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Oxidation-reduction reactions

Pgs 636 - 645. Oxidation-reduction reactions. Oxidation-Reduction Reactions. Reactions that occur when electrons are transferred between atoms Also called Redox Reactions Oxidation = LOSS of electrons Reduction = GAIN of electrons LEO the lion goes GER. Oxidation – Reduction Reactions.

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Oxidation-reduction reactions

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  1. Pgs 636 - 645 Oxidation-reduction reactions

  2. Oxidation-Reduction Reactions • Reactions that occur when electrons are transferred between atoms • Also called Redox Reactions • Oxidation = LOSS of electrons • Reduction = GAIN of electrons • LEO the lion goes GER

  3. Oxidation – Reduction Reactions • Reaction of sodium metal with chlorine gas: 2Na (s) + Cl2(g) 2NaCl (s) • What’s really happening in this reaction? Na Cl Na Cl Na+Cl- Na+Cl- Each sodium gives-up an electron to the chlorine resulting in ions!

  4. Practice!! • In each of the following reactions, identify what is being oxidized, and what is being reduced? 2Mg (s) + O2(g) 2MgO (s) 2Al (s) + 3I2(s) 2AlI3(s)

  5. Can reactions between nonmetals be redox reactions? • Yes, but it’s harder to see CH4(g) + 2O2(g) CO2(g) + H2O (g) + energy • Use oxidation statesto determine where the electrons are going!

  6. Oxidation States • Also called oxidation numbers • Positive and negative numbers assigned to an INDIVIDUAL atom to help of keep track of electrons during redox reactions

  7. Rules for Assigning Oxidation Numbers • Oxidation number of a free element = zero Examples  HONClBrIF, solid metals (Na, Ag) • Oxidation number of a monatomic ion is the same as it’s charge Examples  NaCl CaCl2 • Oxygen’s oxidation number in compounds is -2, EXCEPT for peroxides where it is -1 Examples  O2 H2O H2O2

  8. Rules for Assigning Oxidation Numbers • Hydrogen’s oxidation number = +1 in covalent compounds Examples  H2O HI NH3 • For a neutral compound, the sum of the oxidation states must be ZERO Examples  CuCl2 Fe2O3 • For polyatomic ions, the sum of the oxidation numbers must equal the charge of the ion Examples  SO42-

  9. Practice!! • Assign oxidation numbers to each of the following atoms: SO3 N2O5 C2H6 SO32-PF3

  10. What do we use oxidation numbers for? • To determine what is being oxidized and what is being reduced in a redox reaction • Example: • Identify what is oxidized and reduced in the following reaction: HINT  Oxidation = INCREASE in oxidation # Reduction = DECREASE in oxidation # CH4(g) + 2O2(g) CO2(g) + H2O (g)

  11. Practice!! • Determine what is oxidized and reduced in the following reactions: Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 + 2Ag Br2 (g) + 2NaF (aq)  2NaBr (aq) + F2 (g) CH3OH (g) + O2 (g)  CO2 (g) + H2O (g)

  12. Two more terms to know… • Reducing Agent electron donor • What is oxidized in the reaction • Oxidizing Agent electron acceptor • What is reduced in the reaction • Identify the reducing agent and oxidizing agent in the previous 3 reactions: Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 + 2Ag Br2 (g) + 2NaF (aq)  2NaBr (aq) + F2 (g) CH3OH (g) + O2 (g)  CO2 (g) + H2O (g)

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