1. Chapter 20: LEO the lion goes GER
OXIDATION AND REDUCTION REACTIONS

2. RULES FOR ASSIGNING OXIDATION NUMBERS
1. EQUAL TO IONIC CHARGE
EX: NaCl = Na+1 Cl-1
Except in H2O2 (H+1 and O-1)
2. HYDROGEN IS ALMOST ALWAYS +1
EXCEPT ALKALI METALS-HYDRIDES (NaH, LiH)
3. OXIDATION # OF AN UNCOMBINED
ELEMENT IS ALWAYS ZERO
EX: Mg = Mg0

3. RULES FOR ASSIGNING OXIDATION NUMBERS
4. SUM OF ALL OXIDATION #S MUST
EQUAL ZERO IN A COMPOUND
EX: NH3 = N-3 H3+1
FOR POLYATOMIC IONS, OXID. #
MUST = THE CHARGE OF THE ION
EX: (SO4)-2 = S+6 O4-2
(+6)+ -8 = -2

4. LEO the lion …… Oxidation:
the combination of an element with oxygen (gain of oxygen).
EX: 4 Fe(s) + 3O2(g) Fe2O3(s)
Iron lost electrons = oxidized
EX: Mg + S MgS
Substance that loses e-s is the
Reducing Agent (reducing in size b/c of loss of electrons)

5. Oxidized = Reducing Agent
The substance that is
oxidized is the reducing agent
Mg + S MgS
Mg is OXIDIZED +2
Reducing Agent

6. ……goes GER Reduction: the loss of oxygen
EX: 2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)
Fe gains electrons =reduced
EX: Mg + S MgS
Substance that accepts e-s is an
Oxidizing Agent

7. Reduced = Oxidizing Agent
The substance that is
reduced is the oxidizing agent
Mg + S MgS
S is REDUCED -2
Oxidizing Agent