Chemistry 122 (Tyvoll) Fall 2005 PRACTICE EXAMINATION I Possibly Useful Information: 1 atm = 14.70 lb/in 2 = 101.325 kpa 1 atm = 101,325 N/m 2 = 760 mmg 1 atm = 101,325 Pa = 1.01325 bar 1 atm = 1013.25 mb 1 atm = 1.01325 bar 1 mile = 1.609 km 1 league = 2.60 miles R = 0.0821 L atm mol K R=8.314 J/K h = 6.63 X 10-34 J s N = 6.022 X 10 23 c =3.0 x10 8 m/s
Chemistry 122 (Tyvoll) Fall 2005 PRACTICE EXAMINATION I Part I. Multiple Choice 1. Which statement is not correct? 1. A volatile liquid has a high boiling point 2. The boiling point of a liquid is the temperature at which its vapor pressure is equal to the external pressure. 3. The stronger the intermolecular forces, the higher the boiling point 4. The equilibrium vapor pressure above a liquid is independent of the volume of liquid present and the volume of vapor present 5. The vapor pressure above a liquid increases with temperature. 2. Which of the following compounds is predicted to have the highest vapor pressure at STP? 1. 2 O 4. C 6 5 N 2 2.C 4 5. C 6 12 0 6 3.C 3 O 3. Which substance requires the smallest quantity of heat to melt a 1.0-g sample? 1. 2 O 18.0 (MM, g/mol) 6.01 ( fusion, kj/mol) 2. C 6 6 78.0 (MM, g/mol) 9.87 ( fusion, kj/mol) 3. Al 27.0 MM, g/mol) 10.71 ( fusion,kj/trol) 4. I 2 253.8 (MM, g/mol) 15.52 ( fusion,kj/mol) 5. All of the above require the same heat to melt a 1.0-g sample. 4. In which substance would the dispersion forces be greatest? 1. 2 4. Br 2 2. F 2 5. I 2 3.C1 2 5. Which would have the lowest boiling point? 1. CS 2 4.I 2 2. CCl 4 5.CBr 4 3. Cl 2 6. Which of the following substances would exhibit dipole-dipole intermolecular forces? 1. BCl 2 4. Cl 2 2. CF 4 5.N 3 3. CO 2
7. Which idea is incorrect? 1. Dispersion forces are present in all molecular substances. 2. The greater the dipole moment, the stronger the dipole-dipole forces. 3. The polarizability of elongated molecules is greater than tint of compact, more spherical molecules. 4. Polar molecules always have higher boiling points than nonpolar molecules. 5. ydrogen bonding leads to the strongest intermolecular forces. 8. Above the critical point for water (374 0 C and 218 atmospheres), 1. water exists only as a supercritical fluid 2. water can only be liquefied by increasing the pressure above 218 atmospheres 3. water cannot be liquefied, no matter how much pressure is applied 4. water exists only as a solid 5. water exists only as a liquid 9. What is the percent by mass of a solution made by dissolving 55.0 g KCl in 125 g water? 1. 30.6 4.56.0 2. 55.0 5.44.0 3. 68.8 10. What is the mole fraction of biphenyl, C l2 10, in a solution prepared by dissolving 22.5 g C l2 10 (s) in 285 g of benzene, C 6 6 (l)? 1. 0.0732 4.0.50 2. 0.0384 5. 0.0789 3. 0.0400 11. What mass of phenol, C 6 5 O, (FW = 94.11) must be dissolved in 25.0 g of naphthalene to produce a solution that is 0.22 m in phenol? 1. 5.6 g 4.2.2 g 2. 0.52 g 5.2.7 g 3.0.83 g 12. Calculate the molarity of a solution containing 40.0 g glucose (C 6 12 0 6, 180.0 g/mol) in enough liquid ethanol (C 2 5 O, 46.0 g/mol) to make 40.0 ml of solution. 1.0.100M 4. 5.56 M 2. 0.0900 M 5. 2.22 M 3.0.222 M
13. Which statement is incorrect? 1. When 40.0 ml of ethanol and 60.0 ml of water are mixed, the volume of the mixture is 100.0 ml. 2. When ethanol and water are mixed, the solution warms slightly. Therefore, the solution process is exothermic. 3. Ideal solutions form when the intermolecular forces of the solvent and solute are similar. 4. For an ideal solution, the of solution is zero. 5. When an ionic compound dissolves in water, the positive and negative ions separate from each other. 14. Which of the following hypothetical steps is predicted to be exothermic? 1. pure solvent separated solvent molecules 2. pure solute separated solute molecules 3. separated solvent and solute molecules solution 4. pure solvent and pure solute heterogeneous mixture 5. not enough information provided to answer this question 15. Which statement is correct? 1. A saturated solution contains a high concentration of solute. 2. A saturated solution involves a dynamic equilibrium between dissolving and crystallization. 3. The solubility of solids always increases with temperature. 4. The solubility of a gas usually increases with temperature. 5. A supersaturated solution involves a dynamic equilibrium between solute and solution.
Part II - Problems SOW ALL WORK! 1. (5 points) Part II. Completion and Short Answer. Consider the phase diagram shown at the right. Identify the solid, liquid and vapor phase regions on the actual diagram and then the processes represented by each of the following tie lines: AO OB OC 2. (10 points) Melting Points and boiling points. (a) Consider the following elements and compounds: LiBr, CO, CaO, C 3 O Arrange these substances in order of increasing melting point. < < < Explain your reasoning as completely but as concisely as possible (b) Compounds A, B, C and D (all of whose molecular structures have two carbon atoms) have the following boiling points: A, 141 0 C; B, -42.1 0 C; C, 82.4 0 C; and D, 54.5 0 C. The structures of these four compounds are shown below; identify the compounds by placing the correct letter (A, B, C or D) in the blank beneath the structure: C 3 C 2 C 3 C 3 C 2 CO C 3 C 2 O-C(=O)- C 3 C 2 C(=O)-O Explain your reasoning as completely but as concisely as possible.
3. (10 points) The molar heat of vaporization of methanol (C 3 O) is 38.0 kj/mol at 25 c. ow many joules (J) are required to convert exactly 1.00 kg of methanol (32.04 g/mol) from liquid to vapor? You must show all work for credit or partial credit!
4. (10 points) When 50.00 g of sorbitol, a molecular compound sometimes used as a sugar substitute, were dissolved in exactly 100.0 g of water, the boiling point of the water was raised from 100.000 0 C to 101.406 0 C. If K b = 0.512 0 C/molal for water, (a) calculate the molality of the solution (Show all work for credit!) (b) calculate the molar mass of sorbitol
5. (10 points) ydrogen bonds can form between (a) water molecules and acetic acid molecules and between (b) water molecules and ethanol molecules. Draw all the water molecules that can hydrogen bond to an acetic acid molecule and all the water molecules that can hydrogen bond to an ethanol molecule (two pictures). O C C O C C O acetic acid ethanol Based on your drawings, which should have the higher water solubility (affinity), acetic acid or ethanol?
6. (10 points) In a certain experiment, 144 mg of aspartame, an artificial sweetener, were dissolved in water and diluted to a final volume of exactly 25.00 ml. The osmotic pressure (Π), measured at 25 C, was 364 mmg. Use these data to calculate the molar mass (M) of aspartame.