NAME CHEMISTRY 102 FALL 2009 EXAM 1 FORM A SECTION 501 DR. KEENEY-KENNICUTT Directions: (1) Put your name on PART 1 and your name and signature on PART 2 of the exam where indicated. (2) Sign the Aggie Code on PART 2 of this exam. (3) Each multiple choice question is actually 2 questions on your scanning sheet. If you are sure of an answer, put the same answer down for both questions for 5 pts. If you cannot decide between two answers, put your best answer down for the first (odd) question and the other answer down for the second (even) question. If you get the first one correct you'll get 3 pts; if you get the second one correct you ll get 2 pts. If there is an ambiguous multiple choice question, use the last page to explain your answer. (4) Do NOT write on the envelope. (5) When finished, put everything in the envelope and wait to be excused. At the table, take everything out of the envelope. You can pick up the multiple choice part with the answers outside my office after 3pm. (6) There are a total of 36 questions (20 actual questions). PART 1 1&2. Which of the following statements is TRUE? (a) The ideal van t Hoff factor for sodium nitrate is 3. (b) The ideal van t Hoff factor can accurately be used for all solutes. (c) The freezing point depression is inversely proportional to i, K f and molality. (d) If i = 1, the solute is a non-electrolyte. (e) The molecular weight of a solute has no effect on the freezing point of a solution of that solute. 3&4. Water and methanol are miscible because both (1) have very different structures (2) are similar in polarity (3) have hydrogen bonding (a) 1 only (b) 2 only (c) 3 only (d) 1&2 (e) 2&3 5&6. The units of molarity are: (a) mol solute/l solution (b) g solute/kg solvent (c) g solute/g solvent (d) mol solute/kg solution (e) mol solute/kg solvent 7&8. Which of the following gives an element in its thermodynamic standard state? (a) CO 2 (g) (b) N 2 (g) (c) Kr(s) (d) Fe(l) (e) Hg(s) Keeney-Kennicutt, 2009 A1
9&10. Which of the following statements is FALSE about colligative properties? (a) The fact that water boils at a higher temperature than benzene has nothing to do with colligative properties. (b) Osmotic pressure results when the solvent molecules move from a solution of lower concentration to a solution of higher concentration. (c) Colligative properties are physical properties of solutions. (d) The boiling point of a solution of 2 m NaCl(aq) will be twice as high as the boiling point of a 1 m NaCl(aq) solution. (e) The units of the molal freezing point depression constant are o C/m. 11&12. From the table of thermodynamic data, we see that ΔHf o 298 (kj/mol) for Ag 2 O(s) is 31 kj/mol. This value is the ΔH for the following reaction: (a) 2Ag(s) + O(g) Ag 2 O(s) (b) 2Ag 2 O(s) 4Ag(s) + O 2 (g) (c) 2Ag 2 O(s) 4Ag(s) + 2O(g) (d) 4Ag(s) + O 2 (g) 2Ag 2 O(s) (e) 2Ag(s) + ½ O 2 (g) Ag 2 O(s) 13&14. Which choice gives the system with lower entropy first and the system with higher entropy second? (a) H 2 S(g) < H 2 S(s) (b) NaCl(s) < NaCl(aq) (c) CH 3 CH 2 CH 3 (g) < CH 4 (g) (d) O 2 (g) at 100 o C < O 2 at 0 o C (e) 1 mol of N 2 (g) in 10 L < 1 mol of N 2 (g) in 1 L 15&16. Consider the following reaction: A B with ΔHrxn = 100 kj and ΔSrxn = 50 J/K. We know: (a) the reaction is exothermic and becoming more ordered (b) the reaction is exothermic and becoming less ordered (c) the reaction is endothermic and becoming more ordered (d) the reaction is endothermic and becoming less ordered (e) it is impossible to know 17&18. Which statement is FALSE? (a) The entropy of a pure perfect crystalline substance is 0 at 0 K. (b) In a spontaneous reaction, the disorder of the universe increases. (c) When heat is released to the surroundings, ΔS surr becomes more positive. (d) S surr = H system /T(in K) (e) As the temperature of a substance increases, its entropy decreases. Keeney-Kennicutt, 2009 A2
