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13 Properties of Solutions Solutions to Exercises 13.107 0.015 1L blood N₂ 1 mol N₂ = 5.355 10⁻⁴ = 5.4 10⁻⁴ mol blood 28.01 g N₂ At 100 ft, the partial pressure of N₂ in air is 0.78 (4.0 atm) = 3.12 atm. This is just four times the partial pressure of N₂ at 1.0 atm air pressure. According to Henry's law, = kP₈, a 4-fold increase in P₈ results n a 4-fold increase in Sg, the solubility of the gas. Thus, the solubility of N₂ at 100 ft is 4(5.355 M) = 2.142 10⁻³ = 2.1 10⁻³ M. If the diver suddenly surfaces, the amount of blood released is the difference in the solubilities at the two depths: (2.142 X 10⁻³ mol/L - 5.355 10⁻⁴ mol/L) = 1.607 X = 1.6 10⁻³ mol blood. At surface conditions of 1.0 atm external pressure and 37°C = 310 K, V = nRT P = 1.607 10⁻³ mol 310K atm 0.08206 mol K atm = 0.041 L That is, 41 mL of tiny N₂ bubbles are released from each L of blood. 13.108 The stronger the intermolecular forces, the higher the heat (enthalpy) of vaporization. (a) None of the substances are capable of hydrogen bonding in the pure liquid, and they have similar molar masses. All intermolecular forces are van der Waals forces, dipole-dipole, and dispersion forces. In decreasing order of strength of forces: acetone > acetaldehyde > ethylene oxide > cyclopropane The first three compounds have dipole-dipole and dispersion forces, the last only dispersion forces. (b) The order of solubility in hexane should be the reverse of the order above. The least polar substance, cyclopropane, will be most soluble in hexane. Ethanol, is capable of hydrogen bonding with the three polar compounds. Thus, acetaldehyde, acetone, and ethylene oxide should be more soluble than cyclopropane, but without further information we cannot distinguish among the polar molecules. cation (g) + anion (g) + solvent 13.109 (a) solvation energy of gaseous ions U = lattice energy solution ionic solid + solvent (b) If the lattice energy (U) of the ionic solid (ion-ion forces) is too large relative to the solvation energy of the gaseous ions (ion-dipole forces), will be too large and positive (endothermic) for solution to occur. This is the case for solutes like NaBr. Lattice energy is inversely related to the distance between ions, so salts 391