5-redox-reactions

5-redox-reactions - CHM151LL: CLASSIFICATION OF CHEMICAL...

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Classification of Chemical Reactions II–Redox Reactions OBJECTIVES: assign oxidation numbers complete and balance redox reaction equations analyze redox reaction equations o identify oxidized and reduced chemical species o identify oxidizing and reducing agents o use the activity series to predict the outcome of a proposed single-replacement DISCUSSION: Redox reactions involve changes in oxidation number or ionic charge. We use these terms to describe redox reactions. oxidation : the loss of electrons in a chemical process. In an oxidation half-reaction, the oxidation number of an atom changes in a positive direction. For example: –3 –1 or +1 +5. reduction : the gain of electrons in a chemical process. The oxidation number of an atom changes in a negative direction (e.g. –1 –3 or +5 +1). oxidizing agent : the chemical species (atom or ion) that oxidizes another and becomes reduced itself. reducing agent : the chemical species (atom or ion) that reduces another and becomes oxidized itself. Your instructor will review the rules for assigning oxidation numbers and will show you how to apply them. A brief summary of these rules follows; for a complete explanation see your textbook and/or your instructor. SUMMARY RULES FOR ASSIGNING OXIDATION NUMBERS 1. For any free element , assign an oxidation number of zero . 2. For silver or any Group 1(IA) metal in a compound, assign an oxidation number of +1 . Hydrogen in a compound is usually +1 , as well (however, in hydrides, assign –1 to H). 3. For cadmium , zinc , or any Group 2(IIA) metal in a compound, assign an oxidation number of +2 . 4. For aluminum in a compound, assign an oxidation number of +3 . 5. For any monatomic ion , assign an oxidation number equal to the ionic charge . 6. After assigning all atoms possible by rules 1-5, assign the remaining atoms: a. Select the more-electronegative atom, and assign to it an oxidation number equal to the charge it would have in a binary ionic compound. b. Assign an oxidation number to the less-electronegative atom so that the sum of all oxidation numbers is: i. equal to zero (in a compound), or ii. equal to the ionic charge (in an ion). The following examples illustrate the assignment of oxidation numbers.
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This note was uploaded on 02/28/2012 for the course CHEM 151 taught by Professor Wiley during the Spring '12 term at Mesa CC.

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5-redox-reactions - CHM151LL: CLASSIFICATION OF CHEMICAL...

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