gammon win07 exam2 v.B

gammon win07 exam2 v.B - Ker v.4. Chemistry 152A, Winter...

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Unformatted text preview: Ker v.4. Chemistry 152A, Winter 2007 Hour Exam #2, version #1 FRI, March 2, 2007 REINHARDT & course staff Name ; Section : TA Name UW-ID # ; Signature ; Your signature above attests to your certification that your have neither received nor given improper help for this exam, from written, verbal, or electronic sources, and that all work shown is you own. Should you turn in this exam for a “re- grade” that no changes, what so ever, have been made to any answers or work shown. Note that we routinely Xerox exams before returning them. All students must sit in their assigned seat, unless given permission to "move" at the start of the exam by your TA. No student may leave his/her seat during the exam. This hour exam is “worth” 100 points, maximum, 50 minutes in class. Closed book, closed notes, only "simple" calculators. Other calculators, and other electronic devices will be confiscated (& returned at the end of the exam)! No programmable calculators, laptops, graphing calculators, cell-phones, Palm Pilots, BlackBerrz'es, etc. are allowed. WORK need NOT be shown for any of the multiple choice (or short answer) problems of questions #1—8, 6 points each, for a total of 48 points. Note that if you are asked for “more than one” answer you may earn “partial credit!” But, we will also subtract points fo “incorrect answers!” ‘ READ EACH of THESE CAREFULLY! Work must be clearly shown, or the appropriate questions answered, for problems 9-12, and 13, worth a total of 52 points to obtain credit. \ "N0 work = N0 credit". where work is required. Show work and answers in indicated spaces! If you need extra space for "work", you may use the back of the page on which the problem appears: BUT, you must indicate that we should look for work shown on the back of a page, by writing a note on the page where the problem appears. There are 13 problems. These are p_0_t of equal value(s) or difficulty, so use your time well. For problems 1-8, where almost no computational work is required, so if you do not see "the answer" in less than a "minute," move on, and then come back if you have time. Possibly useful information, and a periodic table appear as the last two pages of this exam. You may remove and NOT HAND IN these last pages, if you find that convenient. But be sure that no work is left behind with them! Scores: '11 _..____’ ....._____. 1____;2_____;3____;4____;5_____;6_____;7__;8___:9___:10 12 313 . Total /100 READ EACH PROBLEM CAREFULLY! l. (6 pts) Circle all correct statements! Correction will be made for i ' A voltaic cell has an 8° value of —l.00 V. e reac ion in such a cell: +3 0) is not spontaneous I has K > 1 K 1 «rs e) has a negative AG° 2. (6 pts) The reduction activity series: Reaction 8° (volts) F2 + 2e' —> 2F' +2.87 C12 + 2e" —> 2C1" +1.36 Ag + e —> Ag—y +0.80 é—Cuz + 2e —> Cu +0.34 Fe2 + 26' —> Fe —0.44 A13+ + 3e‘ —9 Al ~1.66 Na+ + e' —> Na -2.71 An excess of finely divided metallic copper (Cu) is stirred up with a solution which contains “substantial” Ag+ ions, and the system is allowed to come to equilibrium. The solid materials are then filtered off and electrodes of solid copper and solid silver are inserted into the remaining solution. Which of the following is a correct statement (circle all "correct" possibilities, points will be subtracted for incorrect answers!) m * 3 u metal will be one of the solids filtered off. - T here will be substantial Ag+ ions in the remaining in the solution. c) a cell voltage of + 0.46 volts will be measured. d) a cell voltage of ~ 0.46 volts will be measured. 0g metal will be one of the solids filtered off. 1‘3 (4 pts) Given the reduction activity series: Reaction 8° (volts) F2 + Ze' —> 2F' +2.87 C12 + 26- —> 201- +1.36 Ag+ + e' ——> Ag +0.80 Cu2+ + 26' —> Cu +0.34 Fe2+ + 26- —> Fe -0.44 A13+ + 36' —> A1 -1.66 V Na+ + e' —> Na 271 Which of the following would be the best reducing agent? a) C12 Consider the cell above at 25°C. the standard reaction potentials are as follows: *0 art. 4 of gr“ + 36' = Cr(s) Br2(aq) + 26' = 2Br‘ [Cr'3+] = 0.01M [Br'] =0.01M PBfiatm. 