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Oxidation / Reduction By Mr. Steve Abdow. Oxidation is an increase in oxidation number Reduction is a decrease in oxidation number. 0 0 +1 -1 H 2 + Cl 2 → 2 H Cl
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Oxidation is an increase in oxidation number Reduction is a decrease in oxidation number 0 0 +1 -1 H2 + Cl2→ 2 H Cl Notice: H2 went from 0 to +1 ( oxidized ) Cl2 went from 0 to -1 (reduced)
Balancing Redox Equations by the Ion-Electron Method Divide oxidation and reduction into their individual half reactions Balance the half reactions separately Eg. balance the rxn of iron (lll) chloride, FeCl3 with tin (ll) chloride, SnCl2 Begin with a skeleton equation that shows only the ions (and sometime the molecules) used in the equation Reactants are Fe3+ and Sn2+, Products are Fe2+ and Sn4+ Skeletal Equation = Fe3+ + Sn2+ → Fe2+ + Sn4+ Divide into 2 complete half reactions a) Sn2+ → Sn4+ b) Fe3+→ Fe2 6. Balance atoms and charges on each side a) Sn2+ → Sn4+ + 2e- b) Fe3+ + e- → Fe2 7. The number of electrons gained must equal the number of electrons lost so: 2 (Fe3+ + e- → Fe2 ) needs to be used to equal the 2e- on the Sn 8. The complete equation now is: Sn2+ +2 Fe3+ +2e- → Sn4+ +2 Fe2++ 2e- 9. Drop the e- and you will get the final balanced equation for atoms and charge Sn2+ +2 Fe3+ → Sn4+ + 2 Fe2+
Balancing redox equations for Acidic Solutions Divide the skeletal equation into half reactions Balance atoms other than H and O Balance Oxygen by adding H2O to the side that needs O Balance Hydrogen by adding H+ to the side that need H Balance the charge by adding electrons Make the number of electrons gained equal to the number lost and then add the two half reactions 7. Cancel ANYHTING that is the same on both sides
Balancing redox equations for Basic Solutions Divide the skeletal equation into half reactions Balance atoms other than H and O Balance Oxygen by adding H2O to the side that needs O Balance Hydrogen by adding H+ to the side that need H Balance the charge by adding electrons Make the number of electrons gained equal to the number lost and then add the two half reactions 7. Cancel ANYHTING that is the same on both sides 8. Add to BOTH sides of the equation the same number of OH- as there are H+ 9. Combine H+ and OH- to make H2O 10. Cancel any H2O that you can