Unformatted text preview: CHEM 1311 Dr. Charlie Cox Summer 2009 Guidelines: Exam #2, 100 points 16 July 2009 Name_______________________________ Closed NOTE/Closed BOOK 1. Write your name at the top of every page. 2. Turn off cell phones and other electronic devices other than a calculator. 3. Do not begin until instructed to do so. 4. No communication is permitted. 5. All materials must be put away. 6. One hour and 45 minutes is allotted for the exam. You may take a break as needed. 7. Please submit the exams when time is called. Instructions for submission will be provided. 8. SHOW all work for partial credit. 9. Regrade requests must be submitted one week after the exam is permitted. 10. GOOD LUCK! Useful Formulas and Constants: me = 9.11 x 10‐31 kg ao = 52.9 pm Zeff = Z‐S h = 6.626 x 10‐34 Js c = speed of light = 3.0 x 108 m/s RH = 2.18 x 10‐18 J 1 C = 1 J/1V !Go = ‐nFEo F = 96485 C/mole R = 8.314 J/mol K E = Eo – (RT/nF) ln Q 1. Explain the following trends in terms of acid strength or base strength. (21 points, 3 pts each) a. HClO4 is a stronger acid than HBrO4. ______________________________________________________________________ ______________________________________________________________________ b. HClO3 is a stronger acid than HClO2. ______________________________________________________________________ ______________________________________________________________________ c. H2O is a stronger acid than NH3. ______________________________________________________________________ ______________________________________________________________________ d. Methyl amine is a stronger base than pyridine (C5H5N) ______________________________________________________________________ ______________________________________________________________________ e. Cr6+ is a stronger acid than Cr3+ ______________________________________________________________________ ______________________________________________________________________ f. NO2‐ is a stronger base than NO3‐ ______________________________________________________________________ ______________________________________________________________________ g. The acid‐base equilibrium constant for Co3+ and 3,5‐diethylpyridine is greater than the equilibrium constant for Co3+ and 2,6‐diethylpyridine. The structures for the pyridine compounds are shown below. ______________________________________________________________________ ______________________________________________________________________ N N 2. Given the reaction: Pb | Pb2+ || Al3+ | Al answer the following questions. (14 points) a. Write the reaction that is occurring at the anode _____________________________ (1) b. Write the reaction that is occurring at the cathode___________________________ (1) c. What is oxidized? ______________________ (1) d. What is reduced? ______________________ (1) e. What is the overall equation? _____________________________________________ (1) f. What is the electrochemical potential at standard state? ______________________ (1) g. If PbCl2 (0.8 M) and AlCl3 (0.5 M) were initially present, what potential would be initially observed? ______________________________ (2) h. What is the Gibb’s Free energy for this process? ___________________________ (1.5) i. j. What is the value of the equilibrium constant at equilibrium? ________________ (1.5) k. What is the value of the potential at equilibrium?__________________________ (1.5) What is the value of the equilibrium constant for this process? _______________ (1.5) 3. Given the following reaction: SO32‐ (aq) + MnO4‐ (aq) ! SO42‐ (aq) + Mn2+ (aq) (8 points) a. What is the oxidation state of sulfur “S” in SO32‐? ___________________________ (1) b. What is the oxidation state of manganese “Mn” in MnO4‐? ____________________ (1) c. Draw an electrochemical cell depicting the following (4) i. The cathode ii. The anode iii. The flow of electrons iv. The movement of ions through the salt bridge v. All electrodes needed for the electrochemical cell d. What is the electrochemical potential at standard state? _____________________ (2) 4. Given the following Pourbaix diagram, answer the proceeding questions. (7 points) a b c d e f g h pH a. Using the letter designations, indicate the regions that are undergoing acid‐base equilibrium. (multiple letters are possible) ________________________________ (2) b. Using the letter designations, indicate the regions that are pH independent (multiple letters are possible) ________________________________ (2) c. Using the letter designations, indicate the regions that are pH dependent (multiple letters are possible) ________________________________ (2) d. What species has the greatest oxidation state of Cr? _________________________ (1) 5. Complete the following steps in balancing an oxidation‐reduction reaction. (3 points) a. Balance the oxidation atoms: CrO4‐ ! Cr3+ __________________________________________________________________ (1) b. Balance the hydrogen atoms: MnO4‐ ! MnO2 + 2H2O ___________________________________________________________________ (1) c. Balance in basic media: MnO2 ! Mn2+ + 2H2O ___________________________________________________________________ (1) 6. Given the Latimer diagram below, answer the following questions (6 points): a. How is the diagram arranged? ________________________________________ ___________________________________________________________________ (1) b. Write the reaction for the disproportionation of NO2: _____________________________________________________________________ (2) c. What is the potential associated with the disproportionation of NO2? ___________ (2) d. What is the potential for the process: NO ! HNO2? __________________________ (1) 7. Name or draw each of the following coordination compounds. (16 points, 2 points each) a. K2[V(SO4)2(CN)3(OH2)] ___________________________________________________ b. Mer‐tribromotricarbonylcolbalt (III) c. Fac‐tribromotricarbonylcolbalt (III) d. trans‐dibromodichloroplantinum (IV) e. [Ni(NH)3(py)]SO4 ______________________________________________________ Py = pyridine f. [Mn(en)3](NO3)2 _______________________________________________________ g. "#[Mn(en)3] 8. Identify the following as stereoisomers or constitutional isomers. Then identify the more specific type of isomerism: (a.) linkage (b.) enantiomers (c.) geometric (d.) ionization. (8 points, 2 points/each) (i.) Stereoisomer or constitutional O O Mn O O O O vs. O Mn O O O
O O O specific type ______________________ O acac CO Co CO CO (ii.) Stereoisomer or constitutional CO Cl Co OC CO Cl Cl vs. Cl Cl Cl specific type ______________________ specific type ______________________ (iii.) Stereoisomer or constitutional [Ni(CO)3Br]Cl vs. [Ni(CO)3Cl]Br (iv.) Stereoisomer or constitutional Cis‐[PtBr2Cl2] vs. specific type ______________________ trans‐[PtBr2Cl2] 9. Explain whether or not the following is chiral (i.e. has a non superimposable mirror image) (5 points) Br O Mn O Br
O O O O acac 10. Draw the d‐energy levels for the following complexes indicating whether they are low spin or high spin. (12 points, 3 points/each) a. Tetrahedral [NiCl4]SO4 b. Octahedral c. Octahedral [MoCl6] d. Octahedral [Fe(py)6]Br3 [Co(OH2)6]Br3 ...
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