CHM 130 Chapter 13 Homework Answers

1) Check all of the examples below that are properties of liquids: b) Indefinite shape but a fixed volume c) Flow readily e) Cannot expand or compress f) If miscible, can mix uniformly to form a homogeneous mixture 2) Check all of the examples below that are properties of solids: a) Definite shape and fixed volume e) Cannot expand or compress g) Lacks the energy to mix, so cannot mix by diffusion h) Can be crystalline or noncrystalline 3) Intermolecular forces or bonds exist between _____________. d) two different molecules 4) Check all of the following that are types of intermolecular forces: d) Hydrogen bond e) Induced dipole (dispersion or London) forces f) Dipole forces Explanation Intermolecular forces refer to the attraction between two different molecules. The types of intermolecular forces are: Hydrogen bond, Induced dipole (dispersion or London) forces , and Dipole forces The other choices (ionic bond, polar covalent bond, and nonpolar covalent bond) are all intramolecular forces that exist between two ions or atoms within a compound. 5) The attractions between nonpolar molecules in liquids or solids that are temporary dipoles known as ____________. c) induced dipole (dispersion or London) forces Explanation The attractions between nonpolar molecules in liquids or solids are temporary dipoles known as induced dipole (dispersion or London) forces . 6) The attraction between polar molecules in liquids or solids that do not contain a H-F, H-O, or H-N bond is known as _______________________. d) dipole forces Explanation The attraction between polar molecules in liquids or solids is known as dipole forces . 7) The strongest attraction between polar molecules in liquids or solids that contain a H-F, H-O, or H-N bond is known as ____________. e) hydrogen bonds Explanation The strongest attraction between polar molecules in liquids or solids that contain a H-F, H-O, or H-N bond is known as hydrogen bonds . 8) Check all of the examples below that are polar: a) HF d) NO f) CO h) H2O 1 of 6 Explanation The following molecules all have overall (or net) dipoles, so they are polar: HF, NO, CO, H2O 9) Check all of the examples below that are polar: a) NH3 d) H2S e) H2O f) HF g) HCl Explanation The following molecules all have overall (or net) dipoles, so they are polar: NH3, H2S, H2O, HF, HCl 10) Check all of the statements below that are correct: b) Dipole forces are stronger than induced dipole (dispersion or London) forces for molecules of similar size. e) Ionic bonds hold ions together in an ionic compound, and covalent bonds hold atoms together in a molecule. Explanation The following statements are correct: • Dipole forces are stronger than dispersion (or London) forces for molecules of similar size. – Because dipole forces are the attraction between molecules with permanent dipoles, they are stronger than induced dipole (dispersion or London) forces that are the result of temporary dipoles between nonpolar molecules. However, very large nonpolar molecules have more electrons that can often be polarized to have large dipoles. Thus, very large nonpolar molecules (with many electrons) can often experience stronger intermolecular attractions than the dipole forces experienced between very small polar molecules. • Ionic bonds hold ions together in an ionic compound, and covalent bonds hold atoms together in a molecule. – Ionic bonds are the electrostatic attraction holding ions together in an ionic compound. Covalent bonds are the sharing of one of more pairs of electrons by two nonmetal atoms in a molecule or molecular compound. The following statements are incorrect: • Hydrogen bonds are stronger than ionic and covalent bonds. – Although hydrogen bonds are the strongest type of intermolecular force, ionic and covalent bonds that hold ions and atoms together in compounds are stronger than hydrogen bonds. • The H-H bond in a hydrogen molecule is an example of an induced dipole (dispersion or London) force. – The H-H bond in a hydrogen molecule is a nonpolar covalent bond. The attraction between two different hydrogen molecules would be an induced dipole (dispersion or London) force. • The N-H bond in NH3 is an example of hydrogen bonding. – The N-H bond in NH3 is a polar covalent bond. The attraction between two NH3 molecules would be hydrogen bonding. 11) Check all of the examples below which experience only induced dipole (dispersion or London) forces. b) CCl4 (l) c) Br2 (l) Explanation Nonpolar molecules experience only induced dipole (dispersion or London) forces, and of the examples above, only CCl4 (l) and Br2 (l) are nonpolar. 12) Check all of the examples below which experience dipole forces but not hydrogen bonds: d) H2S (l) g) HCl (l) Explanation Polar molecules that do NOT contain H-F, H-O, or H-N bonds experience dipole forces but not hydrogen bonds. Of the examples above, only H2S (l) and HCl (l) are polar with no H-F, H-O, or H-N bonds. 