Page 1308 - Chemistry--atom first

1298 Answer Key
73. (b) metallic solid
75. The structure of this low-temperature form of iron (below 910 °C) is body-centered cubic. There is one-eighth
atom at each of the eight corners of the cube and one atom in the center of the cube. 77. eight
79. 12
81. (a) 1.370 Å; (b) 19.26 g/cm
83. (a) 2.176 Å; (b) 3.595 g/cm3
85. The crystal structure of Si shows that it is less tightly packed (coordination number 4) in the solid than Al
(coordination number 12).
87. In a closest-packed array, two tetrahedral holes exist for each anion. If only half the tetrahedral holes are occupied, the numbers of anions and cations are equal. The formula for cadmium sulfide is CdS.
89. Co3O4
91. In a simple cubic array, only one cubic hole can be occupied be a cation for each anion in the array. The ratio of
thallium to iodide must be 1:1; therefore, the formula for thallium is TlI. 93. 59.95%; The oxidation number of titanium is +4.
95. Both ions are close in size: Mg, 0.65; Li, 0.60. This similarity allows the two to interchange rather easily. The difference in charge is generally compensated by the switch of Si4+ for Al3+.
97. Mn2O3
99. 1.48 Å
101. 2.874 Å
103. 20.2°
105.1.74 104 eV
Chapter 11
1. A solution can vary in composition, while a compound cannot vary in composition. Solutions are homogeneous at
the molecular level, while other mixtures are heterogeneous.
3. (a) The process is endothermic as the solution is consuming heat. (b) Attraction between the K+ and ions is stronger than between the ions and water molecules (the ion-ion interactions have a lower, more negative energy).
Therefore, the dissolution process increases the energy of the molecular interactions, and it consumes the thermal energy of the solution to make up for the difference. (c) No, an ideal solution is formed with no appreciable heat release or consumption.
5. (a) ion-dipole forces; (b) dipole-dipole forces; (c) dispersion forces; (d) dispersion forces; (e) hydrogen bonding
7. Heat is released when the total intermolecular forces (IMFs) between the solute and solvent molecules are stronger than the total IMFs in the pure solute and in the pure solvent: Breaking weaker IMFs and forming stronger IMFs releases heat. Heat is absorbed when the total IMFs in the solution are weaker than the total of those in the pure solute and in the pure solvent: Breaking stronger IMFs and forming weaker IMFs absorbs heat.
9. Crystals of NaCl dissolve in water, a polar liquid with a very large dipole moment, and the individual ions become strongly solvated. Hexane is a nonpolar liquid with a dipole moment of zero and, therefore, does not significantly interact with the ions of the NaCl crystals.
11. (a) Fe(NO3)3 is a strong electrolyte, thus it should completely dissociate into Fe3+ and ions. Therefore, (z) best represents the solution. (b)
13. (a) high conductivity (solute is an ionic compound that will dissociate when dissolved); (b) high conductivity (solute is a strong acid and will ionize completely when dissolved); (c) nonconductive (solute is a covalent compound, neither acid nor base, unreactive towards water); (d) low conductivity (solute is a weak base and will partially ionize when dissolved)
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