CHEM-112-01 Spring 2012 Name: Class: Date: 1. Record your name and ID number on the scantron form. 2. Record the test ID letter in the top right box of the scantron form. 3. Record all of your answers on the scantron form. DO NOT wait until the end to do this! 4. Remain seated until the period is over. 5. Pass the scantron form to the center. 6. Take your exam with you. You have 50 minutes. GOOD LUCK! Exam 2 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. What is the ID letter of your exam? Record this for question 1. a. A d. D b. B e. E c. C 2. If 355 g of ethanol (C 2 H 5 OH) is added to 645 g of water, what is the molality of the ethanol? a. 0.550 m b. 7.71 m c. 11.9 m d. 21.7 m e. 55.0 m 3. The heat of formation of NaCl(s) is 411.1 kj/mol and the heat of formation of NaCl(aq, 1 m) is 407.3 kj/mol. Determine the heat of solution of NaCl. Will the solution temperature increase or decrease when NaCl is dissolved in water? a. 3.8 kj/mol; increase b. +3.8 kj/mol; increase c. +3.8 kj/mol; decrease d. +818.4 kj/mol; increase e. 818.4 kj/mol; decrease 4. Which action(s) will increase the equilibrium concentration of a non-reacting gas in water? 1. decreasing the temperature of the water 2. increasing the volume of water 3. decreasing the pressure of the gas above the liquid a. 1 only b. 2 only c. 3 only d. 1 and 3 e. 1, 2, and 3 1
Name: 5. Arrange PH 3, AsH 3, and SbH 3 in order from lowest to highest boiling point. a. SbH 3 < AsH 3 < PH 3 b. PH 3 < AsH 3 < SbH 3 c. PH 3 < SbH 3 < AsH 3 d. AsH 3 < SbH 3 < PH 3 e. SbH 3 < PH 3 < AsH 3 6. What is the freezing point of a solution containing 3.10 grams benzene (molar mass = 78.11 g/mol) dissolved in 32.0 grams paradichlorobenzene? The freezing point of pure paradichlorobenzene is 53.0 C and the freezing point depression constant, K fp, is 7.10 C/m. a. 44.2 C b. 51.8 C c. 52.3 C d. 54.2 C e. 61.8 C 7. What is the H 3 O + concentration of an aqueous solution with a ph of 8.77? a. 1.7 10 9 M b. 5.9 10 6 M c. 1.6 10 4 M d. 5.23 M e. 5.9 10 8 M 8. As pure molecular solids, which of the following exhibits dipole-dipole intermolecular forces: PBr 3, SO 2, I 2, and CO 2? a. PBr 3 only b. PBr 3 and SO 2 c. SO 2 and CO 2 d. I 2 and CO 2 e. PBr 3, SO 2, and I 2 9. Ethanol has an enthalpy of vaporization of 42.3 kj/mol. The compound has a vapor pressure of 1.00 atm at 78.3 C. At what temperature is the vapor pressure equal to 0.500 atm? (R = 8.314 J/K mol) a. 96.2 C b. 7.19 C c. 36.0 C d. 62.2 C e. 281 C 10. Normal boiling point is defined as a. the temperature at which the vapor pressure of a liquid equals 1 atm. b. the pressure at which any liquid boils at 373.15 K. c. the temperature at which water always boils. d. the pressure of a gas when its temperature reaches 273.15 K. e. the temperature at which the enthalpy of vaporization equals 100.0 kj/mol. 2
Name: 11. What is the ph of 0.25 M aqueous acetic acid? (K a of CH 3 CO 2 H = 1.8 10 5 ) a. 0.60 b. 2.67 c. 4.74 d. 5.35 e. 9.26 12. Which of the following statements is/are CORRECT? 1. If the intermolecular forces in a liquid decrease, the normal boiling point of the liquid decreases. 2. If the surface area of a liquid increases, the equilibrium vapor pressure of the liquid increases. 3. If the temperature of a liquid decreases, the equilibrium vapor pressure increases. a. 1 only b. 2 only c. 3 only d. 1 and 2 e. 1, 2, and 3 13. What is the ph of 4.4 10 4 M KOH(aq) at 25 C? (K w = 1.0 10 14 ) a. 3.36 b. 3.36 c. 6.27 d. 7.73 e. 10.64 14. Which equation depicts hydrocyanic acid, HCN, behaving as a Brønsted-Lowry acid in water? a. HCN(aq) + OH (aq) OCN (aq) + H 2 (g) b. HCN(aq) + H 3 O + (aq) H 2 CN + (aq) + H 2 O( ) c. HCN(aq) + H 2 O( ) CN (aq) + H 3 O + (aq) d. CN (aq) + H 3 O + (aq) HCN(aq) + H 2 O( ) e. CN (aq) + H 2 O( ) OCN (aq) + H 2 (s) 15. Ideally, colligative properties depend only on the a. concentration of solute particles in a solution. b. molar masses of the solute particles in a solution. c. density of a solution. d. hydrated radii of the molecules or ions dissolved in a solution. e. partial pressure of the gases above the surface of a solution. 3
