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Oxidation-Reduction

Oxidation-Reduction. Redox Reactions. In many chemical rxns electrons are transferred from one atom to another. Oxidation. Loss of electrons Creates (+) ions Increase in oxidation state 2Na + Cl 2 → 2NaCl Na is oxidized It goes from Na to Na +. Reduction. Gain of electrons

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Oxidation-Reduction

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  1. Oxidation-Reduction Redox Reactions

  2. In many chemical rxns electrons are transferred from one atom to another

  3. Oxidation • Loss of electrons • Creates (+) ions • Increase in oxidation state • 2Na + Cl2→ 2NaCl • Na is oxidized • It goes from Na to Na+

  4. Reduction • Gain of electrons • Creates (-) ions • decrease in oxidation state • 2Na + Cl2→ 2NaCl • Cl is reduced • It goes from Cl to Cl-

  5. Oxidation-Reduction reactions • Redox • A rxn in which an oxidation and reduction happen • electrons are moved from one atom to another

  6. Assigning Oxidation Numbers • Write the formula • Assign known oxidation numbers • Any free (uncombined) element = 0 • monatomic ion = charge of ion • F = -1 • more electronegative atom/PA ion = charge as an ion • G1= +1, G2= +2, Al = +3 • H +1 unless w/ a metal= -1 • O= -2 unless: w/ F =+2 ; in peroxides = -1 • Calculate the rest of the oxidation numbers • sum of O#s for molecules = 0 • sum of O#s for ions = charge on ion.

  7. Examples • CH4 C= H= • FeSO4 to find the O# for transition metal, consider charge of PA ion Fe= S= O= • NO3- N= O= • Cl2 Cl=

  8. Balancing Redox Reactions The Half-Reaction Method

  9. Remember • OIL RIG • Oxidation • Is • Loss • Reduction • Is • Gain

  10. Half-reactions • Half-reactions show where the electrons are involved • Can be • Oxidation • Reduction • 2 half-reactions make a whole reaction • All oxidation must be combined with a reduction

  11. Oxidation • Write the half rxn for the oxidation of: • Cs • Sr • Cr to Cr+3

  12. Reduction • Write the half rxn for the reduction of: • Br • O • P

  13. Redox rxns • A chemical rxn is a process in which elements undergo changes in oxidation # • At least one element is oxidized and at least one is reduced. • Na + Cl2→ NaCl • CuCl2 + Mg(OH)2 → MgCl2 + Cu(OH)2

  14. Balancing • Write the net ionic equation • Break apart the 2 half-reactions and balance each with electrons • Multiply each half-reaction by a coefficient to make the number of e- in each equal (but should be on opposite sides of the equations) • Add the 2 equations back together • Get rid of spectators

  15. SnO + Ca → CaO + Sn

  16. MnCl2 + K → Mn + KCl

  17. CuSO4 + Al → Al2(SO4)3 + Cu

  18. Agents

  19. Oxidizing and Reducing Agents • Oxidizing agent = reduced element (gains e-) • Reducing agent = oxidized element (loses e-) • 2Na + Cl2 → 2NaCl • 4Al + 3O2 → 2Al2O3 • 4Fe + 3O2 → 2Fe2O3

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