Chem 1412 Su06 Exam 1

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1 Chem 1412 Su06 Exam 1 Student: 1. A sample of octane in equilibrium with its vapor in a closed 1.0-L container has a vapor pressure of 50.0 torr at 45 C. The container's volume is increased to 2.0 L at constant temperature and the liquid/vapor equilibrium is reestablished. What is the vapor pressure? A.> 50.0 torr B.50.0 torr C.25.0 torr D.The mass of the octane vapor is needed to calculate the vapor pressure. E.The external pressure is needed to calculate the vapor pressure. 2. Which one of the following quantities is generally not obtainable from a single heating or cooling curve of a substance, measured at atmospheric pressure? A.melting point B.boiling point C.triple point D.heat of fusion E.heat of vaporization 3. The phase diagram for xenon has a solid-liquid curve with a positive slope. Which of the following is true? A.Solid xenon has a higher density than liquid xenon. B.Solid xenon has the same density as liquid xenon. C.The phase diagram cannot be used to predict which phase of xenon is denser. D.Freezing xenon is an endothermic process. E.None of these statements is true. 1

4. Liquid ammonia (boiling point = -33.4 C) can be used as a refrigerant and heat transfer fluid. How much energy is needed to heat 25.0 g of NH 3 (l) from -65.0 C to -12.0 C? A.5.5 kj B.6.3 kj C.

2 4. Liquid ammonia (boiling point = C) can be used as a refrigerant and heat transfer fluid. How much energy is needed to heat 25.0 g of NH 3 (l) from C to C? A.5.5 kj B.6.3 kj C.39 kj D.340 kj E.590 kj 5. Octane has a vapor pressure of 40. torr at 45.1 C and 400. torr at C. What is its heat of vaporization? A.39.0 kj/mol B.46.0 kj/mol C.590 kj/mol D.710 kj/mol E.none of these choices is correct 2

3 6. Consider the following phase diagram and identify the process occurring as one goes from point C to point D. A.increasing temperature with a phase change from solid to liquid B.increasing temperature with a phase change from solid to vapor C.increasing temperature with a phase change from liquid to vapor D.increasing temperature with no phase change E.increasing temperature beyond the critical point 7. Examine the following phase diagram and determine what phase exists at point F. A.vapor + liquid B.vapor C.liquid D.solid E.supercritical fluid 3

4 8. Examine the following phase diagram and identify the feature represented by point A. A.melting point B.critical point C.triple point D.sublimation point E.boiling point 9. Ammonia's unusually high melting point is the result of A.dipole-dipole forces. B.London dispersion forces. C.hydrogen bonding. D.covalent bonding. E.ionic bonding. 10. When the electron cloud of a molecule is easily distorted, the molecule has a high. A.polarity B.polarizability C.dipole moment D.van der Waals radius E.compressibility 4

5 11. The strongest intermolecular interactions between pentane (C 5 H 12 ) molecules arise from A.dipole-dipole forces. B.London dispersion forces. C.hydrogen bonding. D.ion-dipole interactions. E.carbon-carbon bonds. 12. The strongest intermolecular interactions between hydrogen sulfide (H 2 S) molecules arise from A.dipole-dipole forces. B.London dispersion forces. C.hydrogen bonding. D.ion-dipole interactions. E.disulfide linkages. 13. Which of the following should have the highest boiling point? A.CF 4 B.CCl 4 C.CBr 4 D.CI 4 E.CH Which of the following liquid substances would you expect to have the lowest surface tension? A.Pb B.CH 3 OCH 3 C.HOCH 2 CH 2 OH D.H 2 O E.CH 3 CH 2 OH 15. A metal such as chromium in the body-centered cubic lattice will have atom(s) per unit cell. A.1 B.2 C.3 D.4 E.9 5

6 16. A cubic unit cell has an edge length of 400. pm. The length of its body diagonal (internal diagonal) in pm is therefore A.512 B.566 C.631 D.693 E When two pure substances are mixed to form a solution A.heat is released. B.heat is absorbed. C.there is an increase in entropy. D.there is a decrease in entropy. E.entropy is conserved. 18. A solution of potassium hydroxide is in equilibrium with undissolved solute at 45 C. What will happen if the temperature is raised to 50 C? ( H soln = kj/mol) A.The mass of dissolved KOH will increase. B.The mass of dissolved KOH will decrease. C.The mass of dissolved KOH will be unchanged. D.The mass of water in the solution will increase. E.More information is needed in order to make a reliable prediction. 19. The Henry's Law constant (k) for carbon monoxide in water at 25 C is mol/(l atm). How many grams of CO will dissolve in 1.00 L of water if the partial pressure of CO is 2.75 atm? A g B g C g D g E.none of these choices is correct 6

