(tp5647) padilla Homework 10 Sutclie (53770)
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001 10.0 points The theory used to explain the behavior of solids, liquids and gases is 1. the molecular theory. 2. the kinetic-molecular theory. correct 3. the VSEPR theory. 4. the atomic theory.
H H Which statement is correct? 1. The hydrogen bond B is stronger than the covalent bond A. 2. The covalent bond A is stronger than the hydrogen bond B. correct 3. The hydrogen bond A is stronger than the covalent bond B. 4. The covalent bond B is stronger than the hydrogen bond A. Explanation:
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Explanation: 002 10.0 points Which one of the following statements does NOT describe the general properties of liquids accurately? 1. The liquid state is highly disordered compared to the solid state. 2. A liquid sample has a characteristic volume that does not change greatly with changes in pressure. 3. A liquid sample has a characteristic volume that does not change greatly with changes in temperature, assuming that the liquid is not vaporized. 4. Liquids diuse only very slowly when compared to solids. correct 5. Liquids have high densities compared to gases.
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A is a covalent bond while B is a hydrogen bond. Covalent bonds are much stronger than H-bonds. 004 10.0 points Assign the strongest relevant intermolecular force to the following species, respectively: RbCl2 , C6 H6 (benzene), HI, Fe2 O3 , CH2 NH. I) ionic forces II) hydrogen bonding III) dipole-dipole IV) van der Waals forces 1. III, IV, I, I, II 2. I, II, IV, I, III
Explanation: Liquids diuse slowly; however, solids dont diuse well at all. 003 10.0 points Consider the two water molecules
3. II, IV, III, IV, IV 4. I, II, III, II, I 5. III, II, IV, III, III
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A B
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This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page nd all choices before answering.
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padilla (tp5647) Homework 10 Sutclie (53770) 6. I, IV, III, I, II correct 7. I, III, III, IV, II Explanation: Rubidium Chloride and Iron(III) oxide are both ion-ion. Benzene is non-polar and thus has only van der Waals forces. Hydroiodic acid is polar and has dipole-dipole interactions. Methylimine has H-bonding. 005 10.0 points What would be the most signicant type of intermolecular forces in a liquid sample of uoroform (CHF3 )? 1. hydrogen bonding 2. dispersion 3. dipole-dipole correct 4. ionic 5. covalent Explanation: London forces, dispersion forces, van der Waals or induced dipoles all describe the same intermolecular force. London forces are induced, short-lived, and very weak. Molecules and atoms can experience London forces because they have electron clouds. London forces result from the distortion of the electron cloud of an atom or molecule by the presence of nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London forces and occur between polar covalent molecules due to charge separation. H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electronegative atoms F, O or N only. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding. CHF3 is a polar molecule that does not con006 10.0 points Which statement is FALSE?
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tain H bonds; therefore, dipole-dipole forces will be the most signicant type of intermolecular forces present.
1. All other factors being equal, if adhesive forces are strong, capillary action is likely to occur less readily than if adhesive forces are weak. correct 2. In the absence of a phase change, the viscosity of a liquid increases as temperature decreases. 3. The shape of a meniscus depends on the dierence between the strengths of cohesive forces and adhesive forces. 4. Evaporation of liquids can occur below their normal boiling points at one atmosphere pressure. 5. High heats of vaporization are associated with liquids that have strong cohesive forces. Explanation: Forces of attraction between a liquid and a surface are called adhesive forces. When these forces are strong, capillary action is more likely to occur. 007 10.0 points Because the forces acting on molecules at the surface of a liquid are not equal in all directions, the liquid exhibits a property known as 1. surface tension. correct 2. capillary action. 3. density. Explanation: Molecules on the surface of a liquid are inuenced by intermolecular attractions towards the interior; these attractions pull the surface layer toward the center. The most sta-
