Property Water n-Pentane Molecular weight (g/mol) 18.02 72.15 Density (g/cm) 0.997 0.626 Boiling point (°C) 100 36.1 Dielectric constant 78.3 1.84 Viscosity (g/cm · s) 0.890 x 10-2 0.228 x 10-2 Surface tension (dyne/cm) 71.97 17

Suppose a chloride ion and a sodium ion are separated by a center–center distance of 5 Å. Is the interaction energy (the energy required to pull them infinitely far apart) predicted to be larger if the medium between them is water, or if it is n-pentane? If Ca ²⁺, Na⁺, and F ^- each have ionic radii ∙1.16. Which ionic bond is stronger: Ca-F or Na-F? If Ca ²⁺ is often bound on the surface of a protein by carboxylic acid functional groups. If the pK_a of a particular ¬COOH group is 4.2, would you predict Ca ²⁺ to be most tightly bound at pH 8, pH 4.2, or pH 3? Explain your answer.