1. Unit 6: Electrochemistry

2. Redox Reactions Redox is short for ‘oxidation and reduction’
Oxidation refers to substances that combine with oxygen
Iron rusting, campfire burning
Reduction refers to converting metal ore to pure metal
Oxidation-reduction reactions are reactions that exchange electrons (one loses and one gains them)

3. Demo Copper wire in silver nitrate Ionic Equation
Cu(s) + 2AgNO3(aq) Cu(NO3)2 (aq) + 2 Ag(s)
Ionic Equation
Cu(s) + 2Ag+(aq) + 2NO3-(aq) → Cu2+(aq) + 2NO3-(aq) + 2Ag(s)
Overall Net Ionic Equation
Cu(s) + 2Ag+(aq) → Cu2+(aq) + 2Ag(s)
What changed?

4. Oxidation
the loss of electrons
Reduction
the gaining of electrons
One can’t happen without the other

6. LEO GER LEO Loss of Electrons is Oxidation the Lion Says GER GER
Gain of Electrons is Reduction

7. OXIDATION NUMBERS
Electrons are transferred from one substance to another
We use oxidation numbers aka electronegativity to track this
Electronegativity
The ability of a bonded atom to attract shared electrons towards itself
Oxidation Numbers
A positive or negative number assigned to an atom in a molecule or ion that reflects a partial gain or loss of electrons

8. nOTES
The oxidation number of a pure element (by itself, and not an ion) is zero
Element
Oxidation Number Na H2 O2
P4 

9. 2. Oxidation number of anion is equal to its charge
Ionic Compound
Ions
Charge
Oxidation Number
NaCl
Na+ +1
Cl- -1
Mg3N2
Mg+2 +2
N-3 -3

10. 3. oxidation number is hydrogen is always +1
Compound
element
Oxidation Number
HCl H +1 Cl -1
H2S S -2

11. 4. Oxidation number is oxygen is almost always -2
Compound
element
Oxidation Number
MgO
magnesium oxide Mg +2 O -2
Na2O
sodium oxide Na +1
Na2O2
sodium peroxide -1
The exceptions:
peroxides, such as hydrogen peroxide. In peroxides oxygen has an oxidation number of -1.
when oxygen is combined with fluorine it's oxidation number is +2

12. 5. sum of oxidation numbers in a compound is zero
element
Oxidation Number
Number atoms
Total
Mg3N2 Mg +2 3 +6 N -3 2 -6
SUM
Mn2O7 Mn +7
+14 O -2 7
-14
Cl2O3 Cl +3

13. 6. oxidation number of polyatomic ions are equal to it’s charge
Compound
element
Oxidation Number
Number atoms
Total
NO3- N +5 1 O -2 3 -6
SUM -1
Cr2O72- Cr +6 2
+12 7
-14
SO42- S 4 -8

14. It is important to note that oxidation number always refers to each individual atom in the compound, not to the total for that element.
For example in H2O - the total positive "charge" for both hydrogen atoms will be +2 (which balances with the -2 from oxygen), but EACH HYDROGEN has an oxidation number of +1.

15. Practice problems 6.1.2- practice
Being able to determine oxidation numbers for elements in a compound is critical before you move on to the next step