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Expt9_redox - Experiment 9 Oxidation Reduction Electron...

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121 Experiment 9 Oxidation / Reduction Electron Transfer Reactions Expt 9 Redox.wpd INTENT In this experiment you will focus on the atomic model interpretation of the most easily recognized chemical reactions of common experience, namely the oxidation/reduction reactions. Key Terms and Concepts (familiarize yourself with them): C conjugate oxidizing agent & reducing agent relationship C oxidation & reduction (oxidation states) C oxidizing agent & reducing agent C metal & nonmetal activity series DISCUSSION Most people have no trouble recognizing the combustion of fuels, the rusting of iron, or the digestion of foods by an organism as examples of chemical reactions. These reactions are all examples of redox reactions. Reduction-oxidation (redox) reactions create new compounds by exchanging electrons and thereby fundamentally changing the reacting particles. These kinds of reactions will be examined in this experiment. Before we look at any specific reactions, let us define some of the basic terms of redox reactions. Originally the term oxidation described what happens to any substance that reacted with oxygen, O 2 , and in so doing lost electrons. The term has now been generalized so that: Oxidation is any process which increases the oxidation state of an atom due to the loss of electrons. Reduction is any process which reduces the oxidation state of an atom due to the gain of electrons. The actual species involved in these reactions are the oxidizing agents and the reducing agents. By taking on electrons the oxidizing agent causes something else to be oxidized (lose electrons). C The oxidizing agent is the electron acceptor and it is reduced . By giving up electrons, the reducing agent causes something else to be reduced (gain electrons). C The reducing agent is the electron donor and it is oxidized . These processes may seem very confusing at first. To avoid confusion we treat redox reactions as those in which electrons are transferred from the reducing agent to the oxidizing agent.
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122 In order to understand the stoichiometry of redox reactions we will focus on the number of electrons gained by the oxidizing agent and lost by the reducing agent. We will need to identify how many moles of electrons are given up by each mole of reducing agent and how many moles of electrons are accepted by each mole of oxidizing agent. Since mass and energy are neither created nor destroyed in a chemical reaction, the number of electrons given up by the reducing agent must be the same as the number accepted by the oxidizing agent. That is, they must exchange an equal number of electrons. Thus their coefficients in the chemical equation must represent equivalent quantities of electrons. For example, consider the reaction of Zn and Cu 2+ ion in solution: oxidation: Zn (s) ! Zn 2+ (aq) + 2e & reduction: Cu 2+ (aq) + 2e & ! Cu (s) net reaction: Zn (s) + Cu 2+ (aq) ! Cu (s) + Zn 2+ (aq) In the example above the electrons lost in the oxidation equation equal the electrons gained in the reduction equation. Sometimes, in order for the number of electrons accepted to be equal to the number
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