19&20. Consider the condensing of water: H 2 O(g) H 2 O(l). Which of the following statements is CORRECT? (a) The system is becoming more disordered. (b) Entropy is increasing. (c) The process is exothermic and releases heat to the surroundings. (d) The process occurs spontaneously at all temperatures. (Use your common sense.) (e) At 0 o C, the system is at equilibrium. 21&22. A solution made by dissolving 25.0 g of ZnSO 4 in 150. g of water has a molality of: (a) 0.169 m (b) 0.147 m (c) 1.03 m (d) 0.875 m (e) 0.522 m 23&24. What is the entropy change of the reaction below at 298 K and 1 atm pressure? 2 Na(s) + 2 H 2 O(l) 2 NaOH(aq) + H 2 (g) S o (J/mol K) 51.0 69.91 49.8 130.6 (a) 11.6 J/K (b) +161.5 J/K (c) +59.5 J/K (d) 197 J/K (e) +24.7 J/K Keeney-Kennicutt, 2009 A3
25&26. A solution was prepared by dissolving 4.59 g sample of unknown ionic compound with a formula weight of 84.0 g/mol in 100.0 g of water. The solution boiled at 101.12 o C. One mole of the ionic compound is probably composed of how many moles of ions? (a) 1 (b) 2 (c) 3 (d) 4 (e) 5 27&28. Calculate the molarity of an MgSO 4 solution if 25.30 g of MgSO 4 (FW=120.4 g/mol) is added to 70.0 g of water. The resulting solution has a density of 1.28 g/ml. (a) 2.55 M (b) 2.82 M (c) 2.40 M (d) 2.71 M (e) 2.25 M Keeney-Kennicutt, 2009 A4
29&30. A solution containing 19.5 g of a polymer (nonelectrolyte) in 300. ml of a benzene solution has an osmotic pressure of 0.044 atm at 27 o C What is the apparent formula weight of the polymer? (a) 73,000 g/mol (b) 49,000 g/mol (c) 36,000 g/mol (d) 21,000 g/mol (e) 3,300 g/mol 31&32. The freezing point of a 0.434 m solution of the non-electrolyte, ethanol, dissolved in formic acid is 7.20 o C. The freezing point of pure formic acid is 8.40 o C. Calculate the K f for formic acid. (a) 0.54 o C/m (b) 1.19 o C/m (c) 1.44 o C/m (d) 2.18 o C/m (e) 2.76 o C/m Keeney-Kennicutt, 2009 A5
Keeney-Kennicutt, 2009 A6
CHEMISTRY 102 EXAM 1 Form A FALL 2009 Section 501 NAME PART 2 (Please Block Print) Please read and sign: On my honor, as an Aggie, I have neither given nor received unauthorized aid on this exam. (8 pts) 33. Give the name or formula to the following compounds: (a) strontium chloride (b) Cu(BrO 3 ) 2 (c) acetone (d) C 3 H 8 (2 pts) 34. Consider the diagram given on the right, relating the vapor pressure and temperature of a pure solvent, C, and a solution made from the pure solvent, D. Vapor pressure is on the (x or y) axis. Temperature lies on the (x or y) axis. 35. Consider this reaction: 2HgO(s) 2Hg(l) + O 2 (g) H rxn = +181.7 kj and S rxn = +216.5 J/K (2 pts) (a) Explain briefly why the sign of S rxn makes sense. (3 pts) (b) Calculate S surr at 25 o C and explain briefly why the sign of S surr makes sense. OVER Keeney-Kennicutt, 2009 A7
(5 pts) 36. What is the change in enthalpy (in kj) for this reaction when 10.0 g of HNO 3 (l) are produced? 3NO 2 (g) + H 2 O(l) 2HNO 3 (l) + NO(g) ΔH o f 298 (kj/mol) +33.2 285.8 174.1 +90.25 Keeney-Kennicutt, 2009 A8
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