Name: 16. At its boiling point of 34.0 C, 6.33 kj of heat is required to vaporize 22.0 g of chlorine (Cl 2 ). What is the molar enthalpy of vaporization of chlorine? a. 0.0893 kj/mol b. 0.286 kj/mol c. 1.96 kj/mol d. 20.4 kj/mol e. 139 kj/mol 17. In class I did a demonstration that yielded a sodium acetate (CH 3 CO 2 Na) tower. This demonstrated: a. a supersaturated solution d. volatility of a compound b. the vapor pressure difference e. none of the above c. acid and base chemistry 18. Which of the following substances is never a Brønsted-Lowry base in an aqueous solution? a. potassium hydroxide, NaOH(g) b. sodium dihydrogen phosphate, NaH 2 PO 4 (s) c. sodium phosphate, Na 3 PO 4 (s) d. ammonium chloride, NH 4 Cl(g) e. sodium bicarbonate, NaHCO 3 (s) 19. What is the equilibrium partial pressure of water vapor above a mixture of 89 g H 2 O and 156.0 g HOCH 2 CH 2 OH at 35 C. The partial pressure of pure water at 35.0 C is 42.2 mm Hg. Assume ideal behavior for the solution. a. 0.730 Hg b. 27.96 mm Hg c. 56.0 mm Hg d. 27.1 mm Hg e. 58.0 mm Hg 20. List all the intermolecular forces present in pure acetone. a. hydrogen bonding only b. dipole-dipole force only c. dipole-dipole force and induced dipole/induced dipole force d. hydrogen bonding and induced dipole/induced dipole force e. hydrogen bonding, dipole-dipole force, and induced dipole/induced dipole force 21. Place the following cations in order from lowest to highest hydration enthalpy. a. Na + < Rb + < H + b. Rb + < H + < Na + c. Rb + < Na + < H + d. H + < Na + < Rb + e. H + < Rb + < Na + 4
Name: 22. Which of the following chemical equations corresponds to the second acid ionization constant, K a2, for oxalic acid (H 2 C 2 O 4 )? a. H 2 C 2 O 4 (aq) + H 3 O + (aq) HC 2 O 4- (aq) + H 2 O( ) b. HC 2 O 4- (aq) + H 3 O + (aq) H 2 C 2 O 4 (aq) + H 2 O( ) c. HC 2 O 4- (aq) + H 2 O( ) H 2 C 2 O 4 (aq) + HO - ( ) d. HC 2 O 4- (aq) + H 2 O( ) C 2 O 2-4 (aq) + H 3 O + (aq) e. H 2 C 2 O 4 (aq) + H 2 O( ) HC 2 O 4- (aq) + H 3 O + (aq) 23. Which one of the following molecules will exhibit dipole-dipole intermolecular forces as a pure liquid? a. C 2 H 2 b. SO 3 c. CO 2 d. F 2 e. NO 2 24. What is the mole fraction of calcium chloride in 4.47 m CaCl 2 (aq)? The molar mass of CaCl 2 is 111.0 g/mol and the molar mass of water is 18.02 g/mol. a. 0.0745 b. 0.0805 c. 0.199 d. 0.496 e. 0.860 25. Ammonium ion has a pk a value of 9.25. What is the value of pk b for ammonia? a. 5.6 10 10 b. 1.8 10 5 c. 0.108 d. 0.75 e. 4.75 26. Which of the following acids has the strongest conjugate base in an aqueous solution? a. acetic acid, K a = 1.8 10 5 b. hydrocyanic acid, K a = 4.0 10 10 c. hydrogen sulfite ion, K a = 6.2 10 8 d. nitrous acid, K a = 4.5 10 4 e. phosphoric acid, K a = 7.5 10 3 5
Exam 2 Answer Section MULTIPLE CHOICE 1. ANS: A PTS: 1 2. ANS: C PTS: 1 TOP: 14.1 Units of Concentration 3. ANS: C PTS: 1 TOP: 14.2 The Solution Process 4. ANS: A PTS: 1 TOP: 14.3 Factors Affecting Solubility: Pressure and Temperature 5. ANS: B PTS: 1 TOP: 12.2 Intermolecular Forces Involving Polar Molecules 6. ANS: A PTS: 1 TOP: 14.4 Colligative Properties 7. ANS: A PTS: 1 TOP: 17.3 Water and the ph Scale 8. ANS: B PTS: 1 TOP: 12.2 Intermolecular Forces Involving Polar Molecules 9. ANS: D PTS: 1 TOP: 12.4 Properties of Liquids 10. ANS: A PTS: 1 TOP: 12.4 Properties of Liquids 11. ANS: B PTS: 1 TOP: 17.7 Calculations with Equilibrium Constants 12. ANS: A PTS: 1 TOP: 12.4 Properties of Liquids 13. ANS: E PTS: 1 TOP: 17.3 Water and the ph Scale 14. ANS: C PTS: 1 TOP: 17.2 The Brønsted-Lowry concepts of Acids and Bases 15. ANS: A PTS: 1 TOP: 14.4 Colligative Properties 16. ANS: D PTS: 1 TOP: 12.4 Properties of Liquids 17. ANS: A PTS: 1 18. ANS: D PTS: 1 TOP: 17.2 The Brønsted-Lowry concepts of Acids and Bases 19. ANS: B PTS: 1 TOP: 14.4 Colligative Properties 20. ANS: C PTS: 1 TOP: 12.3 Interactions Involving Nonpolar Molecules 21. ANS: C PTS: 1 TOP: 12.2 Intermolecular Forces Involving Polar Molecules 22. ANS: D PTS: 1 TOP: 17.4 Equilibrium Constants for Acids and Bases 23. ANS: E PTS: 1 TOP: 12.2 Intermolecular Forces Involving Polar Molecules 24. ANS: A PTS: 1 TOP: 14.1 Units of Concentration 25. ANS: E PTS: 1 TOP: 17.4 Equilibrium Constants for Acids and Bases 26. ANS: B PTS: 1 TOP: 17.4 Equilibrium Constants for Acids and Bases 1