padilla (tp5647) Homework 10 Sutclie (53770) ble situation is one in which the surface area is minimal. For a given volume, a sphere has the least possible surface area. Surface tension is a measure of the inward forces that must be overcome to expand the surface of a liquid. 008 10.0 points Substances have properties that are related to their structures. Which of the following statements regarding properties of solids is NOT expected to be correct? 1. Solid sodium should be a good conductor of electricity. 2. Diamond should have a high melting point. 3. Molten KBr should be a good conductor of electricity. 4. Solid CaF2 should have a low melting point. correct 5. Silicon dioxide should not sublime readily. Explanation: 009 10.0 points For which of the following is the type of solid INCORRECTLY given? 1. H2 O, molecular solid 2. CsI, covalent solid correct 3. KF, ionic solid 4. Ni, metallic solid 5. C6 H6 , molecular solid Explanation: CsI is an ionic solid. An ionic bond is a bond between a cation Cs+1 and an anion I1 . 010 10.0 points In which of these compounds would you nd
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ONLY dispersion forces existing between the molecules? I. CO2 ; II. CH2 Cl2 ; III. NH3 ; IV. CCl4 . 1. I and IV only correct 2. IV only 3. II and III only 4. I and II only 5. III and IV only 6. II only 7. III only 8. I only 9. I and III only 10. II and IV only Explanation: A nonpolar covalent molecule would have only dispersion forces with another nonpolar covalent molecule. 011 10.0 points Surface tension explains which of the following phenomena? I) A piece of aluminum foil oating on a lake II) A bowling ball sinking more slowly through molasses than through water III) Separating ethanol from water by distillation IV) Water beading on a windshield during the rain 1. III only 2. II and III only 3. I only
padilla (tp5647) Homework 10 Sutclie (53770) 4. I and II only 5. I and IV correct 6. II only 1. False correct 7. I and III only 2. True 8. III and IV only Explanation: A blowing balls rate of descent through a liquid is determined by the viscosity of the liquid. Distillation is a consequence of eater and ethanol having dierent vapor pressures. 012 10.0 points Rank the compounds NH3 , N2 , C2 H6 , NCl3 , H2 in terms of decreasing capillary action in a glass tube. 1. NH3 , N2 , C2 H6 , NCl3 , H2 2. H2 , N2 , C2 H6 , NCl3, NH3 3. NCl3 , C2 H6 , N2 , NH3 , H2 4. NH3 , C2 H6 , N2 , NCl3 , H2 5. NH3 , NCl3, C2 H6 , N2 , H2 correct Explanation: Capillary action is based on how attached molecules are to the electron rich oxygens in glass. Molecules with weak intermolecular forces will show very little capillary action. Molecules with strong intermolecular forces will climb very high in a glass tube. Hydrogen NH3 Strongest Strongest Bonding Dipole NCl3 Dipole Instantaneous C2 H6 largest Dipole N2 to H2 smallest Weakest 013 10.0 points CH3 F, C2 H6 , H2O, H2 , He in terms increasing of viscosity. 1. H2 , He, CH3F, H2 O, C2 H6 2. None of the answers is correct. 3. H2 O, CH3 F, C2 H6 , H2 , He 4. C2 H6 , H2O, CH3 F, He, H2 5. He, H2, C2 H6 , CH3F, H2 O correct
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A certain liquid has a meniscus that curves downward in glass. This means that the cohesive forces in the liquid are less than the forces between the liquid and the glass.
Explanation: If the meniscus of the liquid curves downward in glass (i.e., was convex), the liquid has tried to minimize its contact with the glass because the adhesive forces were weaker than the cohesive forces. 014 10.0 points Rank the molecules
Explanation: The intermolecular attractions, ranked from weakest to strongest, are London forces (also called van der Waals forces or induced dipoles), dipole-dipole interactions, hydrogen bonding interactions, and ion-ion interactions. In general, the larger the molecule, the greater the total intermolecular forces. Strong intermolecular interactions cause molecules to stick to one another, and are thus more viscous than molecules that experience weak intermolecular attractions. H2 O has two O H bonds which can hydrogen bond with neighboring water molecules. H, CH3 F is polar but contains no O N H , or F H bonds to participate in
padilla (tp5647) Homework 10 Sutclie (53770) hydrogen bonding. Therefore the strongest intermolecular forces that CH3 F experiences are dipole-dipole interactions. He, H2 , and C2 H6 are nonpolar and thus experience only the weakest intermolecular forces, London forces. 015 10.0 points As we increase the temperature of a liquid, its properties change. Which of the following would NOT be an expected change in the properties of a typical liquid as we increase its temperature? 1. increase in surface tension correct 2. increase in vapor pressure 3. increase in tendency to evaporate 4. decrease in density 5. decrease in viscosity Explanation: As temperature increases, molecules have more energy to overcome intermolecular forces/bonds. Therefore viscosity, surface tension and density will decrease and vapor pressure and rate of evaporation will increase. 016 10.0 points Water boils at a lower temperature at high altitudes. The most likely explanation for this is that at high altitudes 1. more energy is available to break liquid bonds. 2. the atmospheric pressure is lower than at low altitudes. correct 3. the temperature is higher than at low altitudes. 4. the vapor pressure of water is increased. Explanation: 1. 8.5 torr. 017 10.0 points Rank the following liquids in terms of increas2. greater than 34 torr.
