Tang 01 redox introduction 2

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Tang 01 redox introduction 2

  1. 1. REDOX INTRODUCTION
  2. 2. Oxidation-Reduction Reactions <ul><li>Also known as ‘redox’ reactions. </li></ul><ul><li>These reactions always occur as a pair where electrons are transferred from one atom to another. </li></ul><ul><li>LEO the lion says GER </li></ul><ul><li>OILRIG </li></ul>REDOX INTRODUCTION
  3. 3. Example #1 <ul><li>Identify the atoms being oxidized or reduced. </li></ul><ul><li>Ag + (aq) + e -  Ag (s) </li></ul><ul><li>Cu (s)  Cu 2+ (aq) + 2 e - </li></ul><ul><li>2 Na + Cl 2  2 NaCl </li></ul>Reduction Oxidation Oxidation of Na REDOX INTRODUCTION Reduction of Cl 2
  4. 4. Redox Reactions <ul><li>These reactions may also be interpreted as one reactant causing a change in the other reactant. </li></ul><ul><li>oxidizing agent – the reactant which caused the other to be oxidized (this reactant is reduced) </li></ul><ul><li>reducing agent – the reactant which caused the other to be reduced (this reactant is oxidized) </li></ul>REDOX INTRODUCTION
  5. 5. Example #2 <ul><li>For the following reactions: </li></ul><ul><ul><li>Which element is oxidized? reduced? </li></ul></ul><ul><ul><li>Identify the oxidizing agent. Reducing agent. </li></ul></ul><ul><ul><li>2 Ca + O 2  2 CaO </li></ul></ul><ul><ul><li>Mg + Br 2  MgBr 2 </li></ul></ul>Oxidized Reduced Ca: Reducing agent O 2 : Oxidizing agent Oxidized Reduced Mg: Reducing agent Br 2 : Oxidizing agent REDOX INTRODUCTION
  6. 6. OXIDATION NUMBERS
  7. 7. <ul><li>Oxidation numbers are used to keep track of electrons during reactions. </li></ul><ul><li>It is an arbitrary system based on: </li></ul><ul><ul><li>ions charge of an atom </li></ul></ul><ul><ul><li>electronegativity </li></ul></ul><ul><ul><li>For any neutral compound , the oxidation numbers of the atoms must add up to zero. </li></ul></ul>OXIDATION NUMBERS
  8. 8. Oxidation Numbers (p658) OXIDATION NUMBERS Atom or Ion Oxidation Number Examples compounds containing a single type of atom 0 Na Cl 2 H in most compounds +1 HCl H in a hydride -1 LiH O in most compounds -2 H 2 O O in a peroxide -1 H 2 O 2 monatomic ions charge of ion Na + = +1 S 2- = -2
  9. 9. Oxidation Numbers <ul><li>General steps to assign oxidation numbers: </li></ul><ul><li>Assign common oxidation numbers. </li></ul><ul><ul><li>use your periodic table!! </li></ul></ul><ul><li>The total oxidation number of a molecule or an ion is the value of the charge of the molecule or ion. </li></ul><ul><li>Unknown oxidation numbers can be assigned algebraically. </li></ul>OXIDATION NUMBERS
  10. 10. Example #3 <ul><li>Determine the oxidation numbers for: </li></ul><ul><li>MoS 2 </li></ul><ul><li>H 2 O </li></ul><ul><li>ClO 2 - </li></ul>+6 -3 +1 -2 -2 +3 OXIDATION NUMBERS
  11. 11. Example #3 <ul><li>SO 3 2- </li></ul><ul><li>Na 3 N </li></ul><ul><li>H 2 O 2 </li></ul>+4 -2 +1 -3 +1 -1 OXIDATION NUMBERS
  12. 12. <ul><li>In a redox reaction, the oxidation numbers of atoms are expected to change. </li></ul><ul><li>Oxidation is an increase in oxidation number. </li></ul><ul><li>Reduction is a decrease in oxidation number. </li></ul>OXIDATION NUMBERS
  13. 13. Example #4 <ul><li>For the following reaction: </li></ul><ul><li>identify the substance oxidized / reduced </li></ul><ul><li>oxidizing / reducing agents </li></ul><ul><li>2 KCl + MnO 2 + 2 H 2 SO 4  K 2 SO 4 + MnSO 4 + Cl 2 + H 2 O </li></ul>+1 -1 -2 +4 -2 +1 +6 -2 +1 +6 -2 +2 +6 0 +1 -2 oxidation reduction i. Cl atoms in KCl are oxidized (-1 to 0). Mn atoms in MnO 2 are reduced (+4 to +2) ii. KCl is a reducing agent. MnO 2 is the oxidizing agent. OXIDATION NUMBERS
  14. 14. HALF REACTIONS
  15. 15. <ul><li>All redox reactions may be divided into half-reactions. One half represents the oxidation, while the other is the reduction. </li></ul><ul><li>Half-reactions are always written for a single mole of a substance. </li></ul>HALF REACTIONS Zn (s) + Cu 2+ (aq)  Zn 2+ (aq) + Cu (s) Oxidation: Zn (s)  Zn 2+ (aq) + 2e - Reduction: Cu 2+ (aq) + 2e -  Cu (s)
  16. 16. <ul><li>Using the half-reactions table, one can predict whether a redox reaction will occur spontaneously. </li></ul><ul><li>An oxidizing agent (left column) will always spontaneously react with a reducing agent (right column) lower on the list. </li></ul>HALF REACTIONS
  17. 17. Yes This table is similar. The higher the voltage, the more reactive the oxidizer.
  18. 18. Example #5 <ul><li>Will iodine be able to oxidize zinc metal to Zn 2+ ions? </li></ul><ul><li>Name an oxidizing agent that can oxidize Br - to Br 2 , but cannot oxidize Cl - to Cl 2 . </li></ul>HALF REACTIONS Yes MnO 2

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