Homework 10 Solutions

Homework 10 Solutions - ENMA 300/ENME 382 HW 10 Due. Nov....

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ENMA 300/ENME 382 HW 10 Due. Nov. 28, 2011 1. Callister 16.2 (modified) (a) Compute the voltage at 25°C of an electrochemical cell consisting of pure lead immersed in a 5 × 10 –2 M solution of Pb 2+ ions, and pure tin in a 0.25 M solution of Sn 2+ ions. (a) Since tin is lower in the standard emf series (Table 16.1), we will begin by assuming that tin is oxidized and lead is reduced, as and Equation 16.20 takes the form = – 0.011 V since, from Table 16.1, the standard potentials for Pb and Sn are –0.126 and –0.136, respectively. (b) Write the spontaneous electrochemical reaction. Since the V is negative, the spontaneous cell direction is just the reverse of that above, or (c) What is one common application for Pb-Sn materials? If the Pb-Sn were used near the ocean (on a ship or near the shore), could the reaction above occur? Eutectic Pb-Sn has traditionally been used for solders. To determine if the electrochemical cell in b could occur on the surface of a soldered joint you need to determine whether it is likely that Pb or Sn could be dissolved in moisture from humidity or rainwater. Pb is insoluble in water in the absence of nitric acid or concentrated sulfuric acid. However, PbO has a solubility of 0.0023 g/100 ml of cold water. Tin (Sn) is also insoluble on water in the absence of acids. SnO 2 is also insoluble in water. Thus, I would expect 1
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solder joints to be electrochemically stable in the absence of acid contaminants. Notes – 1. I used the
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This note was uploaded on 04/03/2012 for the course ENME 382 taught by Professor Christou during the Spring '12 term at Maryland.

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Homework 10 Solutions - ENMA 300/ENME 382 HW 10 Due. Nov....

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