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ing vapor pressure: C5 H12 , CH4 , C3 H8 , C2 H6 , C4 H10 . 1. CH4 < C2 H6 < C4 H10 < C3 H8 < C5 H12 2. C5 H12 < C4 H10 < C3 H8 < C2 H6 < CH4 correct 3. CH4 < C2 H6 < C3 H8 < C4 H10 < C5 H12 4. C5 H12 < C3 H8 < C4 H10 < C2 H6 < CH4 5. CH4 < C2 H6 < C3 H8 < C5 H12 < C4 H10 Explanation: All of these molecules are non-polar so their strongest IMF is London Dispersion forces. To rank their IMFs then, we remember that larger molecules exhibit stronger London Dispersion forces. Then, remembering that vapor pressure is inversely proportional to IMF, we simply rank them from largest to smallest 018 10.0 points A liquid with a high vapor pressure is called 1. cold. 2. viscous. 3. volatile. correct 4. hot. Explanation: Easily vaporized liquids are called volatile liquids, and they have relatively high vapor pressures. 019 10.0 points Consider two empty containers A and B whose volumes are 10 mL and 20 mL, respectively. You now put 1 mL of liquid H2 O into each container and adjust the temperature of each container to 20 C. The gas pressure in container B is found to be 17 torr. The gas pressure in container A is
padilla (tp5647) Homework 10 Sutclie (53770) 3. 34 torr. 4. between 17 and 34 torr. 5. 17 torr. correct Explanation: T = 20 C + 273 = 293 K 1 atm P = 17 torr = 0.02237 atm 760 torr 1 g H2 O 1 mol H2 O n = 1 mL H2 O 1 mL H2 O 18 g H2 O = 0.0555 mol H2 O Every liquid shows a characteristic vapor pressure that varies only with temperature, and not with the volume of vapor present, as long as both liquid and vapor are present and at equilibrium. Ideal Gas Law relates the volume and pressure of a sample of gas: P V = nRT nRT V= P Latm (0.0555 mol)(0.082058 molK )(293 K) = (0.02237 atm) = 59.65 L Thus there must still be liquid left in each container and the pressure will be the vapor pressure. 020 10.0 points Real gases and vapors have intermolecular interactions. Recall that the van der Walls equation is expressed in terms of two parameters a and b. Which of Br2 or F2 has the larger van der Walls parameter b? 1. They are the same. 2. F2 3. Br2 correct Explanation: b represents the volume of the molecule itself. Br2 is larger, leading to a larger b. 021 10.0 points
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List the gases H2 , CH3 F, N2 , CF4 , HF in order of DECREASING tendency to behave as ideal gases. (Consider only intermolecular forces in determining non-ideality.) 1. HF, CH3 F, CF4 , N2 , H2 2. CF4 , CH3 F, N2 , HF, H2 3. H2 , N2 , CF4 , CH3 F, HF correct 4. H2 , HF, N2 , CH3 F, CF4 5. H2 , CH3 F, N2 , CF4 , HF Explanation: The stronger the intermolecular forces present, the greater the non-ideality: H2 N2 CF4 Dipoledipole CH3 F HF HBonding Induced Dipole smallest, most ideal largest least ideal
022 10.0 points All of the following are gases at room temperature and atmospheric pressure. Which one will liquify most easily when pressurized at a certain temperature? 1. NH3 correct 2. F2 3. SiH4 4. Ar 5. H2 Explanation: H2 , Ar, SiH4 and F2 are non-polar. NH3 is polar and experiences stronger attractive forces, which aid in liquication. 023 10.0 points Gas X has a larger value than Gas Y for the
padilla (tp5647) Homework 10 Sutclie (53770) van der Waals constant a. This indicates that 1. the molecules of gas X have a higher velocity than do the molecules of gas Y. 2. the molecules of X are larger than the molecules of Y. 3. the molecules of X have stronger intermolecular attractions for each other than the molecules of Y have for each other. correct 4. the molecules of gas X repel other X molecules. Explanation: 024 10.0 points Which of the following molecules would have the smallest a and b term, respectively, in the van der Waals equation: O3 , CHF3, SF5 Cl, SiHCl3, Xe. 1. Xe and O3 , respectively correct 2. CHF3 and CHF3 , respectively 3. Xe and SF5 Cl, respectively 4. SiHCl3 and O3 , respectively 5. Xe and Xe, respectively Explanation: Xenon is the only non-polar species and thus would have the smallest a term. Ozone is the smallest in terms of molecular weight and would thus have the smallest b term. 025 10.0 points Which of the following covalent network solids conducts electricity? 1. glass 2. graphite correct 3. cellulose 4. starch 5. diamond
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Explanation: Graphite is the only choice that contains bonds. 026 10.0 points In which one of the following is hydrogen bonding NOT a factor? 1. NH3 2. H2 O 3. CH4 correct 4. CH3 OH Explanation: 027 10.0 points What is the strongest evidence for hydrogen bonding? 1. Hydrogen can be considered either a metal or nonmetal. 2. Hydrogen has an extremely low electronegativity. 3. The boiling points of NH3 , H2 O, and HF are abnormally high compared with the rest of the hydrides in their respective periods. correct 4. Hydrogen is able to accept or donate electrons, so it is the most versatile atom in the periodic chart. Explanation: