Fall 01. Exam2 key

Fall 01. Exam2 key - Chem 2101 Hour Exam IV NAME 2001 Chem...

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Chem 2101 Hour Exam IV 2001 NAME
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Chem 2101 Hour Exam IV 2001 If you do NOT want me to return your exam in the big pile -> check this box A -> and give us your e-mail address: Your Name: This Exam Will be filled out by graders. Score: 1. /45 Previous Exams My score hour exam I 2. /15 My score hour exam II 3. /20 My score hour exam III 4. /20 To the students: Please check your scores after you get the exam back and contact Phil Buhlmann if any of these scores is incorrect. Total: /100 Please note that we do this as a service to you. We try to do our best to detect any errors as early as possible. Instructions: * Use equations and tables provided on exam as needed * Show all work for which you expect credit * Put your name on every page * Write in ink to be eligible for a regrade
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Chemistry 2101 Introductory Analytical Chemistry Fall 2001 This sheet of equations will be provided on the fourth Hour Exam. Note that you are still responsible for knowing what the equations mean, and how to apply them. Ox + n e - == Red, E = E o - 0.059 V n log [Red] [Ox] {at 25 o C}; E = E o - R T n F ln [Red] [Ox] E = E o + R T F n x ln { a X + k x,y a Y n x /n y } E = E o + 0.059 V n x log { a X + k x,y a Y n x /n y } {at 25 o C} Use standard reduction potentials from the attached table wherever needed.
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Name 1 An electrochemical measurement involving a sample of Cr 2 O 7 2- and Cr 3+ . (a) (5 points) A solution in contact with a platinum working electrode is 10 -3 M in Cr 2 O 7 2- and 10 -2 M in Cr 3+ . Formulate the reduction-oxidation reaction involving the two chromium species at the platinum electrode. Cr 2 O 7 2- + 14 H + + 6 e - == 2 Cr 3+ + 7 H 2 O (b) (10 points) If the pH is 2.0 and the temperature 25 o C, what is the potential of the half cell described in (a)? E = E o - 0.059 V n log [Red] [Ox] = E = 1.36 V - 0.059 V 6 log [Cr 3+ ] 2 [Cr 2 O 7 2- ] [H + ] 14 = E = 1.36 V - 0.059 V 6 log (10 -2 ) 2 (10 -3 ) (10 -2 ) 14 = 1.09 V
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Name (c) (5 points) The above mentioned half cell with the two chromium species is now combined with a silver/silver chloride reference electrode to give an electrochemical cell. Draw a schematic of the resulting electrochemical cell. Assume that the solution in contact with the electrode is saturated with KCl. The bridge electrolyte is 3.5 M KCl. (d) (10 points)
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This note was uploaded on 10/02/2011 for the course CHEM 2101 taught by Professor Bulman during the Spring '11 term at Minnesota.

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Fall 01. Exam2 key - Chem 2101 Hour Exam IV NAME 2001 Chem...

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