CHEMISTRY 123-02 Midterm #2 October 26, 2004 The total number of points in this exam is 100. The total exam time is 50 min. Good luck! PART I: MULTIPLE CHOICE (Each multiple choice question has a 2-point value!!) 1. Which compound will not dissolve in water in large amounts? a. KNO 3 b. NH 4 Cl c. Ca(OH) 2 2. Which compound will dissolve in water in large amounts? a. AgCl b. Al(OH) 3 c. Na 2 SO 4 d. AgCl e. Ag 2 SO 4 d. BaSO 4 e. MgS 3. Which statement about the reaction below is true, given large amounts of reactants? Pb(NO 3 ) 2 + Na 2 SO 4 PbSO 4 + 2NaNO 3 a. PbSO 4 is insoluble in water and will precipitate. b. NaNO 3 is insoluble in water and will precipitate. c. Pb(NO 3 ) 2 is insoluble in water and no reaction will occur. d. Both NaNO 3 and PbSO 4 are insoluble in water and will precipitate. e. All compounds in the reaction are soluble in water and no reaction occurs. 4. What is the net ionic equation for the reaction of AlCl 3 and NaOH? a. Na + + Cl - NaCl b. Al + + OH - AlOH c. Al 3+ + 3OH - Al(OH) 3 d. Al 3+ + OH 3- AlOH e. Na 3+ + 3Cl - NaCl 3 5. What is the correct formula for the hydronium ion? a. OH - b. H 3 O + c. H + 6. What is the correct formula for the hydroxide ion? a. H 3 O + b. OH - c. + NH 4 d. H - e. NH 4 + d. H + e. H - 7. Which statement about strong acids is false? a. Strong acids are strong electrolytes. b. Strong acids are very concentrated. c. Strong acids are almost entirely converted to ions when dissolved in water. d. Nitric acid is a strong acid. e. Strong acids react with carbonates to produce CO 2 (g). 8. All of the following are strong electrolytes except: a. CH 3 COOH. b. H 2 SO 4. c. HNO 3. 9. Which of the following is a nonelectrolyte? a. Ba(OH) 2 b. CsBr c. KI d. HBr. e. NaOH. d. HBr e. CBr 4
10. Which statement about neutralization reactions is false? a. The reaction of a strong base with a strong acid is an example of a neutralization reaction. b. Neutralization reactions produce salts. c. The net ionic equation for a neutralization reaction shows the formation of hydrogen gas. d. Weak acids can neutralize strong bases. e. Neutralization reactions produce water. 11. What species is the reducing agent in the reaction below? Zn(s) + CuSO 4 (aq) ZnSO 4 (aq) + Cu(s) a. Zn b. Cu 2+ c. CuSO 4 12. Which of the following is a reducing agent? a. I 2 b. Na c. O 2 13. Which substance is oxidized in the reaction below? a. CO b. S c. Na 2 S 14. What is the oxidation number of Mg in MgH 2? a. -1 b. +1 c. 0 15. What is the oxidation number of O in O 2? a. -1 b. +1 c. 0 16. What is the oxidation number of P in PO 3-3? a. +5 b. +3 c. -2 d. Zn 2+ e. 2- SO 4 d. F 2 e. Br 2 Na 2 SO 4 + 4 C Na 2 S + 4CO d. Na 2 SO 4 e. none of the above d. +2 e. -2 d. +2 e. -2 d. -3 e. -5 17. Which reaction will not occur as suggested? a. Al (s) + SnCl 2 (aq) AlCl 3 (aq) + Sn(s) b. H 2 (g) + AgNO 3 (aq) HNO 3 (aq) + Ag(s) c. Mg(s) + CuSO 4 (aq) Cu(s) + MgSO 4 (aq) d. Mg(s) + CaSO 4 (aq) MgSO 4 (aq) + Ca(s) e. Ba (s) + HCl(aq) BaCl 2 (aq) + H 2 (g) 18. A 50.0 ml sample of 0.108 M H 2 SO 4 is diluted to 250.0 ml. What is its new molarity? a. 0.0216 M b. 0.108 M c. 0.184 M d. 0.461 M e. 0.542 M 19. Which of the methods described below will yield 500 ml of a 0.100 M KMnO 4 solution? a. Add exactly 500 ml of water to 7.90 g of KMnO 4. b. Add exactly 500 ml of water to KMnO 4. c. Dissolve 7.90 g of KMnO 4 in water and dilute to exactly 500 ml. d. Dissolve 15.8 g KMnO 4 in water and dilute to exactly 500 ml. e. Dilute 220 ml of 1.00 M KMnO 4 to exactly 500 ml.
