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General Chemistry Principles, Patterns, and Applications, 2011

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different potato; when a wire connects the two potatoes, the clock begins to run as if it were connected to a<br />

battery.<br />

a. Draw a cell diagram of the potato clock.<br />

b. Explain why the clock runs.<br />

14. ♦ The silver–zinc battery has the highest energy density of any rechargeable battery available today. Its use is<br />

a.<br />

presently limited to military applications, primarily in portable communications, aerospace, <strong>and</strong> torpedopropulsion<br />

systems. The disadvantages of these cells are their limited life (they typically last no more than<br />

about 2 yr) <strong>and</strong> their high cost, which restricts their use to situations in which cost is only a minor factor. The<br />

generally accepted equations representing this type of battery are as follows:<br />

2AgO( s) + Zn( s) + H2O( l) ® Ag2O( s) + Zn( OH )2( aq) E° = 1.85 V<br />

Ag2O( s) + Zn( s) + H2O( l) ® 2Ag( s) + Zn( OH )2( aq) E° = 1.59 V<br />

reaction <strong>and</strong> calculate E° cell .<br />

Write the overall cell<br />

b. If the cell is 75% efficient, what is the maximum amount of work that can be generated<br />

from this type of battery?<br />

c. Use tabulated data to calculate the maximum work that can be generated by a lead<br />

storage cell. If a silver–zinc battery is operating at 100% efficiency, how do the two<br />

batteries compare?<br />

15. All metals used in boats <strong>and</strong> ships are subject to corrosion, particularly when the vessels are operated in salt<br />

water, which is a good electrolyte. Based on the data in the following table, where potentials are measured<br />

using a glass electrode, explain why<br />

a. iron or steel should not be used in bolts in a lead ballast keel.<br />

b. ordinary brass should not be used as a structural fastening, particularly below the<br />

waterline.<br />

c. an aluminum hull should not be painted with a copper-based antifouling paint.<br />

d. magnesium sacrificial anodes are preferred over zinc when a vessel is kept in fresh water.<br />

e. Monel (an alloy that contains mostly nickel <strong>and</strong> copper) is preferred over stainless steel for<br />

freshwater tanks.<br />

Metal<br />

E versus Ag/AgCl (V)<br />

titanium 0.02<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

1811

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