1. Introduction to Electrochemistry
Quick Video

2. LEO GER
Lose Electron – Oxidation
Gain Electron – Reduction

3. Oxidation – Reduction Reactions
Redox (oxidation – reduction reactions)
Electrons are transferred in reaction
Oxidation is always paired with reduction
Oxidation
Atom has lost an electron
LEO
Occurs at the anode
Reduction
Atom has gained an electron
GER
Occurs at the cathode
Oxidation Numbers
Also called oxidation states
Used to keep track of electrons

4. Rules for Assigning Oxidation Numbers
Atoms in elemental form always have oxidation number of zero
For any monatomic ion the oxidation number equals the charge on the ion
Oxidation number of oxygen is usually –2
Oxidation number of hydrogen is +1 when bonded to nonmetals
Oxidation number of hydrogen is –1 when bonded to metals

5. Oxidation number of fluorine is always –1
Oxidation number of halogens is –1 in binary compounds
The sum of the oxidation numbers in neutral compounds must be 0
The sum of the oxidation numbers in an ion equals the net charge on the ion.

6. P2O5 NaH Cr2O72- SnBr2 Examples
Assign the oxidation numbers for each of the elements
P2O5
NaH
Cr2O72-
SnBr2

7. 20.3 – Voltaic Cells (Galvanic Cells)
Electrons move from one cell to another to produce current
Anode
the electrode where oxidation occurs (loss of electrons)
always assigned “–“ charge
Cathode
the electrode where reduction occurs (gain of electrons)
always assigned the “+” charge

8. Current or electrons always flows from the anode to the cathode
Half – cell – compartment where oxidation or reduction happens
Salt bridge – porous disc which allows migration of ions so solutions remain electrically neutral

9. A video overview of Voltaic (galvanic cells)

11. Identify what is being oxidized and what is being reduced
Cd(s) NiO2 (s) H2O (l)  Cd(OH)2(s) Ni(OH)2 (s)
2 H2O (l) Al (s) MnO4- (aq)  Al(OH)4- (aq) MnO2 (s)

12. Cr2O72- (aq) Cl- (aq)  Cr3+ (aq) Cl2 (g)

13. Cu (s) + NO3- (aq)  Cu2+ (aq) + NO2 (g)

14. NO2- (aq) + Al (s)  NH3 (aq) + Al(OH)4-

15. ClO3- (aq) + 6H+ (aq) + 6 e-  Cl-(aq) + 3 H2O (l)
Example
The two half reaction in a voltaic cell are:
Zn (s)  Zn2+ (aq) e-
ClO3- (aq) H+ (aq) e-  Cl-(aq) H2O (l)
Indicate which reaction occurs at the anode and at the cathode.
Which electrode is consumed in the cell reaction?
Which electrode is positive?