1. Oxidation, Reduction, and Electrochemistry

2. TOPIC 1: Half Reactions
Objective: Determine oxidation numbers for elements in a compound, identify the oxidized and reduced species, write half reaction, and balance ionic reactions

3. I. What is Electrochemistry?
The study of electricity and how it relates to chemistry
Electricity is caused by the movement of _____________
We will be focusing on how energy is produced/converted by electrochemical cells:
Voltaic -_______________________________
Electrolytic - __________________________
charges (e-)
Produces electrical energy
(ie. – battery)
Uses electrical energy to produce a chemical reaction
(ie. – electroplating)

4. I. What is Electrochemistry?
chemical reactions
Within these cells there are _____________________ that involves a ____________________
These chemical reactions are called _________________
Reduction: _________________ and the ion becomes ______________________
Oxidation: ______________________ and the ion becomes ______________________
transfer of electrons
redox reactions
gain of e-
more negatively charged
loss of e-
more positively charged

5. I. What is Electrochemistry?
Way to remember it:
“LEO says GER”
LOSS of
Electrons is
OXIDATION
GAIN of
Electrons is
REDUCTION

6. II. Assigning Oxidation Numbers
The first step in determining which species was oxidized and which was reduced is knowing what the charge of each species starts at and ends at, so you can determine whether electrons were lost or gained. Why is that important?
Ever put a battery in backwards? It doesn’t work! Circuits are designed to only let electrons through ONE way. It is possible to destroy an electronic device by putting the battery in backwards. We need to know which end is – (the end that loses electrons, oxidation) and which end is + (the end that gains electrons, reduction), so we need to know how to find the charges (oxidation numbers) of the species involved!

7. II. Assigning Oxidation Numbers
Rules for assigning oxidation number (REVIEW):
1. Each uncombined element has an oxidation number of _________
Example: 2Na + Cl2 2NaCl
__________________ has an oxidation number (charge) of _______
2. If an element has only ______ oxidation number (charge) listed on the ___________________, then that is its oxidation number when in a compound USUALLY
Examples: Na has a charge of __________
Ca has a charge of __________
Al has a charge of __________
O has a charge of __________
zero
Na and Cl2
zero
one
periodic table
+ 1
+ 2
+ 3
- 2

8. II. Assigning Oxidation Numbers
Rules for assigning oxidation number (REVIEW):
3. The sum of all charges in an compound equals _____
Examples: Show that the sum of the charges equals zero for the following compounds:
NaCl Li3N MgCl2
ZERO
1(+1) + 1(-1) = 0
3(+1) + 1(-3) = 0
1(+2) + 2(-1) = 0

9. II. Assigning Oxidation Numbers
Rules for assigning oxidation number (REVIEW):
4. The sum of all charges in a polyatomic ion equals ___________________________
Examples: Identify the charges for the following PAI:
SO4 NO3 S2O3
the net charge for the ion
- 2
- 1
- 2

10. III. Identifying the Oxidized and Reduced SPECIES
If the charge becomes more positive going from left to right, the species is __________ and _______________
If the charge becomes more negative going from left to right, the species is _________ and _________________
Spectator Ions _________________________________
OXIDIZED
LOSES ELECTRONS (OX # ↑)
REDUCED
GAINS ELECTRONS
(OX # ↓)
ION THAT DOES NOT CHANGE CHARGE

11. III. Identifying the Oxidized and Reduced SPECIES
For the following reactions, identify the species (symbol AND charge) that undergoes oxidation, reduction or is the spectator ion (if available):
 2Na + Cl2  2 NaCl
Oxidized ______ Reduced _________ Spectator Ion ______ +1 -1
Nao
Cl2o
NONE

12. III. Identifying the Oxidized and Reduced SPECIES+2 -2
2CaO  2 Ca + O2
Oxidized _______ Reduced ________ Spectator Ion _______
3 Mg + 2 Au(NO3)3  3 Mg(NO3)2 + 2 Au
Oxidized _______ Reduced _________ Spectator Ion ________
O-2
Ca+2
NONE +3 -1 +2 -1
Mg0
NO3-
Au+3