7 20. For a given solution, which of the following concentration values will change as temperature changes? A.mass percent B.molality C.mole fraction D.molarity E.none of these choices is correct 21. Calculate the molarity of a solution prepared by diluting 1.85 L of 6.5 M KOH to 11.0 L. A.0.28 M B.0.91 M C.1.1 M D.3.1 M E.3.9 M 22. What is the molality of a solution prepared by dissolving 86.9 g of diethyl ether, C 4 H 10 O, in 425 g of benzene, C 6 H 6? A m B m C.2.01 m D.2.76 m E.none of these choices is correct 23. The solubility of the oxidizing agent potassium permanganate is 7.1 g per g of water at 25 C. What is the mole fraction of potassium permanganate in this solution? A B C D.0.45 E

8 24. Aqueous ammonia is commercially available in a solution that is 28% (w/w) ammonia. What is the mole fraction of ammonia in such a solution? A B C D.0.24 E Colligative properties depend on A.the chemical properties of the solute. B.the chemical properties of the solvent. C.the masses of the individual ions. D.the molar mass of the solute. E.the number of particles dissolved. 26. From the following list of aqueous solutions and water, select the one with the highest boiling point. A.1.0 M KNO 3 B.0.75 M NaCl C.0.75 M CuCl 2 D.2.0 M C 12 H 22 O 11 (sucrose) E.pure water 27. Select the strongest electrolyte from the following set. A.CH 3 CH 2 OH, ethanol B.LiNO 3 C.C 6 H 12 O 6, glucose D.CCl 4 E.HF 28. Calculate the vapor pressure of a solution prepared by dissolving mol of a non-volatile solute in 275 g of hexane ( = g/mol) at 49.6 C. P hexane = torr at 49.6 C. A.54 torr B.154 torr C.246 torr D.346 torr E.400. torr 8

9 29. Determine the freezing point of a solution which contains 0.31 mol of sucrose in 175 g of water. K f = C/m A.3.3 C B.1.1 C C.0.0 C D.-1.1 C E.-3.3 C 30. Barbiturates are synthetic drugs used as sedatives and hypnotics. Barbital ( = g/mol) is one of the simplest of these drugs. What is the boiling point of a solution prepared by dissolving 42.5 g of barbital in 825 g of acetic acid? K b = 3.07 C/m, boiling point of pure acetic acid = C A C B C C C D C E.>120 C 31. Cinnamaldehyde ( = g/mol) is used as a flavoring agent. What mass of cinnamaldehyde must be added to 175 g of ethanol to give a solution whose boiling point is 82.7 C? K b = 1.22 C/m, boiling point of pure ethanol = 78.5 C A.62.4 g B.67.8 g C.76.2 g D.78.5 g E.79.6 g 32. Human blood has a molar concentration of solutes of 0.30 M. What is the osmotic pressure of blood at 25 C? A atm B.0.62 atm C.6.8 atm D.7.3 atm E.>10. atm 9

10 Chem 1412 Su06 Exam 1 Key 1. (p. 431) B 2. (p. Sec. 12.2) C 3. (p. 435) A 4. (p. Sec. 12.2) C 5. (p. 432) A 6. (p. 435) B 7. (p. 435) B 8. (p. 435) C 9. (p. Sec. 12.3) C 10. (p. 440) B 11. (p. Sec. 12.3) B 12. (p. Sec. 12.3) A 13. (p. Sec. 12.3) D 14. (p. 444) B 15. (p. 451) B 16. (p. Sec. 12.6) D 17. (p. Sec. 13.3) C 18. (p. 508) B 19. (p. 510) D 20. (p. Sec. 13.5) D 21. (p. 510) C 22. (p. 511) D 23. (p. 514) A 1

11 24. (p. 514) E 25. (p. 515) E 26. (p. Sec. 13.6) C 27. (p. Sec. 13.6) B 28. (p. 516) D 29. (p. 519) E 30. (p. 519) D 31. (p. 519) E 32. (p. 520) D 2

12 Chem 1412 Su06 Exam 1 Summary Category # of Questions Difficulty: E 14 Difficulty: H 2 Difficulty: M 16 Silberberg Intermolecular

Chem 1046 February 27, 2001 Test #2

Chem 1046 February 27, 2001 Test #2 1. A sample of octane in equilibrium with its vapor in a closed 1.0-L container has a vapor pressure of 50.0 torr at 45 C. The container s volume is decreased to 0.50