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Chapter 15 Oxidation and Reduction

Chapter 15 Oxidation and Reduction. 15.5 Oxidation−Reduction Reactions that Require Electrical Energy Learning Goal Describe the half-cell reactions and the overall reactions that occur in electrolysis. Nonspontaneous Oxidation−Reduction Reactions.

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Chapter 15 Oxidation and Reduction

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  1. Chapter 15 Oxidation and Reduction 15.5 Oxidation−Reduction Reactionsthat Require Electrical Energy Learning Goal Describe the half-cellreactions and the overall reactionsthat occur in electrolysis.

  2. Nonspontaneous Oxidation−Reduction Reactions • In the activity series, the oxidation of copper is below zinc. This means the reaction is not spontaneous: Cu(s) + Zn2+(aq)  Cu2+(aq) + Zn(s) Not spontaneous • To make this reaction take place, we need an electrolytic cell that uses an electrical current to drive the nonspontaneous reaction.

  3. Nonspontaneous Oxidation−Reduction Reactions Figure 15.5 In this electrolytic cell, the Cu anode is in a Cu2+ solution, and the Zn cathode is in a Zn2+ solution. Electrons provided by a battery reduce Zn2+ to Zn and drive the oxidation of Cu to Cu2+ at the Cu anode.

  4. Electrolysis of Sodium Chloride When molten NaCl is electrolyzed, • the products are sodium metal and chlorine gas • electrodes are placed in a mixture of Na+ and Cl− and connected to a battery • the products are separated to prevent them from reacting with each other

  5. Electrolysis of Sodium Chloride When molten NaCl is electrolyzed, • electrodes leave the anode as Cl− is oxidizedto Cl2 2Cl−(l)  Cl2(g) + 2 e− • electrons flow to the cathode, Na+ is reduced to sodium metal, Na 2Na+(l) + 2 e− 2Na(l) • the overall reaction is 2Cl−(l) + 2Na+(l)  Cl2(g) + 2Na(l)

  6. Electroplating Electroplating uses electrolysis to coat an object with a thin layer of metal such as silver, platinum, or gold, for example • car bumpers and hubcaps are electroplated with chromium • bowls, silverware, and platters are electroplated with silver

  7. Electroplating Eating utensils are electroplated with silver.

  8. Learning Check What half-reaction takes place when Au3+ solution is used to gold plate a stainless steel earring?

  9. Solution What half-reaction takes place when Au3+ solution is used to gold plate a stainless steel earring? The half-reaction is reduction, Au3+(aq)  Au(s) + 3 e−

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