1. Mullis1 Oxidation  When a substance loses electrons, it undergoes oxidation. Ca(s) + 2H + (aq)  Ca 2+ (aq) + H 2 (g)  Ca lost 2 electrons to the H + ions.  The metal Ca became an ion: Ca 2+  Ca has been oxidized.  H + was the oxidizing agent. (It made oxidation happen.)

2. Mullis2 Oxidation examples  Originally, oxidation referred to the combination of a substance with oxygen. 4Fe + 3O 2  2Fe 2 O 3 4Fe + 3O 2  2Fe 2 O 3Oxidation state of Fe 0  +3 2CO + O 2  2CO 2 2CO + O 2  2CO 2Oxidation state of C +2  +4

3. Mullis3Reduction  When a substance loses electrons, it undergoes oxidation. 2Ca(s) + O 2 (g)  2CaO (s)  O gained 2 electrons to become O 2- in CaO.  The neutral O 2 became an ion: O 2-  O 2 has been reduced.  In all reduction-oxidation reactions, one species is reduced at the same time as another is oxidized.

4. Mullis4 Reduction examples Originally, reduction referred to the removal of oxygen from a compound. Oxide ores are reduced to metals—a real reduction in mass. WO 3 + 3H 2  W + 3H 2 O WO 3 + 3H 2  W + 3H 2 OOxidation state of W +6  0

5. Mullis5 Recognizing a Redox Reaction  Analyze oxidation numbers.  If no elements change in oxidation numbers from reactant side to product side, the reaction is NOT redox.  If changes occur, the reaction is redox.  Another clue that the reaction is redox are the words “in acidic conditions/solution” or “in basic conditions/solution.”

6. Mullis6 LEO says GER (Identifying ½ Reactions)  Lose Electrons Oxidation / Gain Electrons Reduction  Assign oxidation numbers 1st  Ex. H 2 + Cl 2  2H Cl 0 0 +1 -1 0 0 +1 -1  Pick the element that goes down in Oxidation Number: Here, this is Cl (0  -1). Its half reaction is: Here, this is Cl (0  -1). Its half reaction is:  Cl 2 + 2e -  2Cl - Cl is reduced  Pick the element that goes up in Oxidation Number: Here, this is H (0  +1). Its half reaction is: Here, this is H (0  +1). Its half reaction is:  H 2  2H + + 2e - H is oxidized

7. Mullis7 Water  Oxidation of water: 2H 2 O  O 2 +4H + + 4e -  Reduction of water: 2H 2 O + 2e -  H 2 +2OH -

8. Mullis8 Redox Equation Example SbCl 5 + KI  KCl + I 2 + SbCl 3 SbCl 5 + KI  KCl + I 2 + SbCl 3 +5 -1 +1 -1 +1 -1 0 +3 -1 LEO: 2I -  I 2 + 2e - (ox # increased) GER: Sb 5+ + 2e -  Sb 3+ (ox # decreased) _________________________________________________ Sb 5+ + 2I -  Sb 3+ + I 2

9. Mullis9 Balancing Redox Equations 1. Write the two half-reactions. 2. Balance all elements except O and H. 3. Balance O with waters. 4. Balance H with H +. 5. Balance the charge with electrons (e -1 ). 6. Multiply by a factor to make the electrons equal for both equations. 7. Add the two equations together and combine like terms. If a basic solution, do number 8. If a basic solution, do number 8. 8. Add hydroxides (OH - ) to both sides equal to the H +. On the side with the H +, addition of OH - will produce water molecules. 8. Add hydroxides (OH - ) to both sides equal to the H +. On the side with the H +, addition of OH - will produce water molecules. (H + + OH -  H 2 O). Combine waters if necessary. (H + + OH -  H 2 O). Combine waters if necessary.  Hint: Balance all redox equations as if they are in acidic solution. If they are in a basic solution, convert it over at the end using step 8.

10. Mullis10 Redox Equation Example (acidic solution) H 3 PO 4 + HNO 2  N 2 O 4 + H 3 PO 3 H 3 PO 4 + HNO 2  N 2 O 4 + H 3 PO 3 +1 +5 -2 +1 +3 -2 +4 -2 +1 +3 -2 LEO: HNO 2  N 2 O 4 (ox # increased) 2HNO 2  N 2 O 4 + 2H + + 2e - (balance with H + and e - ) 2HNO 2  N 2 O 4 + 2H + + 2e - (balance with H + and e - ) GER: H 3 PO 4  H 3 PO 3 (ox # decreased, acid was reduced) H 3 PO 4  H 3 PO 3 + H 2 O (balance O with H 2 O ) H 3 PO 4  H 3 PO 3 + H 2 O (balance O with H 2 O ) H 3 PO 4 + 2H + + 2e -  H 3 PO 3 + H 2 O (balance with H + and e - ) _________________________________________________ H 3 PO 4 + 2HNO 2  N 2 O 4 + H 3 PO 3 + H 2 O (add ½ reactions)

11. Mullis11 Common Oxidizing Agents  Free halogen (Cl 2 ) Halide ion (Cl - )  Metal-ic (high) Fe 3+ Metal-ous (low) Fe 2+  MnO 4- (acid) Mn 2+  MnO 4- (base) MnO 2  MnO 2 (acid) Mn 2+  Cr 2 O 7 2- (acid) Cr 3+  HNO 3 (conc.) NO 2  HNO 3 (dilute) NO  H 2 SO 4 (hot) SO 2  H 2 O 2 H 2 O

12. Mullis12 Common Reducing Agents  Halide ion (Cl - ) Free halogen (Cl 2 )  Metal-ous (low) Fe 2+ Metal-ic (high) Fe 3+  Free metal (Cu) Metal ions (Cu 2+ )  Sulfite ion(SO 3 2- ) Sulfate ion(SO 4 2- )  Nitrite ion(NO 2 - ) Nitrate ion(NO 3 - )  C 2 O 4 - (oxalate ion) CO 2