1. Electrochemistry #1

2. Redox Review
A reaction in which electrons are transferred from one atom to another is called an oxidation–reduction reaction.

3. Example
Determine what is oxidized, reduced, the oxidizing agent, & reducing agent
HCl + HNO3  HOCl + NO + H2O

4. Half Reaction Half reaction – one of the two parts of a redox reaction
One half will be oxidation
One half will be reduction

5. Step to Balancing Half Reaction Method
Separate the reactions into 2 half reactions (one for oxidation & one for reduction)
Balance each ½ reaction un the following order:
Balance elements other than H & O
Balance O by adding H2O
Balance H by adding H+
Balance the charge to make each side equal

6. Step to Balancing Half Reaction Method
Multiply each ½ reaction by a number to make the number of electrons gained = the number of electrons lost
Add the ½ reactions
Simplify
Check your work
Tip – Break things into ions or binary compounds & keep weak acids & bases together!

7. Example Fe + CuSO4  Cu + Fe2(SO4)3 ( ) 3
Fe  2Fe +3
2Fe  2Fe +3
0  +6
0  (+6e-)
2Fe  2Fe +3 +6e-
Cu +2  Cu
+2  0
e-  0
Cu e-  Cu
3Cu e-  3Cu
( ) 3
2Fe + 3Cu e-  2Fe +3 +6e- + 3Cu x x
2Fe + 3Cu +2  2Fe Cu

8. Another Example AsO4 -3 + Zn  H3As + Zn +2 +11 -3 0 0 +8 0 (+8 e-)
AsO4 -3  H3As
AsO4 -3  H3As + 4H2O
11 H+ +AsO4 -3  H3As + 4H2O
(+8 e-)
11 H+ +AsO e-  H3As + 4H2O
Zn  Zn +2
(+2 e-)
Zn  Zn e-
4Zn  4Zn e-
( )4
11H+ +AsO e- + 4Zn H3As + 4H2O + 4Zn e-
11H+ +AsO Zn H3As + 4H2O + 4Zn +2

9. Try This one… MnO4 -1 + C2O4 -2  Mn +2 + CO2
2MnO H++ 5C2O4-2  2Mn+2 +8H2O + 10CO2

10. Last one… KMnO4 + HCl  KCl + MnCl2 + H2O + Cl2
6 H+ + 2MnO HCl  2Mn +2 +8H2O + 5Cl2

11. Balancing Basic
Balancing in basic solution is just like acidic with one additional step
When balancing in acidic you will have H+ at the end
In basic you don’t want H+, you want OH-

12. To change to basic
To change to basic, simply add an equivalent number of OH- to each side and simplify

13. Example
Balancing the following by using the ½ reaction method in a basic solution
AsO4-3 + Zn  H3As + Zn +2
Acidic:
11H+ + AsO Zn  H3As + 4 H2O + 4Zn+2
Basic:
+11 OH OH-
11 H2O + AsO Zn  H3As + 4 H2O + 4Zn+2+ 11OH-
7 H2O + AsO Zn  H3As + 4Zn+2+ 11OH-

14. Another Example Ag + NO3-  Ag + + N+2 Acidic:
3Ag +6 H+ + NO3-  3Ag + + N+2+ 3H2O
Basic:
+ 6OH OH-
3Ag +6H2O + NO3-  3Ag + + N+2+ 3H2O + 6OH-
3Ag +3H2O + NO3-  3Ag + + N+2 + 6OH-

15. One More Mn(NO3)2 + NaBiO3 + HNO3  NaMnO4 + Bi(NO3)3 + H2O + NaNO3
Acidic:
2Mn H+ + 5 BiO3-  2MnO4- + 5Bi H2O
Basic:
+ 14 OH OH-
2Mn H2O + 5 BiO3-  2MnO4- + 5Bi H2O+ 14 OH-
2Mn+2 + 7H2O + 5 BiO3-  2MnO4- + 5Bi OH-

16. MEMORIZE!

17. Redox Reaction Types Watchout for:
Keywords "acidified solution" or an acid included in the reactants.
Anytime you see a neutral element, Cu°, O2, H2, etc. it must be redox.
When you recognize great oxidizers like Cr2O72-, MnO4-, and MnO2

18. Reaction Example 1
Solid copper reacts with dilute nitric acid solution

19. Reaction Example 2
A solution of potassium permanganate is mixed with an alkaline solution of sodium sulfite

20. Reaction Example 3
Hydrogen peroxide is added to a solution of iron (II) sulfate