) βe 2 / ( ǫ 4 πǫ ) where ρ w is the density of water (i.e., the number of molecules per unit volume), ρ I is the density of ions, e is the charge of a monovalent ion, and ǫ ≈ 80 is the dielectric constant of liquid water. Comment on the physical significance of each length (e.g., ρ- 1 / 3 I is roughly the average distance between an adjacent pair of ions). (ii) Let w ( r ) be the reversible work required to move a Na + ion from ∞ to a distance r away from a Cl- ion. Evaluate w ( r ) for a typical distance between adjacent ions. Also evaluate w ( r ) for r = 3 ˚ A, the ionic bond length between an undissociated Na + Cl- pair....
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