20. If heat is transferred from the system to the surroundings then a. q system is positive b. q system is negative c. The system is doing work d. The surroundings are doing work e. Both a and c. 21. If a 10.0 g sample of each substance below has 250 J applied to it, which substance will have the greatest increase in temperature? a. Iron (specific heat = 0.46 J/g) d. Aluminum (specific heat = 0.92 J/g) b. Water (specific heat = 4.184 J/g) e. Not enough information to determine. c. Copper (specific heat = 0.39 J/g) 22. What is the molar heat capacity of aluminum (specific heat = 0.92 J g -1 C -1 )? a. 0.034 J mol -1 C -1 d. 120 J mol -1 C -1 b. 24.8 J mol -1 C -1 e. 1.5 10 25 J mol -1 C -1 c. 29.3 J mol -1 C -1 23. Which process is exothermic? a. Freezing rain drops b. Evaporating alcohol c. Defrosting frozen food 24. Which term refers to a quantity of heat transferred at constant pressure? a. Work b. Specific heat capacity c. Expansion d. Warming milk e. Subliming dry ice d. Entropy e. Enthalpy 25. Which statement is true? a. A positive change in enthalpy occurs with exothermic processes. b. A negative change in enthalpy occurs with exothermic processes. c. A positive change in enthalpy occurs when work is done on the surroundings. d. A negative change in enthalpy occurs when work is done by the system. e. A positive change in enthalpy occurs when a process is endothermic and does work on the surroundings. 26. When does an endothermic reaction occur? a. When bonds are broken b. When bonds are formed c. When the energy of bonds breaking is greater than the energy of bonds formed d. When the energy of bonds breaking is less than the energy of bonds formed e. When stronger bonds are formed and weaker bonds are broken 27. Based on the equation below, which statement is incorrect? 2H 2 (g) + O 2 (g) 2H 2 O(l) H = - 571.7 kj a. The value of 571.1 kj applies to one mole of liquid water. b. Per half mole of O 2, H -285.8 kj. c. If the state of water changes from the liquid state to the gas state, the value for H no longer applies. d. If the equation above is divided by 2, H = - 285.8 kj. e. If the equation above is reversed, H = + 571.1 kj. PART II: SHORT ANSWER (Each short answer question has a 1-point value!!) 28. Molarity is a unit of solution concentration expressed in moles per. 29. When an element is, it loses electrons. 30. A neutralization reaction involves the reaction of a(n) with a(n). 31. A chemical equation without the spectator ions is called a ionic equation.
32. In an endothermic reaction, heat is transferred from the to the. 33. Energy of motion is called. 34. The quantity of energy required to increase the temperature of one gram of a sample by 1 C is called the. 35. In a(n) reaction, the energy of bond breaking is greater than the energy of bond making. 36. Enthalpy change is equal to heat transfer at constant. 37. According to the First Law of Thermodynamics, the total of the universe is constant. PART III: CHEMICAL REACTIONS 38. (12 pts) Write (clearly and distinctly) the complete and net ionic equations for each of the following reactions. If no reaction occurs, write NR. Li 2 CO 3 (s) + HNO 3 (aq) K 3 PO 4 (aq) + CuCl 2 (aq) LiOH(aq) + HCN(aq) 39. (9 pts) Find which of the equations below represent redox reactions. Indicate the element that is reduced and the element that is oxidized. Write their oxidation numbers before and after the reaction. 3 HNO 2 (aq) HNO 3 (aq) + H 2 O(l) + NO(g) 2HIO 3 (s) I 2 O 5 (s) + H 2 O(l) Cl 2 (g) + 2NaI(s) 2NaCl(s) + I 2 (s) 40. (4 pts) For each of the following displacement reactions, predict whether the process will occur from left to right or from right to left. a. Al 3+ (aq) + Cr (s) or Cr 3+ (aq) + Al (s) b. 2 H + (aq) + Pb (s) or Pb 2+ (aq) + H 2 (g) PART IV: CALCULATION PROBLEMS (Show your work in its entirety. Do not provide just a single number!). 41. (6 pts) 100.0 ml of 0.200 M CsOH and 50.0 ml of 0.400 M HCl were mixed in a calorimeter. The starting solutions temperature was 22.50 o C and the final temperature after mixing was 24.28 o C. Assume density for the final solution of 1.00 g/ml and specific heat of the final solution of 4.184 J/g. o C. Write the complete thermochemical equation for the process (Hint: You have to determine limiting reactant!!).
PART V: CONCEPTS 42. When 1.0 g of certain substance is heated, the following graph results (S = solid; L = liquid; V = vapor): 350 300 250 V T [oc] 200 150 L 100 S 50 0 0 100 200 300 400 500 600 700 800 q [J] Answer the following questions: (1 pts) Which quantity has larger value: Heat of vaporization or heat of fusion? (1 pts) Calculate the heat change during condensation of 2.0 g of V at 200 o C; (1 pts) Which has larger specific heat capacity: S or L? (2 pts) What quantity of heat is required to raise the temperature of 5.0 g of L by 10 o C?