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Mid2-white - First Letter of last name Chem 1B Midterm...

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Unformatted text preview: First Letter of last name Chem 1B Midterm 2 (exam B), Winter 2006 This exam should contain 7 pages (this cover sheet, 4 pages of exam, one sheet of information and a periodic table). Please count to make sure your exam is complete with no blank pages. You have 50 minutes to complete the exam. Show all work and box your final answer to receive maximum possible credit. The exam is out of a total of 100 points. Good luck! Exam 2 p. 1 Chem. 18 2006 l) (35 points total) a) (8 pts.) What is the oxidation state (number) for: i) O in 02 __.Q_ ____ __ ii) Bi in NaBiO3 ___i§______ iii) P in Mgzrzoj ___i_§‘_____c iv) Br in HOBr _n_:l'_L..._____ b) (9 pts.) Balance the following oxidation—reduction reaction, which occurs in acidic solution: MnO4'(aq) + Fe2+(aq)-> Fe3+(aq) + Mn2+(aq). 3 __ ._. (liar? It; lP-l-c )Xb C) (8 pts.) True/ False. Circle the correct response. i) In a galvanic cell, oxidation occurs at the anode. F ii) In an electrolytic cell, electrons flow from anode to cathode. T F iii)Aluminum is quite resistant to corrosion because it is thermodynamically impossible for Al to be oxidized by 02. T F iv)A good oxidizing agent is difficult to reduce. T F d) (10 pts.) Fill in the blanks. / i) For second order kinetics, you expect a plot of __H__£__J_ ____ __ vs. time to yield a straight line. ii) A salt brid __ e is necessary for the functioning of a galvanic cell because it allows __ _Q;¢i___n to flow from one compartment to the other, thus preserving charge neutrality while allowing current to flow. iii)Hydrated FeZO3 is an everyday consequence of electrochemistry. Its common name is [V5 f" iv)The below diagrams show different ways to wire two identical batteries and a motor together. Each battery produces a potential of 1.5 V. The voltage expected at the motor for arrangement (1) is _’~ 5‘V The voltage expected at the motor for arrangement (2) is fifilf Exam 2 p. 2 Chem. 1B 2006 2) (10 pts.) The equilibrium constant, K, for the dissociation reaction of C12 Clag) “ 2c1(g) (.— was measured as a function of temperature (in OK). A graph of ln(K) VS. 1/ T for this reaction gives a straight line with a slope of —1.352x104°K and a y—intercept of 14.51. What are the values of AH" and A50 for this reaction? 47AM) : Ac." am“— 72350 W: —%’5(%) W3; w W 5 4,; c {494479 7’" _5¢p“( Alto: :: 1,35‘a'lx/oq'k A$’-3/‘f% 7A?) 1350 : “""NLXQ: ""3'/*8°>~% "1 @N“ 3) (10 pts.) Calculate the cell potential, E, for a concentration cell based on Cu(s)/Cu2+(aq) redox chemistry. [Cuzt] = 1.0x10'3 M in one of the compartments and [Cub] = 2-0 M in the other compartment. Both compartments use Cu electrodes and the cell is at 25°C. Cu +C/‘HZQ/4) —->2(o +CJDMCOOI/4J 1433 E 0:20 (-5qu ’04,” {‘4 59/1! (OMflcr/Vl‘9HM/5) _________—r f 5 2‘" «image» :0 — Lg”; Ag (£351: :2 [:01V Exam 2 p. 3 Chem. 1B 2006 4) (10 pts.) Lead (Pb) is electroplated out of solution from its aqueous ion in the +2 oxidation state. Assuming a current of 2 amperes was used for a duration of 10 minutes, how many grams of solid lead are plated out of solution? 54»- ’C/s RAM/(9e? 4P5 gin/P16.1 _..———- W meme awn,— ,W/a P4 31% X 605 X/OVHHJC' /Mw/ e—F x X :1sz 5) (20 pts.) The rate law for a reaction is found to be Rate = 1([A]2[B]. Of the following three mechanisms, which ones are consistent with this rate law? MW. Mechanism A WE Mechanism g; E k A + B —>4‘_ E (fast) A + B “H E (fast) A + A g E (slow) k k‘l [ (-I k ( E+B"—°>C+D(slow) E+A£>C+D(slow) E+B—>‘C+C(fast) “44: k3 r916 2 Fqu: k( 3' KMNBJHQEEJ Wzfiffl’lifli ({laun PNt/Jou)) “0+ (C'T SI'34¢1¢_ / -—-\'——-‘.> : lg 1 J at Kiri/Ms] 1 (“9,544+ PM; [015;fiéflL [1; El Exam 2 p. 4 Chem. 1B 2006 6) (15 pts.) The following initial rate data were collected for the reaction 2Mn04' + 5H2C204+ 6H 9 ZMn2+ + 10C02+ 8H20 Exp. # [MnO4‘]0(M) [H2C204]0(M) [H+]0(M) Initial Rate (M/s) 1 1x10‘3 X; 1 x 10-3 1.0 2 x 10-4 x 2 2x103) Mao-3%; 1.0 X 8x104 (2 7 3 2 x 10-3 2 x 10-39 1.0%) $1.6 x 10-3 4 2 x 10-5 2 x103 20'} 1.6 x 1062"] Determine the rate law for this reaction and calculate the rate constant. ma: kmadMgochMI/fli (2p -——~7 [4:2 (fa/.4 Off/ow: (4 EW4 ) {up 19) -——)M:/ ...
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Mid2-white - First Letter of last name Chem 1B Midterm...

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