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Oxidation and Reduction

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Oxidation and Reduction

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  1. Oxidation and Reduction

  2. Oxidation-Reduction • Oxidation-Reduction reactions are electron transfer reactions. • Also called Redox Reactions.

  3. Oxidation:the loss of electrons increases Mg0 Mg2+ + 2e- (half rxn) 2-8-2 2-8 Mg lost 2 electrons = oxidized

  4. Reduction:the gaining of electrons reduces S0 + 2e-  S2- (half rxn) 2-8-6 2-8-8 S gains 2 electrons = Reduction

  5. Redox When oxidation and reduction both take place. **Electrons go from the metal to the nonmetal. Mg + S  MgS (net equation) Mg  lost electrons  oxidation S  gains electrons  reduction

  6. You can’t have one… without the other! • Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. • You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation LEO the lion says GER! ose lectrons xidation ain lectrons eduction GER!

  7. Another way to remember • OIL RIG s s xidation ose eduction ain

  8. Review of Oxidation Numbers The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. • Free elements (uncombined state)  oxidation number = zero. Na, Fe, K, Pb, H2, O2, P4 = 0 • In compounds use periodic table and they add to zero. 2+ 2- 3+ 2- Fe O Fe2 O3 • Polyatomic ions add to the charge on the ion. +5 -2 +5 + -6 = -1 N O3 N O3 -

  9. Oxidation numbers of all the atoms in…? +4 -2 +4 -2 S O2 C O3 2- +1 +6 -2 -2 -3 +1 +1 -2 Na2 SO4 ( ) (NH4)2S

  10. Oxidation • The oxidation number increases • Metals oxidize • LEO (less electrons = oxidation) • Reduction needs to take place for there to be oxidation

  11. Reduction • The oxidation number decreases • Nonmetals reduce • GER (gain electrons = reduction) • Oxidation needs to take place for reduction

  12. Old definition: Gaining oxygen = oxidation Losing oxygen = reduction