Introduction to Oxidation/Reduction Reactions
● Describe an Oxidation-Reduction reaction
○ Definition:
■ Oxidation-reduction (redox) reactions are chemical reactions in which
electrons are transferred from one reactant to another.
○ Key Processes:
■ Every redox reaction consists of two simultaneous processes:
● Oxidation:
○ An atom loses electrons, which increases its oxidation
number
● Reduction:
○ An atom gains electrons, which result in a decrease in its
oxidation number
● Rememeber
○ OIL RIG
■ Oxidation
■ IS
■ Loss
■ Reduction
■ Is
■ Gain
○ Agents:
■ Oxidizing Agent:
● The substance that causes the oxidation of another substance.
Because it gives electrons to something else, the reducing agent
itself is always oxidized.
■ Reducing Agent:
● The substance that causes the reduction of another substance.
Because it gives electrons to something else, the reducing agent
itself is always oxidized.
● Calculate Oxidation Numbers
○ An oxidation number (or state) is the theoretical charge an atom would take if all
shared electrons in a compound were completely assigned to the atom with the
stronger attraction for those electrons.
○ Calculated by hierarchical rules, if rules conflict, prioritize the rule higher on the
list
■ 1. Free Elements:
● The oxidation state of any atom in a free, uncombined element is
always 0
○ Example: Cu or Cl
■ 2. Monoatomic Ions:
● The oxidation state is equal to the exact charge of the ion
○ Example: Ca2+ is +2
■ 3. Sum of Oxidation states:
, ● In a neutral molecule, the sum of all oxidation states must equal 0.
○ In a polyatomic ion, the sum of all oxidation states must
equal the charge of the ion
○ You must multiply the atoms oxidation state by the number
of atoms present in the formula (H2O: 2(H)+1(O)=0)
■ 4. Metals in Compounds
● Metals always have positive states
○ Group 1A metals always have an oxidation state of +1
○ Group 2A metals always have an oxidation state of +2
■ 5. Nonmetals in Compounds:
● Nonmetals are assigned states using the specific priority table
below (elements at the top take priority over those below)
○
Nonmetal Element Assigned Oxidation State
Fluorine -1
Hydrogen +1
Oxygen -2
Group 7A (Halogens) -1
Group 6A -2
Group 5A -3
○ When dealing with elements that do not have fixed rules,
like carbon, assign the high-priority elements first, and use
Rule 3 to deduce the remaining unknown oxidation state
● Use Oxidation Numbers to Identify a Redox Reaction
○ To determine if a chemical reaction is a redox reaction, use a two-step method:
■ Assign Oxidation numbers to every single atom on both the reactant side
and the product side
■ Compare the values. If there is a change in the oxidation number of any
atom from the reactant side to the product side, a redox reaction is
occurring.
○ Example: Consider the reaction of solid magnesium with water
■ Mg(s) + 2H2O(l) → Mg (OH)2(aq) + H2(g)
● Step 1: Assign Oxidation States:
○ Reactants:
■ Mg = 0 (free element); H = +1 and O = -2 in (H2O)
○ Products:
■ Mg= +2 and O =-2, H = +1 (in Mg(OH)2; H=O (in
free element H2
● Step 2: Identify Changes
● Describe an Oxidation-Reduction reaction
○ Definition:
■ Oxidation-reduction (redox) reactions are chemical reactions in which
electrons are transferred from one reactant to another.
○ Key Processes:
■ Every redox reaction consists of two simultaneous processes:
● Oxidation:
○ An atom loses electrons, which increases its oxidation
number
● Reduction:
○ An atom gains electrons, which result in a decrease in its
oxidation number
● Rememeber
○ OIL RIG
■ Oxidation
■ IS
■ Loss
■ Reduction
■ Is
■ Gain
○ Agents:
■ Oxidizing Agent:
● The substance that causes the oxidation of another substance.
Because it gives electrons to something else, the reducing agent
itself is always oxidized.
■ Reducing Agent:
● The substance that causes the reduction of another substance.
Because it gives electrons to something else, the reducing agent
itself is always oxidized.
● Calculate Oxidation Numbers
○ An oxidation number (or state) is the theoretical charge an atom would take if all
shared electrons in a compound were completely assigned to the atom with the
stronger attraction for those electrons.
○ Calculated by hierarchical rules, if rules conflict, prioritize the rule higher on the
list
■ 1. Free Elements:
● The oxidation state of any atom in a free, uncombined element is
always 0
○ Example: Cu or Cl
■ 2. Monoatomic Ions:
● The oxidation state is equal to the exact charge of the ion
○ Example: Ca2+ is +2
■ 3. Sum of Oxidation states:
, ● In a neutral molecule, the sum of all oxidation states must equal 0.
○ In a polyatomic ion, the sum of all oxidation states must
equal the charge of the ion
○ You must multiply the atoms oxidation state by the number
of atoms present in the formula (H2O: 2(H)+1(O)=0)
■ 4. Metals in Compounds
● Metals always have positive states
○ Group 1A metals always have an oxidation state of +1
○ Group 2A metals always have an oxidation state of +2
■ 5. Nonmetals in Compounds:
● Nonmetals are assigned states using the specific priority table
below (elements at the top take priority over those below)
○
Nonmetal Element Assigned Oxidation State
Fluorine -1
Hydrogen +1
Oxygen -2
Group 7A (Halogens) -1
Group 6A -2
Group 5A -3
○ When dealing with elements that do not have fixed rules,
like carbon, assign the high-priority elements first, and use
Rule 3 to deduce the remaining unknown oxidation state
● Use Oxidation Numbers to Identify a Redox Reaction
○ To determine if a chemical reaction is a redox reaction, use a two-step method:
■ Assign Oxidation numbers to every single atom on both the reactant side
and the product side
■ Compare the values. If there is a change in the oxidation number of any
atom from the reactant side to the product side, a redox reaction is
occurring.
○ Example: Consider the reaction of solid magnesium with water
■ Mg(s) + 2H2O(l) → Mg (OH)2(aq) + H2(g)
● Step 1: Assign Oxidation States:
○ Reactants:
■ Mg = 0 (free element); H = +1 and O = -2 in (H2O)
○ Products:
■ Mg= +2 and O =-2, H = +1 (in Mg(OH)2; H=O (in
free element H2
● Step 2: Identify Changes
