CHAPTER 11 PRACTICE QUESTIONS 1. Crystals of elemental sulfur are easily crushed, and melt at 113°C. Liquid sulfur does not conduct electricity. What kind of crystal is this? 2. Which is expected to have a higher boiling point, C8H18 or C4H10? 3. mgO has the same crystal structure as NaCl, face-centered cubic. How many oxide ions surround each Mg2+ ion as nearest neighbors? A. 4 B. 6 C. 8 D. 10 E. 12 4. The molecular property related to the ease with which the electron density in a neutral atom or molecule can be distorted is called a. b. c. d. e. a dipole moment. polarizability. a dispersion force. surface tension. a van der Waals force. 5. Given the following liquids and their boiling points, which has the highest vapor pressure at its normal boiling point? a. b. c. d. e. ethanol bp = 78°C methanol bp = 65°C water bp = 100°C benzene bp = 80°C The vapor pressures of each of the liquids at its normal boiling point would be the same. 6. Magnesium oxide, MgO, melts at 2,800°C and is very hard. The liquid conducts electricity very well. What kind of crystal is this? 7. Which of the responses includes all of the following that can form hydrogen bonds with water molecules? 1. Na+ A. 2. CH3COOH 1, 2 B. 1, 3 3. C2H6 C. 4. CH3NH2 2, 3 D. 2, 4 E. 3, 4 8. The heat capacity for liquid water is 4.18 J/g·°C and the heat of vaporization is 40.7 kJ/mol. How many kilojoules of heat must be provided to convert one gram of liquid water at 67°C into one gram of steam at 100°C? 40.8 J A. 22.6 kJ B. 40.8 kJ C. 2.2 kJ D. 2,400 J E. 9. Sodium iodide, NaI, melts at 651°C. In its liquid state NaI conducts electricity. What kind of crystal is this? 10. Which one of the following substances should exhibit hydrogen bonding in the liquid state? E. CH3OH A. PH B. He C. H S D. CH 3 2 4 Page 1 11. Calculate the amount of heat that must be absorbed by 10.0 g of ice at -20°C to convert it to liquid water at 60.0°C. Given: Specific heat (ice) = 2.1 J/g·°C Specific heat (water) = 4.18 J/g·°C Hfus = 6.0 kJ/mol A. 420 J B. 2,900 J C. 6,300 J D. 63 kJ E. 7.5 J 12. Which of the following properties indicates the presence of strong intermolecular forces in a liquid? a. b. c. d. e. a low heat of vaporization a low critical temperature a low vapor pressure a low boiling point None of the above. 13. Potassium crystallizes in a body-centered cubic lattice. How many atoms are there per unit cell? E. 8 A. 1. B. 2 C. 4 D. 6 14. Which liquid is expected to have the larger surface tension at a given temperature, CCl4 or H2O? Briefly explain. 15. Boron nitride, BN3, melts at approximately at 3,000°C under high pressure. This materal is almost as hard as diamond. What kind of crystal is this? 16. The triple point of iodine is at 0.12 atm and 115°c. This means that liquid I2 a. is more dense than I2 (s). b. cannot exist above 115°C. c. is liquid at room temperature. d. cannot have a vapor pressure less than 90 torr. 17. Using the following phase diagram of a certain substance, in what phase is the substance at 50°C and 1 atm pressure? 18. Indicate all the types of intermolecular forces of attraction in the following compounds. a. F2(l) b. HF(l) c. SO2(l) d. He(l) are nonpolar. HCl Ar _____________________ _____________________ _____________________ _____________________ 19. Below are selected compounds and their boiling points. Identify which are polar and which -84.9°C -185.7°C F2 H2S -188.1°C -60.7°C 20. Helium atoms do not combine to form He2 molecules, yet He atoms do attract one another weakly through a. b. c. d. e. a. b. c. d. e. dipole-dipole forces. ion-dipole forces. dispersion forces. dipole-induced dipole forces. hydrogen bonding. diamond. potassium. iodine. sodium chloride. None of the above. 21. An example of a covalent network solid is 22. Which member of each pair would have the stronger intermolecular forces of attraction? Circle. a. H2S or H2Se b. HF or HCl c. CH4 or CH3OH d. NH3 or PH3 e. SF4 or C10H22 23. Which of the following atoms does not participate in hydrogen bonding? A. S B. O C. F D. N Page 3 24. Polyethylene plastic consists of long chains of carbon atoms, each of which is also bonded to hydrogens as shown below: H C H H H H H C C H C H C H C H H H Water forms beads when placed on a polyethylene surface. Why? 25. Which of the following is not true with regard to water? a. b. c. d. e. Water has a high heat capacity. Water has an unusually high boiling point. Water can form hydrogen bonds. Ice is more dense than liquid water. Water is a polar molecule. 26. The meniscus for water is curved upward at the edges (concave or hollow). Explain in terms of cohesion and adhesion. 27. Butter melts over a range of temperature, rather than with a sharp melting point. Butter is classified as a/an a. b. c. d. e. A. metallic crystal. covalent solid. molecular crystal. amorphous solid. ionic crystal. Kr B. Br2 C. S8 D. Ca E. K 28. Which one of the following elements would have the lowest melting point? 29. Which one of the following substances crystallizes as a covalent crystal? a. CaO b. SiO2 c. CO2 d. Pb e. KMnO4 30. Choose the response that lists the member of each of the following pairs that has the higher boiling point. (1) H2O or KI (2) HF or HI (3) Cl2 or Br2 a. b. c. d. e. H2O, HF, and Cl2 KI, HF, and Br2 KI, HI, and Br2 H2O, HI, and Cl2 KI, HF, and Cl2 Page 5