Final Answers - 2008 - UC BERKELEY, CHEM C130/MCB 100A,...

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UC BERKELEY, CHEM C130/MCB 100A, FALL 2008, FINAL EXAM YOUR NAME_____________________________ Page 1 of 22 UNIVERSITY OF CALIFORNIA, BERKELEY CHEM C130/MCB C100A FINAL EXAMINATION DEC. 16, 2008 INSTRUCTORS: John Kuriyan & Bryan Krantz THE TIME LIMIT FOR EXAMINATION: 2 HOURS 50 MINUTES SIGNATURE: PLEASE SIGN your name on the line above in INDELIBLE INK . XXX YOUR NAME: PLEASE PRINT your name IN INDELIBLE INK on the line above and on the top of each page. PLEASE CIRCLE your GSI’s name: Jonas Lee Mark Walker Katie Thoren Kate Engel PLEASE WRITE all of your answers AS LEGIBLY AS POSSIBLE . SCORING. For the Final Exam, eight questions are each worth 50 pts. for a total of 400 pts. QUESTION PART A PART B PART C PART D YOUR SCORE MAXIMUM POSSIBLE 1 (15) (15) (20) --- 50 2 (15) (20) (15) --- 50 3 (15) (15) (20) --- 50 4 (14) (12) (12) (12) 50 5 (8) (16) (14) (12) 50 6 (25) (25) --- --- 50 7 (24) (26) --- --- 50 8 (14) (12) (24) --- 50 GRAND TOTAL 400
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UC BERKELEY, CHEM C130/MCB 100A, FALL 2008, FINAL EXAM YOUR NAME_____________________________ Page 2 of 22 QUESTION 1 (50 pts.) (Q1.A) 15 pts. Consider the reduction of oxygen, O 2 ( g ) + 4H + + 4 e 2H 2 O . When listed in a “Chemical” table, Eº = +1.229 V ; however, when listed in a “Biological” table, Eº’ = +0.816 V . (Q1.A.i) 3 pts. Why do the two standard reduction potentials differ? For O 2 ( g ) + 4H + + 4 e 2 H 2 O, the difference between the Biological Table and the Chemical Table is the pH used as the standard condition, i.e., pH 7 and pH 0, respectively. The H + ion is part of the chemical reaction; and therefore, different standard pH conditions will lead to different standard reduction potentials (Q1.A.ii) 12 pts. Account for the exact difference in the two standard reduction potentials with a calculation. Show your work. The tables report E CHEM = +1.229 V versus E BIOL = +0.816 V. ΔE = E BIOL – E CHEM = -0.413 V For the 7 pH unit difference ΔE = RT/zF ln ((10 -7 ) 4 /(10 0 ) 4 ) where z = 4 (number of e - ) = -8.31 J mol -1 K -1 ×298 K×4×7×2.3/4/96485 C mol -1 = -0.4137 V [Note: the number of protons and electrons in the reaction cancel one another.] (Q1.B) 15 pts. An engineer wants to compare two different batteries. Each battery uses the following pairs of half reactions. The standard reduction potentials in Volts are given for each of the half reactions except one. (Design A) Ca 2+ + 2 e Ca Eº = ‒2.868 || 2H + + 2 e H 2 ( g ) Eº = ??? (Design B) Co 3+ + e Co 2+ Eº = +1.920 || Li + + e Li Eº = ‒3.050 (Q1.B.i) 3 pts. What is for the 2H + + 2 e H 2 ( g ) reaction? Explain your answer. For the 2H + + 2 e H 2 ( g ) reaction, Eº = 0 V, since it is the standard hydrogen electrode (SHE); it is the reference electrode, which is set to 0 V by definition. (Q1.B.ii) 12 pts.
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This note was uploaded on 01/27/2011 for the course MCB 100A taught by Professor Kuryian during the Spring '09 term at University of California, Berkeley.

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Final Answers - 2008 - UC BERKELEY, CHEM C130/MCB 100A,...

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