1. Electrochemistry Lesson 4 Balancing Half Reactions

2. Review Questions

3. Non spontaneous- uphill Does Cl 2 react with F - ?

4. Spontaneous downhill Does S 2 O 8 2- react with Pb?

5. spontaneous- downhill Can you keep HCl in a Fe or a Ag container? HCl → H + + Cl - 2H + + 2e - → H 2(g) Fe(s) → Fe 2+ + 2e - 2H + + Fe → H 2(g) + Fe 2+ Yes No

6. Can you keep HNO 3 in a Au or a Ag container? NO 3 - + 4H + + 3e - → NO (g) + 2H 2 O Ag → Ag + + e - NO 3 - + 4H + + 3Ag → NO (g) + 2H 2 O + 3Ag + Yes No x 3

7. Core Concepts What is reduced and oxidized? What gains or loses electrons? What are the oxidizing and reducing agents? +3 +5 +5 +3 2H + + As 2 O 3 + 2NO 3 - + 2H 2 O  2H 3 AsO 4 + N 2 O 3 oxidizedreduced loses e'sgains e's red agentox agent

8. Core Concepts Is the following a redox reaction? 1 6 -2 1 -2 1 1 6 -2 1 -2 H 2 SO 4 + 2KOH  K 2 SO 4 + 2H 2 O Not Redox- no change in Oxidation number

9. PbCl 2 reacts with Mn but not Br -. O.A R.A Pb 2+ Mn Br - Br 2 Mn 2+ Pb Br 2 Pb 2+ Mn 2+ Rank the oxidizing agents in decreasing strength (from strongest to weakest) Rank the reducing agents in decreasing strength. MnPbBr -

10. Balancing Redox Half Reactions in Acid Solution Cr 2 O 7 2- →Cr 3+ 1. Balance the central atom 2.Balance O by adding H 2 O 3.Balance H by adding H + 4.Balance the charge by adding electrons 5.Check charge 2+ 7H 2 O+ 14H + +12 +6 6e - + most positive side

11. Balancing Redox Half Reactions in Acid Solution HV 2 O 5 3- →H 2 VO 3 + 1. Balance the central atom 2.Balance O by adding H 2 O 3.Balance H by adding H + 4.Balance the charge by adding electrons 5.Check charge 2H 2 O ++ H + -2+2 + 4e - -2

12. Balancing Redox Half Reactions in Acid Solution HBr 2 O 7 2- → H 2 BrO 2 - 2+ 3H 2 O+ 9H + 9e - + +7-2

13. Balancing Redox Half Reactions in Acid Solution 9e - + HBr 2 O 7 2- + 9H + → 2H 2 BrO 2 - + 3H 2 O To balance in base solution………. 1.Balance in acid 2.Add OH - to each side to neutralize H + 3.Simplify 9H2O9H2O 9OH - 6

14. Balancing Redox Half Reactions in Acid Solution 9e - + HBr 2 O 7 2- + → 2H 2 BrO 2 - +-11 6H2O6H2O9OH -

15. TRY: Balance in alkaline(basic) solution. Au+ ClO - →HAuCl 4 2- 4+ 4H 2 O9H + + +5-2 7e - + -2

16. Balance in alkaline solution. + 7e - + Au+ 4 ClO - →HAuCl 4 2- + 4H 2 O 9H 2 O 9OH - 9H +

17. Balance in alkaline solution. 5H 2 O + 7e - + Au + 4ClO - →HAuCl 4 2- + 9OH - -11

18. Homework Page 203 #19(odd), 20, 22, 23