课程名称︰ 普通化学甲下 课程性质︰ 必修 课程教师︰ 佘瑞琳 开课学院： 开课系所︰ 农化、地质、大气 考试日期（年月日）︰ 101/4/11 考试时限（分钟）： 120 mins 是否需发放奖励金： yes （如未明确表示，则不予发放） 试题 : General Chemistry 100-2 A Midterm-Exam 2012/4/11 Gas constant: R = 8.314 J/mol-K = 0.082 L-atm/mol-K I.Multiple choices questions (2 points per question, 20%) 1. Choose the correct statement. (a) If you compare two reactions with similar collision factors, the one with the larger activation energy will be faster. (b) A reaction that has a small rate constant must have a small frequency factor. (c) Increasing the reaction temperature increase the fraction of successful collisions between reactants. (d) Exothermic reactions are faster than endothermic reactions. 2. Base on the reaction profile for reaction A → D, choose the correct statement. (a) There are two intermediates. (b) There are two transitions states. (c) Step B → C is the fastest. (d) The reaction A → D is endothermic. potential energy ↑ │ │ │ │ │ ∕﹨ │ ∕ ﹨ │ ∕ ﹨╱﹨ │ ∕ C ﹨ │ ∕╲∕ ﹨ │ ∕ B ﹨＿＿ │A ∕ D │── │ └─────────────────→ Reaction prograss 3. Given the reactions, HF(aq) → H+ (aq) + F- (aq) Kc = 6.8 * 10^(-4) H2C2O4(aq) → 2H+ (aq) + C204(2-)(aq) Kc = 3.8 * 10^(-6) determine the value of Kc for the reaction 2HF(aq) + C204(2-)(aq) → 2F- (aq) + H2C2O4 (aq) (a) 2.6 * 10^(-9) (b) 0.12 (c) 8.2 (d) 1.8 * 10^2 4. Consider the equilibrium, N204 (g) → 2NO2 (g) △H = 58.0 KJ which of the following will shift the quilibrium to the right. (a) N204 is added. (b) The pressure is increased by addition of N2(g) at constant volume. (c) The volume is increased. (d) The temperature is decreased. 5. Which of the following is conjugated acid-base pair? (a) HClO4 / HClO3 (b) PH4+ / PH3 (c) H2CO3 / CO3(2-) (d) H20 / OH- 6. For the 1.0 M aqueous solutions of the following compounds, indicate the one that is acidic. (a) NH4Br (b) Pb(NO3)2 (c) Na2CO3 (d) KClO4 7. Which of these substances are more soluble in acidic solution than in basic solution: (a) CuS (s) (b) CaCO3 (s) (c) BaF2(s) (d) AgCl (s) 8. You have to prepare a pH 3.50 buffer, and you have the following 0.10 M solutions available. Which solutions would you use? (a) HF / NaF (b) HCl / NaCl (c) H3PO4 / NaH2PO4 (d) HCN / NaCN Ka(HF) = 6.8 * 10^(-4) Ka1(H3PO4) = 7.5 * 10^(-3) Ka(HCN) = 4.9 * 10^(-10) 9. A solution containing an unknown number of metal ions is treated with dilute HCl, a precipitate forms. After the precipitate is filtered off, the pH is adjusted to about 1 and H2S is bubbled in; a precipitate again forms. Which metal ions are possibly present? (a) Hg2(2+) (b) Mg(2+) (c) Fe(3+) (d) Sn(4+) 10. For the following titration, which would you expect the pH value of solution at equivalence point to be above 7? (a) Aminomethane, CH3NH2(aq), is titrated with HCl(aq). (b) HI(aq) is titrated with KOH(aq). (c) Formic acid, HCOOH(aq), is titrated with Ba(OH)2 (aq). (d) Potassium hydrogen phthalate (KHP) is titrated with NaOH (aq). II. Problems (80%) 1. The following data were measured for the reaction of nitric oxide with hydrogen: 2 NO (g) + 2 H2 (g) → N2 (g) + 2 H20 (g) Trial │ [NO] (M) │ [H2] (M) │ Initial rate (M/s) ────────────────────────── 1 │ 0.10 │ 0.10 │ 1.23 * 10^(-3) 2 │ 0.10 │ 0.20 │ 2.46 * 10^(-3) 3 │ 0.20 │ 0.10 │ 4.92 * 10^(-3) (a) Determine the rate law for this reaction. (b) Calculate the rate