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practice_exam_Practice Midterm 2 Key

practice_exam_Practice Midterm 2 Key - Student Chem 152A...

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Unformatted text preview: Student #: Chem 152A Midterm 2 1 . Please clear the memory of your calculator. You may only use the notes on the one sheet of paper you have brought as discussed. This is a 50 minute exam, and is worth a total of 100 pts. 1 Please show all work. 1 A subset of the examinations will be xeroxed to guard against academic fraud. By taking this examination, you acknowledge that your exam may be xeroxed and used as evidence of fraud should this become an issue. MPWN” Potentially Useful Information: (Standard Potentials and Periodic Table are attached at the back of the exam): 1 R = 8.314 J/mol.K or 0.0821 1.atm/mol.K Na = 6.022 x 1023 molec./mol Boltzmann’s Constant: k = 1.38 x 10'23 J/K Faraday’s Constant = 96,485 C/mol h (Planck’s constant) = 6.63 x 10'34 J s c (Speed oflight) = 3 x 108 m s" mass ofelectron: 9.1 x 10'31 kg Question 1 (15 pts): Question 2 (15 pts): Question 3 (15 pts): Question 4 (15 pts): Question 5 (14 pts): Question 6 (14 pts): Question 7112 Hts}: Total (100 pts): (l) (15 pts) Consider the galvanic cell shown below (the contents of each half-cell are written beneath each compartment): 0.50 M Br2 0.20 M Cr3+ 0.10 M Br‘ The standard reduction potentials are as follows: Cr3+ + 3e" —> Cr(s) ° = —0.73 V Br2(aq) + 2e— —> ZBr- ° = +1.09 V (a) (4pts) What is E° for this cell? ,0 ,9 , , ~073V : (321/ E:»=bmw’bxw' {(o‘iv ( ) (b) (8 pts) What is the value of E for this cell at 25°C? [032 as am * Z 1: 23/367 Er; +2; 3 *3 W 2 Cralbt (C ErTé 2 Crfs) 1' 36% Q 4M ,, 9.472 Caz] 17”“ ”W (C) (3 pts) Which of the following statements about this cell is false? a This is a galvanic cell. Electrons flow from the Pt electrode to the Cr electrode. c) Reduction occurs at the Pt electrode. (1) The cell is not at standard conditions. e) To complete the circuit, cations migrate into the left half—cell and anions migrate into the right half-cell from the salt bridge. fl, -. (Hams L. E (2) (15 pts) A fuel cell designed to react grain alcohol with oxygen has the following net reaction: C2H5OH(1) + 302(g) —> 2C02(g) + 31-1200) The maximum work one mole of alcohol (CZHSOH) can yield by this process is 1320 k]. What is the theoretical maximum voltage this cell can achieve? Don’t worry about the sign: just state the magnitude of the cell potential. "mat (ma ‘L Q; H6O“( M ”'9 2%0 2&9 5Q£5W3H2Ci' (Q3 .S (05 €23 HE°CC\<\=\-w\ LCM/ta?) C/(hQC 12 ‘mo\ e ' 3 Egg“ '2 V320 \cg _ I Ecceu “ COOHA— V‘s/(JKWOG 3/6) '2 \.\Ar V i. \Z 61' "\VQ(\$‘§€T‘(CC\ {2. e“ wa\'\s-¥errc<\ (3) (15 pts) Using the following data E0 Pbo2 + 4H+ + 8042- + 2e“ —> PbSO4(s) + 2H20 +1.69 c-aHMnde 131002 + 4H+ + 2e- ~> sz+ + ZHZO +1.46 anode calculate the Ksp value at 25°C for PbSO4(s). ’ P230; ’r 496* + $04-23 29: "—a Pbooxa, (S) Jr 9320 3 P151" ~\— Zl—kzo «=7 PbO; ~¥ «W? A: 7.9.” : Pt:2+ + $04? -——3 thwarts) 0&8“ = ng v ~ \. +Ko\/ s <1.ng ”V‘FEcceu = ’RTMCVQ .— (2 mm e“ 3 (cm .48?) 9mm} (02337;) = _ (8.2M smitatzqexa MK} new = Mix/Q a , \ g 9 _ T \/\" '[pgfligc4l‘l : (95025 Mo - 2+ - '2: Pbfieatsl us; P6“ + 30+” Ks? = Wt: 3Y50+ X \ N ~ "8 0 KS?“ (fluffy/«0.1 A Eff—LEA“ "TA ‘3 (Eulov'iex Y. (4) (15 pts) Copper is electroplated from CuSO4 solution. A constant current of 4.00 amp is applied by an external power supply. How long will it take to deposit 1.00 x 102 g of Cu? The atomic mass of copper is 63.546. State your answer in hours. [Hintz the half reaction for plating Cu is: Cu2+ + 2e' -) Cu (5)] 1675 gist “73‘” “ Ze’ ; 3c/‘1m'6' J Li Awfb & 4%? (5) (14 pts) The wavelength of light associated with the n = 2 to n = 1 electron transition in the hydrogen spectrum is 1.216 x 10—7 m. By what coefficient should this wavelength be multiplied to obtain the wavelength associated with the same electron transition in the Li2+ ion? (Show work or your reasoning) i" 713’" Cot/HS DW 5 L __> is Q ‘0 (6) (14 pts) An electron in a 10.0-nm one-dimensional box is excited from the ground state into a higher energy state by absorbing a photon with wavelength 1.374 x 10’5 m. Determine the final energy level for this transition. (Show Work) ”2 nan?) t b}; 73MB ‘F ‘ ‘7\ WWKNL "I a {MS a “a a . 8CM LL A. vi mg; 5 w (7) (12 pts) How many unpaired electrons does cobalt have in its ground state? (Show work or your reasoning) PW [cg] [M 45130“ Bot mb‘rW “Pdmo‘kfima 3oz “rt 1R w nonmetal: S m e m m .u si Tran Periodic Table of the Elements *Lanthan 'Act' 232: =3=< ...
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