2 of 6 13) Check all of the examples below which experience hydrogen bonds: a) NH3 (l) e) H2O (l) f) HF (l) Explanation Only polar molecules with H-F, H-O, and H-N bonds experience hydrogen bonds. Of the examples above, only NH3 (l), H2O (l), and HF (l) experience hydrogen bonds. 14) Water molecules experience hydrogen bonds whereas ethyl ether molecules experience only induced dipole (dispersion or London) forces. Check all of the statements below that are true: a) Water's intermolecular forces are stronger than ethyl ether's. c) Water has a higher boiling point compared to ethyl ether. d) Water has a higher surface tension compared to ethyl ether. e) Water has a higher viscosity compared to ethyl ether. Explanation Since hydrogen bonds are stronger intermolecular forces than induced dipoles forces, water will have stronger intermolecular forces, a higher boiling point, a higher surface tension, and a higher viscosity than ethyl ether. Vapor pressure is a measure of the number of gas molecules above the liquid. The stronger the intermolecular forces, fewer molecules escape from the liquid to the gaseous state, so strong intermolecular forces result in a lower vapor pressure. 15) Water molecules experience hydrogen bonds whereas hydrogen sulfide (H2S) molecules experience dipole forces. Check all of the statements below that are true: a) Water's intermolecular forces are stronger than H2S's. c) Water has a higher molar heat of vaporization compared to H2S. d) Water has a higher surface tension compared to H2S. e) Water has a higher viscosity compared to H2S. Explanation Since hydrogen bonds are stronger intermolecular forces than dipole forces, water will have stronger intermolecular forces, a higher molar heat of vaporization, a higher surface tension, and a higher viscosity than H2S. Vapor pressure is a measure of the number of gas molecules above the liquid. The stronger the intermolecular forces, fewer molecules escape from the liquid to the gaseous state, so strong intermolecular forces result in a lower vapor pressure. 16) Ethyl ether molecules experience only induced dipole (dispersion or London) forces whereas hydrogen sulfide (H2S) molecules experience dipole forces. Check all of the statements below that are true: a) Ethyl ether's intermolecular forces are weaker than H2S's. b) Ethyl ether has a higher vapor pressure compared to H2S. Explanation Since induced dipole (dispersion or London) forces are weaker intermolecular forces than dipole forces, ethyl ether will experience weaker attractions and have a lower boiling point, a lower surface tension, and a lower viscosity than H2S. Vapor pressure is a measure of the number of gas molecules above the liquid. The weaker the intermolecular forces, more molecules escape from the liquid to the gaseous state, so weak intermolecular forces result in a higher vapor pressure. 17) Acetone, which is the active ingredient in nail polish remover, boils at 56°F. Considering the boiling point of water, check all of the statements below that are correct: a) The intermolecular forces between water molecules are stronger than those between acetone molecules. b) Acetone's vapor pressure should be higher than water's. d) Acetone's viscosity should be lower than water's. Explanation The following statements are correct: • The intermolecular forces between water molecules are stronger than those between acetone molecules. • Acetone's vapor pressure should be higher than water's. 3 of 6 • Acetone's viscosity should be lower than water's. Since acetone has a lower boiling point than water, it must have weaker intermolecular forces compared to water. Thus, acetone would have lower surface tension and a lower viscosity than water. Vapor pressure is a measure of the number of gas molecules above the liquid. When the intermolecular forces are weaker, more molecules escape from the liquid to the gaseous state. Thus, because acetone's intermolecular forces are weaker, it should have higher vapor pressure than water. 18) What holds the atoms together in a CCl4 molecule is _____________. b) a polar covalent bond Explanation What holds the atoms together (i.e., the C-Cl bond ) in a CCl4 molecule is a polar covalent bond. 19) What holds two Br2 molecules together is _____________. d) an induced dipole (dispersion or London) force Explanation Since Br2 molecules are nonpolar, an induced dipole (dispersion or London) force holds two Br2 molecules together in a sample of Br2. 