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Oxidation Reduction Reactions

Oxidation Reduction Reactions. Re-dox Reactions. Oxidation is the loss of electrons Reduction is a gain of electrons Leo goes Grr! Lose Electrons Oxidation Gain electrons Reduce. “Redox Reactions”. Many reactions involve (or seem to involve) a transfer of electrons.

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Oxidation Reduction Reactions

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  1. Oxidation Reduction Reactions

  2. Re-dox Reactions • Oxidation is the loss of electrons • Reduction is a gain of electrons • Leo goes Grr! • Lose Electrons Oxidation • Gain electrons Reduce

  3. “Redox Reactions” Many reactions involve (or seem to involve) a transfer of electrons. Such reactions always involve both: • Oxidation  Loss of electrons Na  Na+ + e- • Reduction Gain of electrons Cl + e- Cl-

  4. Determine a Redox Reaction • To determine if what you have is a redox reaction, first rewrite the equation to include the oxidation number for each element • The oxidation number is the charge an element has or appears to have when combining to form compounds

  5. Oxidizing/Reducing Agents • The element that was oxidized is part of the reducing agent. • The element that was reduced is part of the oxidizing agent.

  6. Assigning Oxidation Numbers • All pure elements and homogeneous molecules = 0 • Elements in group IA = +1 • Elements in group IIA = +2 • Ag+, Zn+2, Al+3 (unless it is a pure metal) • In binary compounds the second element = anion charge • Oxygen is almost always = -2 *unless it is O2(g) • Hydrogen is almost always = +1 *unless it is H2(g) • The total charge of a compound is always = 0

  7. A Sample Problem What are the oxidation numbers of the elements in Na2SO4? Na = +1 (times 2 atoms) = +2 O = -2 (times 4 atoms) = -8 +2 + -8 = -6 If the compound must = 0, then S must = +6

  8. Give the oxidation number for: • S in Na2SO3 • Mn in KMnO4 • N in Ca(NO3)2 • C in Na2CO3 • N in NO2- • S in SO4-2 • S in H2S2O7 • Fe in Fe(C2H3O2)2 +4 +7 +5 +4 +3 +6 +6 +2

  9. Ammonia plus Oxygen NH3 + O2 NO + H2O • Is this equation balanced? • No, it does not matter • Step 1: Rewrite the equation with the charges N3-H+3 + O02 N2+O2- + H+2O2-

  10. Ammonia plus Oxygen • Step 2: Determine the changes in the charges of each element N3-H+3 + O02 N2+O2- + H+2O2- • Nitrogen changes from 3- to 2+ • it lost an electron and was oxidized • Oxygen changes from 0 to 2- • it gains electrons and so is reduced

  11. Last Step • Step 3: If there is a species oxidized and one reduced, then it is a redox equation

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