S-11 OX-RED_review - REDOX REACTIONS REVIEW Redox reactions...

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REDOX REACTIONS REVIEW Redox reactions or oxidation-reduction reactions involve transfer of electrons. As the electron transfer occurs, substances undergo changes in oxidation number. OXIDATION AND REDUCTION Oxidation: the process by which a compound looses or appears to loose electrons. It corresponds to an increase in the oxidation number. Reduction: the process by which a compound gains or appears to gain electrons. It corresponds to a decrease in oxidation number OXIDATION NUMBERS Oxidation numbers are used to keep track of electron transfer. Oxidation numbers are assigned to ionic as well as molecular compounds. Oxidation numbers are assigned per atom. OXIDIZING AND REDUCING AGENTS Oxidizing agent: species that causes oxidation. An oxidizing agent accepts electrons from the species it oxidizes and therefore, an oxidizing agent is always reduced. Reducing agents: species that causes reduction. A reducing agent donates electrons to the species it reduces and therefore, a reducing agent is always oxidized. Example Zinc, Zn, reacts with copper (II) ions, Cu 2+ , to give Zn 2+ and copper, Cu. -----Zn------------ is being oxidized and --- Cu 2+ ------------ is being reduced. The oxidizing agent is ----- Cu 2+ -------------- and the reducing agent is --Zn-- The oxidation number of Zn is zero (free element). As it reacts and turns into the Zn ion, its oxidation number changes to +2. This is an oxidation. The oxidation number of copper changes from +2 to 0. This is a reduction. Because Zn metal was oxidized, it is the reducing agent and Copper (II) is the oxidizing agent. 1
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HOW ARE OXIDATION NUMBERS ASSIGNED? 1. The oxidation number of a free element is zero. 2. The oxidation number of an element in a monatomic ion is the charge on the ion. 3. When combined, Grp IA elements have ox. number of +1. 4. When combined, Grp IIA elements have ox. number of +2. 5. When combined, Grp IIIA elements have ox. number of +3. 6. When combined, fluorine has an ox. number of –1. 7.
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This note was uploaded on 05/12/2011 for the course CHEM 302 taught by Professor Mccord during the Spring '10 term at University of Texas at Austin.

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S-11 OX-RED_review - REDOX REACTIONS REVIEW Redox reactions...

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