20) The bonds in K2O are _____________. a) ionic bonds Explanation The bonds in K2O are an ionic bonds. Since K is a metal and O is a nonmetal, K loses electrons to O to form K+ and O2- ions. The ions form a three-dimensional network of ions with a ratio of two K+ ions for every one O2- ion. 21) What holds two HBr molecules together is _____________. e) a dipole force Explanation What holds two HBr molecules together is a dipole force. Since HBr is a polar molecule that does not contain H-F, H-O, or H-N bonds required for hydrogen bonds, then the attraction between two HBr molecules is a dipole force. 22) What holds the atoms together in a water molecule is _____________. b) a polar covalent bond Explanation What holds the atoms together (i.e., the H-O bond ) in a H2O molecule is a polar covalent bond. 23) Check all the following that are examples of intermolecular forces: c) The bonds between two different water molecules in a sample of water. d) The bonds between two different HBr molecules in a sample of HBr(l). e) The bonds between two different CCl4 molecules in a sample of CCl4(l). Explanation The following are intermolecular forces: • The bonds between two different water molecules in a sample of water. (These are hydrogen bonds.) • The bonds between two different HBr molecules in a sample of HBr(l). (Since HBr is polar but does not contain H-F, H-O, or H-N bonds, the bonds between HBr molecules are dipole forces.) • The bonds between two different CCl4 molecules in a sample of CCl4(l). (Since CCl4 is a nonpolar molecule, the bonds between CCl4 are dispersion or London forces, also called induced-dipole forces.) The following are ionic or covalent bonds: • The bonds holding atoms together in HF are polar covalent bonds since H and F atoms have different electronegativity values. • The bonds holding atoms together in I2 are nonpolar covalent bonds since both I atoms have equal electronegativity values. • The bonds in NaCl are ionic bonds since Na is a metal and Cl is a nonmetal, so NaCl exists as a threedimensional network of Na+ and Cl- ions held together by electrostatic attraction. 4 of 6 24) Check all of the examples below that are molecular solids: c) iodine, I2 (s) e) diamond, a form of carbon f) ice, H2O (s) Explanation Molecular solids consist only of nonmetals. Thus, only I2 (s), H2O (s), and diamond are molecular solids. 25) Check all of the examples below that are ionic solids: b) magnesium oxide, MgO (s) g) table salt, NaCl (s) Explanation Ionic solids consist of a metal with one or more nonmetals. Thus, only MgO (s) and NaCl (s) are ionic solids. 26) Check all of the examples below that are metallic solids: a) nickel, Ni (s) d) copper wire, Cu (s) Explanation Metallic solids consist only of metals. Thus, only Ni (s) and Cu (s) are metallic solids. 27) The Lewis diagram for water shows: (Check all that apply.) a) 8 valence electrons c) 2 bonding and 2 nonbonding electron pairs d) single bonds from the oxygen to the hydrogen atoms Explanation The Lewis diagram for water shows the following: • 8 valence electrons • 2 bonding and 2 nonbonding electron pairs • single bonds from the oxygen to the hydrogen atoms. 28) Check all of the statements regarding water below that are true: b) Water has a bent molecular shape with a d) The H-O bond in water is a polar covalent bond with the δ– on the O and the δ+ on the H. g) Water is a polar molecule. h) Water molecules experience hydrogen bonds. j) The density of ice is lower than the density of water in the liquid state. Explanation The following statements for water are correct: • Water has a bent molecular shape with a - The four pairs of electrons around the O in water cause the molecule to have a bent structure, and bent molecules have bond angles that are • The H-O bond in water is a polar covalent bond with the δ– on the O and the δ+ on the H. • Water is a polar molecule. • Water molecules experience hydrogen bonds. • The density of ice is lower than the density of water in the liquid state. - At the atomic level, ice has holes in its structure because of hydrogen bonding between water molecules in ice. Thus, the density of ice is lower than the density of water in the liquid state. We know this from practical experience also because ice cubes will float in a glass of water. 29) Check all of the correct statements regarding the Heating-Cooling Curve below: 5 of 6 b) Region 2 contains both solid and liquid. c) Region 3 contains only liquid. e) Region 5 contains only gas. Explanation A correctly labeled Heating-Cooling Curve is shown below: 30) Check all of the correct statements below regarding the Heating-Cooling Curve in problem #29 above. c) A represents the melting point of the substance. d) B represents the boiling point of the substance. e) In regions 2 and 4, temperature remains constant while the substance is converted from one physical state to another. Explanation A correctly labeled Heating-Cooling Curve is shown in the feedback for problem #29 above. 6 of 6