Chp19,Balancing_Redox_Eqs-1 - Chang, 6th Edition, Chapter...

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Chang, 6 th Edition, Chapter 19, Worksheet #1 S. B. Piepho, Spring 2000 How to Balance Equations for Oxidation-Reduction Reactions Oxidation-reduction (redox) reactions are reactions in which oxidation numbers change. Oxidation numbers are either real charges or formal charges which help chemists keep track of electron transfer. In practice, oxidation numbers are best viewed as a bookkeeping device. Oxidation cannot occur without reduction. In a redox reaction the substance which is oxidized contains atoms which increase in oxidation number. Oxidation is associated with electron loss (helpful mnemonic: LEO = L oss of E lectrons, O xidation ). Conversely, the substance which is reduced contains atoms which decrease in oxidation number during the reaction. Reduction is associated with electron gain (helpful mnemonic: GER = G ain of E lectrons, R eduction ). Chemists often talk about oxidizing and reducing agents. Be careful with these terms! An oxidizing agent is a substance which oxidizes something else : it itself is reduced! Also, a reducing agent is a substance that reduces another reactant : it itself is oxidized. A disproportionation reaction is a reaction in which the same element is both oxidized and reduced. How to Assign Oxidation Numbers: The Fundamental Rules Rules for assigning oxidation numbers are as follows: The oxidation number of any pure element is zero . Thus the oxidation number of H in H 2 is zero. The oxidation number of a monatomic ion is equal to its charge . Thus the oxidation number of Cl in the Cl - ion is -1, that for Mg in the Mg +2 ion is +2, and that for oxygen in O 2 - ion is -2. The sum of the oxidation numbers in a compound is zero if neutral , or equal to the charge if an ion . The oxidation number of alkali metals in compounds is +1, and that of alkaline earths in compounds is +2. The oxidation number of F is -1 in all its compounds. The oxidation number of
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This note was uploaded on 02/16/2012 for the course CHEM 130 taught by Professor Staff during the Fall '08 term at Orange Coast College.

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Chp19,Balancing_Redox_Eqs-1 - Chang, 6th Edition, Chapter...

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