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13 Properties of Solutions Solutions to Exercises with large cations like (CH₃)₄l have smaller lattice energies than salts with simple cations like The smaller lattice energy of NBr causes it to be more soluble in nonaqueous polar solvents. Also, the -CH₃ groups in the large cation are capable of dispersion interactions with the -CH₃ (or other nonpolar groups) of the solvent molecules. This produces a more negative solvation energy for the salts with large cations. Overall, for salts with larger cations, U is smaller (less positive), the solvation energy of the gaseous ions is more negative, and is less endothermic. These salts are more soluble in polar nonaqueous solvents. 13.110 (a) Zn(s) 2.050 Zn 65.39 1 mol Zn = 0.03135 mol Zn 1.00 M 0.0150 = 0.0150 mol Since Zn and react in a 1:1 mole ratio, is the limiting reactant; 0.0150 mol of H₂(g) are produced. (b) P = nRT V = 0.0150 K atm 298 = 3.0066 = 3.01 atm (c) L-atm 3.0066 atm = 0.002345 = 2.3 10⁻³ M 0.002345 mol H₂ 0.0150 = 3.518 10⁻⁵ = 3.5 10⁻⁵ mol dissolved H₂ L soln 3.5 10⁻⁵ mol dissolved H₂ 100 = 0.23% dissolved 0.0150 mol H₂ produced This is approximately 2.3 parts per thousand; for every 10,000 H₂ molecules, 23 are dissolved. It was reasonable to ignore dissolved H₂(g) in part (b). 13.111 (a) 1.3 X 10⁻³ mol X = 5.2 10⁻³ mol CH₄ soln V = nRT P = 5.2 10⁻³ mol 0.08206 mol K atm (b) All three hydrocarbons are nonpolar; they have zero net dipole moment. In and C₂H₆, the atoms are tetrahedral and all bonds are σ bonds. has a higher molar mass than CH4, which leads to stronger dispersion forces and greater water solubility. In the atoms are trigonal planar and the π electron cloud is symmetric above and below the plane that contains all the atoms. This planar arrangement facilitates contact between molecules, leading to stronger dispersion forces. The π cloud in is an area of concentrated electron density that experiences attractive forces with the positive ends of molecules. These forces increase the solubility of relative to the other hydrocarbons. 392