501RedOx - Electrochemistry Chapters 5 and 20 (Petrucci et...

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Lesson 21 1 Lesson 21 Electrochemistry Chapters 5 and 20 (Petrucci et al.) Lesson 21 Oxidation states (Petrucci, section 3-4) • The oxidation state (or number) is related to the number of electrons that an atom gains, loses, or otherwise uses when combining with other atoms in a compound • The concept of oxidation state is an arbitrary one: it does not necessarily have a fundamental meaning but it is a useful concept when understanding oxidation-reduction reactions Lesson 21 Examples of oxidation states NaCl: Na has oxidation state +1 Cl has oxidation state –1
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Lesson 21 2 Lesson 21 NaCl: Na loses 1 electron → Na + Cl gains 1 electron → Cl MgBr 2 : Mg loses 2 electrons → Mg 2+ Each Br gains 1 electron → 2 Br Lesson 21 Rules for assigning oxidation states The O.S. of an individual atom in a free element is 0 – Cl, Cl 2 , N 2 , O 2 , O, etc. The total of the O.S. of all atoms in a neutral species is 0 – H 2 O (H: +1, O: –2) The total of the O.S. of all atoms in an ion equals the charge of the ion – Fe 3+ (Fe: +3), MnO 4 (Mn: +7, O: –2) Group 1 metals (Li, Na, K, Rb, Cs, Fr) have O.S. = + 1 Group 2 metals (Be, Mg, Ca, Sr, Ba, Ra) have
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This note was uploaded on 11/29/2011 for the course CHE 102 taught by Professor Simon during the Fall '08 term at Waterloo.

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501RedOx - Electrochemistry Chapters 5 and 20 (Petrucci et...

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