13. IV. Identifying the Oxidized and Reduced AGENTS
reduction
Reducing Agent: causes ___________ (or is _____________)
Oxidizing Agent: causes ___________ (or is _____________)
For the following reactions, identify the oxidizing and reducing agent and spectator ion (if possible)
2 Li + F2  2 LiF
Oxidizing Agent _____ Reducing Agent _____
Spectator Ion ______
oxidized
oxidation
reduced
**AGENTS ALWAYS COME FROM THE REACTANT SIDE** +1 -1
ox.
red.
F20
Li0
NONE

14. IV. Identifying the Oxidized and Reduced AGENTS
2 MgO  2 Mg + O2
Oxidizing Agent_______ Reducing Agent _______
Spectator Ion ______
Ba + Sr(OH)2  Ba(OH)2 + Sr
Oxidizing Agent_______ Reducing Agent _______ Spectator Ion ______ +2 -2
red.
ox.
Mg+2
O-2
NONE +2 -1 +2 -1
ox.
red.
Sr+2
Ba0
OH-1

15. V. Half-Reactions oxidation reduction product lost reactant gained
A redox reaction may be split into 2 half-reactions, one for _______________ and the other for ____________________
Oxidation: X0  X+ + e-
X- X0 + e-
Reduction: X+ + e-  X0
X0 + e - X
oxidation
reduction
(e- on the _____________ side shows that it has been _______)
product
lost
reactant
(e- on the ____________ side shows that it has been_______)
gained

16. V. Half-Reactions +2 -2 red ox S -2  S0 + 2 e- Ca +2 + 2 e-  Ca0
For the following reactions, write the half-reactions:
CaS  Ca + S
Oxidation Reduction +2 -2
red ox
S -2  S0 + 2 e-
Ca e-  Ca0

17. V. Half-Reactions +2 -2 +2 -2 ox red Mg 0  Mg+2 + 2 e-
For the following reactions, write the half-reactions:
Mg + CuSO4  MgSO4 + Cu
Oxidation Reduction +2 -2 +2 -2 ox
red
Mg 0  Mg e-
Cu e-  Cu0

18. V. Half-Reactions +1 -1 +1 -1 red ox Na 0  Na+1 + 1 e- H + + e-  H 0
For the following reactions, write the half-reactions:
2 Na + 2HOH  2 NaOH + H2
Oxidation Reduction +1 -1 +1 -1
red ox
Na 0  Na e-
H + + e-  H 0

19. TOPIC 2: Electrochemistry
Objective: Predict which redox reactions will be spontaneous based on their position on the activity series table, identify the parts of a voltaic and electrolytic cell and describe their purpose, explain why the changes in concentration in each half cell are occurring as the reaction proceeds, and design a voltaic and electrolytic cell of your own.

21. I. Table F TOP MORE REACTIVE OXIDIZED (lose e-) REDUCED (gain e-)
The metal closer to the _________ of Table F are ____________________ and, therefore, more likely to be _________________. The nonmetals that are more reactive are more likely to be ______________________
Any ____________ on Table F will react ________________ with a ______________________ that is ______________________
This means that the metal with a charge must be_______________ the ____________________ metal for there to be a reaction
Activity Series ANIMATION
MORE REACTIVE
OXIDIZED (lose e-)
REDUCED (gain e-)
METAL
SPONTANEOUSLY
METAL ION
BELOW IT
BELOW
NEUTRAL

22. I. Table F
Example: According to Table J, which of the following will react spontaneously?
X + Co+  Co + X+
A) Pb +2 B) Sn+2 C) Fe D) H2
Example: Which of the following will replace Ni+2 in the compound Ni(NO3)2?
A) Sn +2 B) Pb+2 C) Sn D) Cr
Example: Which atom/ion pair will Co oxidize spontaneously under standard conditions?
A) Co + Fe B) Co + Pb+2 C) Co + Cu D) Co + Cr+3