constant. (c) Calculate the initial rate when [NO] = 0.050 M and [H2] = 0.150 M. (6%) 2. For the oricess N205 (g) → NO2 (g) + NO3 (g) the activation energy (Ea) and overall △E are 154 KJ/mol and 136 KJ/mol, respectively. (a) Sketch the energy profile for this reaction, and label Ea and △E. (b) What is the activation energy for the reverse reaction. (6%) 3. For a gas phase reaction: 2NO(g) + Br2(g) → 2NOBr(g), the experimentally determined rate law is Rate = k[NO]^2[Br2]. Derive that the following steps are probable mechanisms. (10%) Step 1 : NO(g) + NO(g) →(k1) N2O2 (g) (fast,equilibrium) ←(k-1) Step 2 : N202(g) + Br2(g) →(k2) 2NOBr(g) (slow) 4. A 1.000-L flask is filled with 1.000 mol of H2(g) and 2.000 mol of I2(g) at 448。C. The value of the equilibrium constant Kc for the reaction at 448。C is 50.5 . H2(g) + I2(g) → 2HI(g). (a) Calculate the initial concentrations of H2(g) and I2(g). (b) Calculate the value of Kp for the reaction. (c) What are the equilibrium concentrations of H2, I2, and HI in moles per liter? (8%) 5. A student prepared a 0.10 M solutions of formic aacid (HCOOH) and found its pH at 25。C to be 2.38. (a) Calculate Ka for formic acid at this temperature. (b) Calculate the percent ionization of the acid. (c) Calculate the percent ionization of this 0.10 M formic acid in a solution containing 0.020 M sodium formate (HCOONa) (6%) 6. Predict and give the explanations whether the salt Na2HPO4 forms an acidic solution or a basic solution when dissolved in water. (4%) (For H3PO4 , Ka1 = 7.5 * 10^(-3) , Ka2 = 6.2 * 10^(-8) , Ka3 = 4.2 * 10^(-13) 7. (a) How many moles of NH4Cl must be added to 2.0 L of 0.10 M NH3 to form a buffer whose pH is 9.00 ? Assume that the addition of NH4Cl does not change the volume of the solution. (b) Determine the pH of the solution that would result from the addition of 0.020 mol HCl to the solution. Kb for NH3 is 1.8 * 10^(-5) 8. Solid silver chromate is added to pure water at 25。C, and some of the solid remains undissolved. The mixture is stirred for several days to ensure that equilibrium is achieved between the undissolved Ag2CrO4(s) and the solution. Analysis of the equilibrated solution shows that its silver ion concentration is 1.3 * 10^(-4) M. (a) Assuming that Ag2CrO4 dissociates completely in water and that here are no other important equilibria involving Ag+ or CrO4(2-) ions in the solution, calculate Ksp for this compound. ***Give the Ksp expression of Ag2CrO4 first. 9. A solution contains 1.0 * 10^(-2) M Ag+ and 2.0 * 10^(-2) M Pb(2+). When Cl- is added, both AgCl (Ksp = 1.8 * 10^(-10) ) and PbCl2 (Ksp = 1.7 * 10^(-5) ) can precipitate. (a) What concentration of Cl- is necessary to begin the precipitation of each salt? (b) Which salt precipitates first? (6%) 10. Consider CaCO3 (calcite), whose solubility product, Ksp = 4.5 * 10^(-9) M. 6% (a) Calculate the value of solubility from Ksp. (b) The reported solubility is 1.4 * 10^(-4) M. Indicate the common sources that cause the differences between the calculated and reported solubility. 11. Draw the titration curves of 0.100 M HCl and 0.100 M CH3COOH which are titrated with 0.100 M NaOH, respectively. Illustrate the differences between the titration curves. (8%) 12. 请恕略了，sorry~ (8%) --

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