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 Notice: H 2 went from 0 to +1 (

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Presentation transcript:

Oxidation is an increase in oxidation number Reduction is a decrease in oxidation number H 2 + Cl 2 → 2 H Cl Notice: H 2 went from 0 to +1 ( oxidized ) Cl 2 went from 0 to -1 (reduced)

Balancing Redox Equations by the Ion-Electron Method 1.Divide oxidation and reduction into their individual half reactions 2.Balance the half reactions separately Eg. balance the rxn of iron ( lll ) chloride, FeCl 3 with tin ( ll) chloride, SnCl 2 1.Begin with a skeleton equation that shows only the ions 2. (and sometime the molecules) used in the equation 3.Reactants are Fe 3+ and Sn 2+, Products are Fe 2+ and Sn Skeletal Equation = Fe 3+ + Sn 2+ → Fe 2+ + Sn 4+ 5.Divide into 2 complete half reactions a) Sn 2+ → Sn 4+ b) Fe 3+ → Fe 2 6. Balance atoms and charges on each side a) Sn 2+ → Sn e - b) Fe 3+ + e - → Fe 2 7. The number of electrons gained must equal the number of electrons lost so: 2 (Fe 3+ + e - → Fe 2 ) needs to be used to equal the 2e - on the Sn 8. The complete equation now is : Sn Fe e - → Sn Fe e - 9. Drop the e- and you will get the final balanced equation for atoms and charge Sn Fe 3+ → Sn Fe 2+

Balancing redox equations for Acidic Solutions 1.Divide the skeletal equation into half reactions 2.Balance atoms other than H and O 3.Balance Oxygen by adding H2O to the side that needs O 4.Balance Hydrogen by adding H+ to the side that need H 5.Balance the charge by adding electrons 6.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 1.Divide the skeletal equation into half reactions 2.Balance atoms other than H and O 3.Balance Oxygen by adding H 2 O to the side that needs O 4.Balance Hydrogen by adding H + to the side that need H 5.Balance the charge by adding electrons 6.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 H 2 O 10. Cancel any H 2 O that you can