Practice Exam 3 KEY

Practice Exam 3 KEY - Hunter College City University of New...

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Chem. 104 Exam III practice Summer 2010 1) Consider the oxidation in aqueous solution of iron to iron (III) by the reduction of Cr 2 O 7 2- to Cr 3+ . What is the balanced half reduction reaction? a. 14H + + Cr 2 O 7 2- + 6e- 2Cr 3+ + 7H 2 O b. Cr 2 O 7 2- 2Cr 3+ + 7O + 6e- c. 14H + + Cr 2 O 7 2- + 3e- Cr 3+ + 7H 2 O d. Cr 2 O 7 2- + 3e- Cr 3+ 2) What is the anode and the cathode, the direction of electron flow, and the direction of any ion flow respectively. a. Fe, Pt, left to right, in salt bridge anions flow left, cations flow right. b. Fe, Cr 3+ , left to right, in salt bridge anions flow left, cations flow right. c. Fe , Cr 2 O 7 2- , right to left, in salt bridge anions flow left, cations flow right. d. Fe (III), Cr 2 O 7 2- , right to left, in salt bridge anions flow right , cations flow left. 3) What is the standard cell potential for this cell at 298 K? a. 0.376 V b. 1.294 V c. 0.304 V d. 1.366 V 4) If the concentrations in the cell were: [Fe 3+ (aq)] = 1.3 mM, [Cr 3+ (aq)] = 3.2 mM, and [Cr 2 O 7 2- (aq)] = 1.0 M, with a pH of 2, what would the cell potential at 298 K be? a. 1.69 V b. 1.196 V c. 0.304 V d. 1.536 V 5) There is a large contract for silver plating ashtrays .You will immerse the ashtrays in a solution of silver nitrate and run a current to plate them. The contract calls for deposing 8.5g silver on each ashtray, and you can spend no longer than 30 minutes per ashtray to plate them. What is the minimum current you will need for this job? a. 7.5x10
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Practice Exam 3 KEY - Hunter College City University of New...

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