Chapter20blackrw2 - 20 Electrochemistry Visualizing...

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Unformatted text preview: 20 Electrochemistry Visualizing Concepts 20.2 (a) If a Zn(s) strip was placed in a CdSO 4 (aq) solution, Cd(s) would form on the strip. Although º red E for Zn 2 + (aq), –0.763 V, and Cd 2 + (aq), –0.403 V, are both negative, the value for Cd 2 + is larger (less negative), so it will be the reduced species in the redox reaction. (b) If a Cu(s) strip was placed in a AgNO 3 (aq) solution, Ag(s) would form on the strip. Although º red E for Cu 2 + (aq), 0.337 V, and Ag + (aq), 0.799 V, are both positive, the species with the larger º red E value, Ag + , will be reduced in the reaction. 20.4 The species with the largest º red E is easiest to reduce, while the species with the smallest, most negative º red E is easiest to oxidize. (a) The species easiest to oxidize is at the bottom of Figure 20.14. (b) The species easiest to reduce is at the top of Figure 20.14. 20.6 The main difference between a fuel cell and a battery is that a fuel cell is not self-contained. That is, there is a continuous supply of fuel (reductant) and oxidant to the cell, and continuous exhaust of products. The fuel cell produces electrical current as long as reactants are supplied. It never goes ”dead.” 20.8 Unintended oxidation reactions in the body lead to unwanted health effects, just as unwanted oxidation of metals leads to corrosion. Antioxidants probably have modes of action similar to anti-corrosion agents. They can preferentially react with oxidizing agents (cathodic protection), create conditions that are unfavorable to the oxidation-reduction reaction, or physically coat or surround the molecule being oxidized to prevent the oxidant from attacking it. The first of these modes of action is likely to be safest in biological systems. Adjusting reaction conditions in our body can be dangerous, and physical protection is unlikely to provide lasting protection against oxidation. Anti-oxidants are likely to be reductants that preferentially react with oxidizing agents. 58 20 Electrochemistry Solutions to Black Exercises Oxidation States 20.10 (a) Reduction is the gain of electrons. (b) The electrons appear on the reactants side (left side) of a reduction half-reaction. (c) The reductant is the reactant that is oxidized; it provides the electrons that are gained by the substance being reduced. (d) A reducing agent is the substance that promotes reduction. It donates the electrons gained by the substance that is reduced. It is the same as the reductant....
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This note was uploaded on 05/05/2008 for the course CHEM 101 taught by Professor Farahh during the Spring '02 term at UNC.

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Chapter20blackrw2 - 20 Electrochemistry Visualizing...

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