80 80 —0.73 V +1.09 V Which of the following statements about this cell are TRUE? Circle ALL correct answers, points will be deducted for incorrect answers! he system above is a galvanic cell. Electrons flow, through the wire, from the Pt electrode to the Cr electrode. eduction occurs at the Pt electrode The cell is not at standard conditions. To complete the circuit negative ions migrate into the left half-cell and positive ions migrate into the right half-cell, both via the salt bridge. +1 ’thY. sn (3 pts each) Write the electron configuration for the following: A) 4‘ ‘ a B)As 4‘1 Edi, (3 points each) How many "unpaired" electrons will there be in the ground state of the ground states of the ions: A) Fe3+ ? # of unpaired electrons = = l l i B) .Ca2+ ? # of unpaired electrons = L u ‘0 D (6 pts) Which of the following is a correct statement about quantum numbers for the H-atom, OR for the "aufbau" principle for building the periodic table of the elements (points will be deducted for incorrect answers!): W a) if I = 2 there are two nodes in a hydrogenic wavefunction 'f n = 3 there are two nodes in a hydrogenic wavefunction changing m1, changes the number of nodes in a hydro genie orbital 'n the aufbau, filling the n = 3 shell requires 18 electrons. ' the aufbau, a likely configuration for Fe3+ is [Ar]3d5. -/I|,2 49—i- ,1. {WW7 fi‘u kit-J (6 pts) Which of the following statements is TRUE (points will be deducted for incorrect answers)? ’2 a) The second ionization potential of Na is greater than that of Li. b) The ionic radius of A1+3 is larger than that of 1363+. c The ionization energy of F" is less than that of Cl'. he atomic radius of Fr is larger than that of Cs. The element "At" has an exceptionally negative electron affinity. FOR Problems 9-10 WORK must be shown to obtain credit. Work shown is worth 10 points, the correct result is worth an additional 2 points. 9. (12 pts) Circle correct answer, and briefly answer the question below. Which of the electron orbital occupation filling diagrams shown is the ground state configuration for the given element or ion? Circle all correct answers! Points will be subtracted for incorrect answers! a)Cu: mg; 11%11 127,1 b)Fe3+; mg. 1131(111 ELiL c)Br':[Ar]_::_ EE%EE« T.ng WORK: for each “incorrect” electron orbital filling diagram, write the correct electron configuration, by configuration is meant 1322s22p6. . ..etc., or for more electrons, [Ar] 4s2.... ! 10. (12 pts) SHOW WORK! When an electron in 3 3p orbital of a sodium atom makes a transition to the 3s orbital, a photon of wavelength 589.6 nm is emitted. The “magnitude” difference in energies between these 3p and 3s orbitals is: a) 3.37x10'18J » ~ .37 x10'19J 'L 3.37 x10+19J d) 3.37 x 10'17 J c) none ofthese to within 3 sig. figs. 7 I: ‘ um =- l‘: =' We“ "(aim 12) 28 points. ALL WORK MUST BE SHOWN! Given the two REDUCTION half cell reactions and values of the half cell "standard" reaction potentials: Half reaction - 8° 1(vo; + 2H” + e' —> VO2+ + H20 1.00 (volts) GH++ 2e' ——> H2(gas) 0.00 (volts) .— I a) Write a "balanced" equation, using the above balanced half cell reactions as a starting point, for the reaction: H2(gas) + VOz+ ——-> VO2+ + H20 in acid solution (so Hir "might" be a reactant or product). SHOW work! ' J!’ + ‘ +£- 2qu ‘l’U-I *Hy-ELbfi 44%» b) What is the “standard” cell potential for the reaction written in the “direction as written above?” Get the Sign Right! V = I 0° (volts) c) What would you expect the observed cell potential to actually be if the partial pressure of H2(gas) is 0.1 atm, and the concentration of all other ions are 0.1 M? The "activity" or effective concentration of H20 may be assumed to be "1". AND which is the “spontaneous direction of the reaction?” Forward or backwards, as written under these conditions? (0.1 atm H2 and all ions at 0.1M) Assume T = 25°C. Again show all work! Be sure that the sign is consistent with the direction of the reaction as written in part a) : SHOW ALL WORK! Put ANSWER on next page! o ackward” spontaneously circle one, and state why! Voltage under above 1 ' 1' ' The reaction goes “ . o C u + ’l'ué'fl d) Both of the half-reactions above take place at “Pt” (platinum, expensive!) electrodes which allow the transfer of electrons, but are completely inert. Neither takes part in any chemistry, and thus these electrodes do not appear in the balanced equation, nor in the expression of Nernst’s Law! In the sketch of a cell below, write in one of the half reactions at the left electrode (beaker A) , the other at the right electrode (beaker B), and THEN: Show the direction of the actual flow of electrons through the “wire”, under the conditions of part c) above. This “direction” must be consistent with the “Sign” of your result in part c), and with which half reaction you chose to “put” in which beaker. ALA» an in) (- T4 ...
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gammon win07 exam2 v.B - Ker v.4. Chemistry 152A, Winter...

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