23. II. Spontaneous Reactions on Voltaic Cells
Voltaic Cell - a redox reaction whose two half-reactions are carried out separately, and the electrons given off by the oxidation half-reaction are used to power a device, and then given to the reduction half-reaction. ALSO CALLED A BATTERY (9v) OR CELL (AAA, AA, C, D)
Voltaic Cell Animation
How a Voltaic Wet Cell Works:
Converts _____________ energy to ______________ energy by the use of a _______________________________ 
__________________ move from the metal that is ____________ to the metal that is _____________
Flow of electrons: ________________________________
CHEMICAL
ELECTRICAL
SPONTANEOUS REDOX REACTION
ELECTRONS
OXIDIZED
REDUCED
ANODE  CATHODE

24. II. Spontaneous Reactions on Voltaic Cells
Voltaic Cell - a redox reaction whose two half-reactions are carried out separately, and the electrons given off by the oxidation half-reaction are used to power a device, and then given to the reduction half-reaction. ALSO CALLED A BATTERY (9v) OR CELL (AAA, AA, C, D)
Voltaic Cell Animation and another set of animations: Complete Cell, Anode, Cathode, Salt Bridge

26. II. Spontaneous Reactions on Voltaic Cells
Parts of a Voltaic Wet Cell:
 Electrode:
Anode:
Cathode:
REMEMBER:
A PIECE OF METAL WHERE OX. OR RED. OCCURS
ELECTRODE WHERE OXIDITION OCCURS (SIZE ↓ )
ELECTRODE WHERE REDUCTION OCCURS (SIZE ↑ )
“RED CAT and AN OX”
REDUCTION OCCURS ON
CATHODE
ANODE HAS
OXIDATION

28. II. Spontaneous Reactions on Voltaic Cells
Salt Bridge:
External Circuit:
+ ions from bridge move into cathode half cell
-- ions from bridge move into anode half cell
Ions from the salt bridge flow to the solutions completing the circuit
Keeps the overall charge neutral in the half cells
WIRE THAT CONDUCTS THE e-

29. III. Nonspontaneous Reactions on Electrolytic Cells
Electrolytic Cell Animation

30. III. Nonspontaneous Reactions on Electrolytic Cells
Parts of an Electrolytic Cell:
Anode:
Cathode
Battery:
Electrolyte:
Flow of electrons:
Metal that is used to plate an object (+)
Metal that is being plated (--)
Produces energy to force nonspontaneous reaction to occur
Allow ions to flow between electrodes
e – start at anode and move toward the object being plated

31. X. Nonspontaneous Reactions on Electrolytic Cells
Electroplating (see electroplating video)

32. III. Nonspontaneous Reactions on Electrolytic Cells
Parts of a Electrolytic Cell:
Uses a ________________ redox reaction (the reaction _____________ occur on its own)
Uses ____________ to____________________
This process is called ________________________
Used for: 1) 2) 3)
nonspontaneous
will NOT
electricity
force a chemical reaction to occur
electrolysis
electroplating
Isolation of an element in a compound (NaClNa+Cl2)
Purification of an element

33. III. Nonspontaneous Reactions on Electrolytic Cells
The Car Battery (or rechargeable batteries) use both types of cells
Spontaneous Reaction to start the car
Nonspontaneous Reaction to charge the battery
VIDEO

34. IV. Similarities and Differences Between Voltaic and Electrolytic Cells
Similarities
“AN OX and RED CAT”
e – flow from anode to cathode
(+) ions flow toward the cathode, (--) ions flow toward the anode
Anode gets smaller, cathode gets larger

35. V. Differences Between Voltaic and Electrolytic Cells
____________________________
_____________________________
Anode is ____________________
Cathode is ___________________
Anode is ___________________
Cathode is ____________________
____________________ electricity
__________________ electricity
_________________ REACTION
__________________ REACTION
½ Reactions are for…
requires a battery
is an electric cell
negative
positive
positive
negative
USES
PRODUCES
SPONTANEOUS
NONSPONTANEOUS
Two different elements (two different solutions)
The same element (one solution both electrodes)