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Reduction-Oxidation Reactions (1)

Reduction-Oxidation Reactions (1). 213 PHC 4th lecture (1) Gary D. Christian, Analytical Chemistry,6 th edition. By the end of the lecture the student should be able to:. Balance a redox reaction. Detect the end point in redox reaction. Half-Reaction  Method. Balancing Redox Reactions.

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Reduction-Oxidation Reactions (1)

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  1. Reduction-Oxidation Reactions (1) 213 PHC 4th lecture (1) Gary D. Christian, Analytical Chemistry,6th edition.

  2. By the end of the lecture the student should be able to: • Balance a redox reaction. • Detect the end point in redox reaction.

  3. Half-Reaction Method Balancing Redox Reactions I- + MnO4- → I2 + Mn2+ • Separate the reaction into two half reactions: I- → I2 MnO4- → Mn2+

  4. Balance the atoms of each half-reaction: first balance all of the atoms except H and O. For an acidic solution add H2O to balance the O atoms and H+ to balance the H atoms. In a basic solution use OH- and H2O to balance the O and H. Balance the iodine atoms: 2 I- → I2 The Mn in the permanganate reaction is already balanced, so let's balance the oxygen: MnO4- → Mn2+ + 4 H2O Add H+ to balance the 4 waters molecules: MnO4- + 8 H+ → Mn2+ + 4 H2O The two half-reactions are now balanced for atoms.

  5. Balance the charges in each half-reaction: The reduction half-reaction should accept the same number of electrons as the oxidation half-reaction loss. This is accomplished by adding electrons to the reactions: 2 I- → I2 + 2e- 5 e- + 8 H+ + MnO4- → Mn2+ + 4 H2O

  6. Multiply the electrons by a number: The two half-reactions should have the same number of electrons so they can cancel each other: 5 (2I- → I2 +2e-) 2 (5e- + 8H+ + MnO4- → Mn2+ + 4H2O)

  7. Add the two half-reactions: 10 I- → 5 I2 + 10 e- 16 H+ + 2 MnO4- + 10 e-→ 2 Mn2+ + 8 H2O This gives the final equation: 10 I- + 10 e- + 16 H+ + 2 MnO4- → 5 I2 + 2 Mn2+ + 10 e- + 8 H2O

  8. Get the overall equation: Cancel out the electrons and H2O, H+, and OH- that may appear on both sides of the equation: 10I- + 16 H+ + 2 MnO4- → 5 I2 + 2 Mn2+ + 8 H2O

  9. Check the numbers: Make certain that the mass and charge are balanced. In this example, the atoms are balanced with a +4 net charge on each side of the reaction. 10 I- + 16 H+ + 2 MnO4- → 5 I2 + 2 Mn2+ + 8 H2O

  10. Follow the link: http://www.youtube.com/watch?v=EtOrcKw6wso&feature=endscreen&NR=1 How to balance a redox reaction in acidic solution. http://www.youtube.com/watch?v=imqYliG5BCU&feature=fvwrel How to balance a redox reaction in basic solution.

  11. Self-Indication Detection Of The End Point • Highly colored • e.g. potassium permanganate purple) MnO4- + 5e = Mn2+ (purple) (colorless)

  12. Starch Indicator • Used with iodine • Strach-I2 complex (dark blue)

  13. Redox Indicators • Highly colored dyes • Weak reducing or oxidizing agents • The color of the reduced and oxidized forms are different • The color will change with E change during titration • Eo of indicator must be near the E of eq. point • The redox indicator reaction must be rapid • E.g. Diphenylamine

  14. SUMMARY • Balancing redox reactions. • Indicators used to detect the end point in redox reaction. Thank You

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