课程名称︰普通化学甲下 课程性质︰物理系、材料系大一必带 课程教师︰金必耀 开课学院：理学院 开课系所︰化学系 考试日期（年月日）︰2019/06/21 考试时限（分钟）：120分钟 是否需发放奖励金 : 是 试题 : Final Exam Problem 1. A physician wishes to prepare a buffer solution at pH = 3.82 that if ciently resists changes in pH yet contains only small concentrations of the buffering agents. Determine which one of the following weak acids, together with its sodium salt, would probably be best to use: m-chlorobenzoic acid, Ka = 1.04e-4 ; p-chlorocinnamic acid Ka = 3.89e-5 ; 2,5-dihydroxybenzoic acid, Ka = 1.08e-3 ; or acetoacetic acid, Ka = 2.62e-4. Explain. Problem 2. Thiamine hydrochloride (vitamin B_1 hydrochloride, HC12H17ON14SCl2) is a weak acid with Ka = 3.4e-7. Suppose 3.0e-5 g of thiamine hydrochloride is disolved in 1.00 L of water. Calculate the pH if the resulting solution. (Hint: This is a sufficiently dilute solution that the autoionization of water cannot be neglected.) Problem 3. Consider the two following nitrophenol structures: OH OH ∣ ∣ ／＼ ／＼ ∣O ∣ ∣O ∣ ＼／ ＼／＼ ∣ N0_2 N0_2 p-nitrophenol m-nitrophenol Predict which will be the stronger acid. Explain your prediction. Problem 4. A Zn|Zn^{2+}||Co^{2+}|Co galvanic cell is constructed in which the standard cell potential is 0.48V. Calculate the free energy change at 25度C per gram of zinc lost at the anode, if all concentrations remain at their standard value of 1 M throughout the process. What is the maximum electrical work done by the cell on its surroundings during this experiment? Problem 5. (a.) The concentration of the electrolyte, sulfuric acid, in a lead-acid storage battery diminishes as the battery is discharged. Is a discharged battery recharged by replacing the dilute H_2SO_4 with fresh, concentrated H_2SO_4? Explain. (b.) One cold winter morning the tmperature is well below 0度F. In trying to start yout car, you run the battery down completely. Several hours later, you return to replace yout fouled spark plugs and find that the liquid in the battery has now frozen even though the air temperature is actually a bit higher that it was in the morning. Explain how this happen. Problem 6. By considering these half-reactions and their standard reduction potential, Pt^{2+} + 2e- → Pt E = 1.2 V NO3- + 4H3O+ + 3e- → NO + 6H20 E = 0.96 V PtCl4^{2-} + 2e- → Pt + 4Cl- E = 0.73 V account for the fact that platinum will dissolve in a mixture of hydrochloric acid and nitric acid (aqua regia) but will not dissolve in either acid alone. Problem 7. The decomposition of ozone by light can be described by the mechanism O3+light —k1→ O2 + O O+O2+M —k2→ O3 + M O+O3 —k3→ 2O2 with the overall reaction being 2O3+light → 3O2 The rate constant k1 depends on the light intensity and the type of light source used. By making a steady-state approximation for the concentration of oxygen atoms, express the rate of formation O2 in terms of the O2, O3, and M concentrations and the elementary rate constants. Show that only the ratio k3/k2, and not the individual values of k2 and k3, affects the rate. Problem 8. Hemoglobin molecules in blood bind oxygen and carry it to cells, where it takes part in metabolism. The binging of oxygen hemoglobin(aq) + O2(aq) → hemoglobinO2(aq) is first order in hemoglobin and first order in dissolved oxygen, with a rate constant of 4e7 L mol^{-1} s^{-1}. Calculate the initial rate at which oxygen will be bound to hemoglobin if the concentration of hemoglobin is 2e-9 M and that of oxygen is 5e-5 M. Problem 9. The enzyme lysozyme kills certain bacteria by attacking a suger called N-acetylglucosamine(NAG) in their cell walls. At an enzyme concentration of 2e-6 M, the maximum rate for substrate (NAG) reaction, found at high substrate concentration, is 1e-6 mol L^{-1} s^{-1}. The rate is reduced by a factor of 2 when the substrate concentration is reduced to 6e-6 M. Determine the MichaelisMenten constants Km and k2 for lysozyme. Problem 10. Consider the following nuclear decay 64 64 0 Cu → Zn + β t = 12.8 h -1 1/2 Starting with one mole of 64Cu, calculate the number of grams of 64Zn formed after 25.6 hours. Problem 11. The rate-determining step of the bromination of acetone involves breaking a carbonhydrogen bond. Estimate the ratio of the rate constants kC-H/kC-D for the reaction at 300K. The wave-numbers of vibration for the particular bonds are ν'C-H ～3000 cm^{-1} and ν'C-D ～2100 cm^{-1}. (The wavenumber ν' is given by ν/c, where ν is the frequency and c is the velocity of light.) Problem 12. Consider the following parallel first-order reactions: A —k1→ B A —k2→ C (a.) Write the expression for d[B]/dt at time t, given that [A]0 is the concentration of A at t=0. (b.) What is the ratio of [B]/[C] upon completion of the reactions. --

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