1. What do you call a rusty cow? A Redox!

2. Balancing Redox Equations In Acidic & Basic Solution

3. When a redox equation takes place in aqueous solution, H + ions (acidic) or OH - ions (basic) are involved

4. Cr 2 O 7 2- + Fe 2+  Cr 3+ + Fe 3+ (in acidic solution = H+ ions present) Step 1: Assign oxidation numbers Cr 2 O 7 2- + Fe 2+  Cr 3+ + Fe 3+ Step 2: Determine the # of electrons transferred per atom/ion from reactants to products

5. Cr 2 O 7 2- + Fe 2+  Cr 3+ + Fe 3+ Step 3: Determine the # of electrons transferred per mole by multiplying the electrons per atom/ion by the corresponding subscript

6. Step 4: Make # electrons lost = # gained. Multiplier becomes the coefficient for that substance Cr 2 O 7 2- + Fe 2+  Cr 3+ + Fe 3+

7. Step 5: Balance the rest of the equation Cr 2 O 7 2- + Fe 2+  Cr 3+ + Fe 3+

8. Look!! We have Oxygen on one side of the equation but not the other. Add H+ to the reactant side and water to the product side in acid solution Add OH- to the product side and water to the reactant side in basic solution Cr 2 O 7 2- + 6Fe 2+  2Cr 3+ + 6Fe 3+

9. Calculate the net charge on the products and reactants Cr 2 O 7 2- + 6Fe 2+  2Cr 3+ + 6Fe 3+

10. Balance the charges by adding the number of H+ ions required. (because it’s in acid!) Balance the hydrogen & oxygen by adding water to the product side. Cr 2 O 7 2- + 6Fe 2+  2Cr 3+ + 6Fe 3+

11. CrO 2- + S 2 O 8 2-  CrO 4 2- + SO 4 2- (in basic solution) Step 1: Assign oxidation #’s

12. CrO 2- + S 2 O 8 2-  CrO 4 2- + SO 4 2- Step 2: Determine electrons transferred per atom

13. CrO 2- + S 2 O 8 2-  CrO 4 2- + SO 4 2- Step 3: Determine electrons per mole transferred

14. CrO 2- + S 2 O 8 2-  CrO 4 2- + SO 4 2- Make electrons lost = electrons gained

15. CrO 2- + S 2 O 8 2-  CrO 4 2- + SO 4 2- Balance Remaining equation

16. CrO 2- + S 2 O 8 2-  CrO 4 2- + SO 4 2- Balance by adding OH - to the product side and H 2 O to the reactant side