14.Oxidation_reduction_Section_I

14.Oxidation_reduction_Section_I - Chapter 14: section I,...

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Chapter 14: section I, Part 1 Redox Oxidation-Reduction reactions Lectures will built on and use concepts covered in chapter 8 ---
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Historical background Oxidation of iron by oxygen Redox reactions were discovered in studies of corrosion of Fe by O 2 to form rust 4Fe + 3O 2 -> 2Fe 2 O 3 Because that reaction involved O 2 chemists coined the term oxidation However, Redox reactions might or might not involve oxygen ---------------------
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Why should we learn Redox reactions? Important in: Industry Organic chemistry Biochemistry (chemistry of living systems) In fact: Without Redox reactions, no life (as we know it) would exist on earth ---
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Underlying concept Oxidation reduction reactions involve transfer of electrons from an electron donor to an electron acceptor Oxidation and reduction are coupled ( Oxidation does not occur without reduction ) -----
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A simple example reaction between sodium and chlorine 2 Na(s) + Cl 2 (g) -> 2 NaCl (s) On the left side, the charge on Na and Cl is zero because the elements are in unreacted state Examine the reaction in the context of Lewis dot representation (page 299-300) Na has 1 valence electron Cl has 7 valence electrons In the shown reaction An electron is transferred from Na to Cl Na is the electron donor Cl the electron acceptor --
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Half-reactions Redox reactions can be separated into two parts: Reduction half-reaction Oxidation half-reaction Use of half-reactions helps to identify electron donor and electron acceptor in redox reactions --
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Redox half reactions for 2 Na(s) + Cl 2 (g) -> 2 NaCl (s) Recall: the charge of an electron is -1 Half-reactions Na -> Na + + e - Na electron donor Cl + e - -> Cl - Cl electron acceptor ______________ Net reaction Na + Cl -> Na + + Cl - (in solid form NaCl) In nature, Cl exists as Cl 2 2 Na + Cl 2 -> 2 NaCl ---
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The element that donates electrons is called a reducing agent The element that gains electrons is called an oxidizing agent 2 Na + Cl 2 -> 2 NaCl Na is the reducing agent (Na donates an electron; the charge on Na goes from 0 to +1) Cl is the oxidizing agent o (Cl accepts the electron; the charge on Cl goes from 0 to -1) -------------------------- Learn the terminologies: they are used interchangeably
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Oxidation state or oxidation number Redox reactions are described in term of a parameter known as Oxidation state (or oxidation number ) For example, for the reaction of 2 Na + Cl 2 -> 2NaCl The oxidation state of Na changes from 0 to +1 The oxidation state of Cl changes from 0 to -1 -----------
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Learn to identify Redox reactions 2 Na + Cl 2 -> 2 NaCl (redox reaction) NaCl -> Na + + Cl - (not redox, it represents ionization of NaCl in water) Other examples of ionization of chemical compounds in water: ZnCl 2 -> Zn 2+ + 2 Cl - CuCl 2 -> Cu 2+ + 2 Cl - ---
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Reaction of Zn with CuCl 2 (Fig. 14.5) If we place a zinc (Zn) strip in a solution of CuCl 2 (blue) In the course of the reaction,
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This note was uploaded on 04/03/2011 for the course CHEM 112 taught by Professor Harwood during the Spring '11 term at Purdue University-West Lafayette.

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14.Oxidation_reduction_Section_I - Chapter 14: section I,...

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