Na 0 and Cl2 0 in 2 Na s Cl2 g ALWAYS 1Monatomic ions have an oxidation state

Na 0 and cl2 0 in 2 na s cl2 g always 1monatomic ions

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Na = 0 and Cl 2 = 0 in 2 Na( s ) + Cl 2 ( g ) ALWAYS! 1. Monatomic ions have an oxidation state equal to their charge. Na = +1 and Cl = –1 in NaCl 1. (a) Sum of oxidation states of all atoms in a “no- net charge” compound is 0. ALWAYS! Na = +1 and Cl = –1 in NaCl, (+1) + (–1) = 0
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30 Rules for Assigning Oxidation States 3. (b) The sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ion. N = +5 and O = −2 in NO 3 , (+5) + 3(−2) = −1 4. (a) Group I metals have an oxidation state of +1 in all their compounds. Na = +1 in NaCl (b) Group II metals have an oxidation state of +2 in all their compounds. Mg = +2 in MgCl 2
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31 Rules for Assigning Oxidation States 5. In their compounds, nonmetals have oxidation states according to the table below. Nonmetals higher on the table take priority. Nonmetal Oxidation State Example F −1 CF 4 H +1 CH 4 O −2 CO 2 Group 7A −1 CCl 4 Group 6A −2 CS 2 Group 5A −3 NH 3
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32 Determine the oxidation states of all the atoms in a propanoate ion, C 3 H 5 O 2 . Sum of oxidation states must be charge on the chemical species. Not a compound, is an ion. (C 3 ) + (H 5 ) + (O 2 ) = −1 Some elements have the same oxidation state in most of their compounds: H = +1 O = −2 The one unknown oxidation state is found using an algebraic expression: (C 3 ) + 5(+1) + 2(−2) = −1 (C 3 ) = −2 C = − Note: Unlike charges, oxidation states can be fractions!
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33 Examples: Assign an oxidation state to each element in the following. Br 2 K + LiF CO 2 SO 4 2− Na 2 O 2
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34 Oxidation and Reduction Another Definition Oxidation : an atom’s oxidation state increases during a reaction. Reduction: an atom’s oxidation state decreases during a reaction. CH 4 + 2 O 2 CO 2 + 2 H 2 O –4 +1 0 +4 –2 +1 –2 oxidation reduction
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35 Oxidation–Reduction Oxidation and reduction must occur simultaneously. If an atom loses electrons another atom must take them. The reactant that reduces another element is the reducing agent . The reducing agent is or contains the element that is oxidized. The reactant that oxidizes another element is the oxidizing agent . The oxidizing agent is or contains the element that is reduced. 2 Na( s ) + Cl 2 ( g ) → 2 Na + Cl ( s ) Na is oxidized, Cl is reduced Na is the reducing agent, Cl 2 is the oxidizing agent
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36 (i) Assign oxidation states (ii) determine elements oxidized and reduced (iii) determine oxidizing agent and reducing agent in the following reaction. Fe + MnO 4 + 4 H + → Fe 3+ + MnO 2 + 2 H 2 O 0 −2 +7 +1 +3 −2 +4 +1 −2 Oxidation Reduction Oxidizing Agent Reducing Agent
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37 (i) Assign oxidation states, (ii) determine the elements oxidized and reduced, and (iii) determine the oxidizing agent and reducing agent in the following reaction.
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