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Oxidation-reduction reactions

Oxidation-reduction reactions. Chemical Transformations. Major types of chemical reactions: Transfer of electrons between molecules in redox reactions 40% of biological reactions Transfer of protons between molecules in acid/base reactions 40% of biological reactions

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Oxidation-reduction reactions

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  1. Oxidation-reduction reactions

  2. Chemical Transformations Major types of chemical reactions: • Transfer of electrons between molecules in redox reactions 40% of biological reactions • Transfer of protons between molecules in acid/base reactions 40% of biological reactions • Transfer of atoms between molecules in breaking/making chemical bonds (condensation/hydrolysis) 20% of biological reactions

  3. Oxidation-Reduction - (redox) Oxidation Reduction • The loss of electrons from an atom or ion • The gaining of electrons by an atom or ion Lose Electrons, Oxidize Gain Electrons, Reduce LEO the lion says GER

  4. Oxidation numbers • Keep track of the positive or negative character of ions or atoms Trends: Group 1 → +1 Group 2 → +2 Group 13 →+3 Group 15 → -3 Group 16 →-2 Group 17 →-1 Metals often have different oxidation numbers depending on conditions

  5. More rules for assigning oxidation numbers: • The oxidation # of a free element = 0 • The oxidation # of a monatomic ion = charge on the ion • The oxidation # of hydrogen = +1 and rarely -1 • The oxidation # of oxygen = -2 and in peroxides -1 5.The sum of the oxidation #’s in a polyatomic ion = charge on the ion 6. Elements in group 1, 2, and aluminum are always as indicated on the periodic table

  6. The oxidation number of elements not covered by the rules must be calculated using the known oxidation numbers in a compound

  7. Practice Problems • Sb in Sb2O5 • N in Al(NO3)3 • P in Mg3(PO4)2 • O = (5)(-2) = -10 Sb = (2)(?) = +10

  8. Reducing Agents and Oxidizing Agents Reducing Agents Oxidizing Agents • The reactant that gives up electrons • The reducing agent contains the element that is oxidized (loses electrons) • The reactant that gains electrons • The oxidizing agent contains the element that is reduced (gains electron)

  9. Lets put it all together +3 -2 +2 -2 0 +4 -2 EX. Fe2O3 + 3CO → 2Fe + 3CO2 • Assign oxidation numbers • Identify which atom/ion has gained electrons and which has lost, in this case iron has been reduced/gained electrons (from +3 to 0) and carbon has been oxidized/ lost electrons (from +2 to +4) Note: iron is the oxidizing agent and carbon is the reducing agent

  10. A few more examples Assign oxidation numbers and show what is oxidized/reduced and what is the oxidizing agent/reducing agent • 2Mg + O2→ 2MgO • Al + O2 → Al2O3

  11. THE END

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