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Chapter 19

Chapter 19. Redox Reactions. Oxidation Numbers. Rules Uncombined element = 0 Monatomic ion = charge on ion (from location of periodic table) 2 element compound – right gets what it wants (from periodic table), calculate left

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Chapter 19

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  1. Chapter 19 Redox Reactions

  2. Oxidation Numbers • Rules • Uncombined element = 0 • Monatomic ion = charge on ion (from location of periodic table) • 2 element compound – right gets what it wants (from periodic table), calculate left • 3 element compound – right and left get what they want, calculate left • Examples

  3. Oxidation-Reduction (Redox) • Oxidation • Loss of e- (becomes more positive) • Reduction • Gain of e- (becomes more negative) • LEO the lion says GER • Loss of e- is oxidation • Gain of e- is reduction • Example

  4. Recognizing Redox Reactions • THERE HAS TO BE A CHANGE IN OXIDATION NUMBER FOR A REACTION TO BE REDOX!! • Examples

  5. Half-Reactions • Separate redox reaction into the individual oxidation and reduction reactions • Examples Mg + O2 -> MgO

  6. Redox Reactions • Oxidizing Agent • Substance that causes oxidation • It is Reduced! • Reducing Agent • Substance that causes reduction • It is Oxidized!

  7. Balancing Half-Reactions • Steps: • Write half-reactions separately • Balance everything except H and O • Balance O by adding water • Balance H by adding H+ • Balance overall charge by adding e-’s • Add oxidation and reduction reactions with equal e-’s • Cancel if possible

  8. Balancing Half-Reactions • Example: H2S + O2 -> SO2 + H2O

  9. Balancing Half-Reactions Example: MnO4- + I- -> MnO2 + I2

  10. Balancing Half-Reactions Example: MnO4- + H2O2-> Mn+2 + O2

  11. Electrochemistry • Using half-reactions and calculating voltages • Anode • Site of oxidation • Cathode • Site of reduction • Use the REDUCTION POTENTIAL CHARTS and ONE will FLIP to make the MOST POSITIVE TOTAL • MULTIPLYING BY COEFFICIENT DOES NOT CHANGE VOLTAGE

  12. Calculating Voltage for a Cell

  13. Electrochemistry • Examples

  14. Calculating Voltage for a Cell • What two half reactions will occur? • What is the oxidation half reaction? • What is the reduction half reaction? • What would the voltage reading be for the entire cell? • Which electrode would get bigger? • Which electrode would be consumed?

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