General Chemistry 2
Quarter 4
Module 5: Redox Reactions
Prepared by:
Jasmine D. Colcol
Let’s review!
What are atoms made of?
• Protons
• Electrons
• Neutron
Did I Lose or Gain?
Decide whether the given half-reaction
involves the lose or gain of electrons.
Did I Lose or Gain?
Li
(s)
Li
+
(aq)
Did I Lose or Gain?
S
(s)
S
2(aq)
Did I Lose or Gain?
Cr
3+
(aq)
Cr
2+
(aq)
Did I Lose or Gain?
Cu
Cu
2+
Did I Lose or Gain?
Na
Na
1+
General Chemistry 2
Quarter 4
Module 5: Redox Reactions
Prepared by:
Jasmine D. Colcol
General Chemistry 2
Quarter 4
Redox Reactions
Prepared by:
Jasmine D. Colcol
Learning Competencies:
o Define oxidation-reduction reactions. (STEM_GC11AB-lvf-g-169)
o Balance redox reactions using the change in oxidation number
half-reaction method. (STEM_GC11AB-lvf-g-170)
o Subtasks:
o Assign oxidation states to elements
o Recognize the importance of the lesson to life.
Redox Reactions
• Redox reactions stand for oxidation-reduction
reactions.
• Redox reactions describe all chemical reactions
in which there is a net change in atomic charge
Redox Reactions
Reduction (charge decreases)
Oxidation (charge increases)
Redox Reactions
Redox Reactions
Oxidation Number
It is a concept that helps in determining quickly whether
the substance is undergoing oxidation or reduction. Other
terms used to refer to oxidation number is valence or
oxidation state. Oxidation states is the electrical charge
assigned to an atom according to a prescribed set of rules.
General Rules in Assigning Oxidation Number
1. The oxidation
state of a free and
uncombined
element is zero.
Li
(s)
N2
General Rules in Assigning Oxidation Number
2. For a monatomic ion:
oxidation number = ion charge
Cu
2+
General Rules in Assigning Oxidation Number
3. The sum of oxidation number
values for the atoms in a
molecule or formula unit of a
compound equals to zero.
(and equals to the ion’s charge if
it is a polyatomic ion)
H2O
NH41+
General Rules in Assigning Oxidation Number
The usual oxidation state of:
a. Hydrogen is +1, except in metallic hydrides ( Li+1H-1 )
b. Oxygen is -2, except in peroxides where it is -1 ( H2+1O2 -1 )
c. Elements under
group IA is +1 (Na+1)
IIA is +2 (Mg+2)
IIIA is +3 (Al+3)
Know my State!
Determine the oxidation number of each element in the ff:
1. CaO
2. KNO3
Know my State!
Determine the oxidation number of each element in the ff:
3. H2O2
4. O3
Know my State!
Determine the oxidation number of each element in the ff:
5. S2O7
-2
Let’s Practice!
Identify the material being reduced, the material being oxidized, the
reducing agent, and the oxidizing agent in each of the following
redox reactions:
2Cs + Br2 → 2CsBr
substance reduced: ____________
substance oxidized: ____________
oxidizing agent: ____________
reducing agent: ____________
Let’s Practice!
Identify the material being reduced, the material being oxidized, the
reducing agent, and the oxidizing agent in each of the following
redox reactions:
2Sr + O2 → 2SrO
substance reduced: ____________
substance oxidized: ____________
oxidizing agent: ____________
reducing agent: ____________
Let’s Practice!
Identify the material being reduced, the material being oxidized, the
reducing agent, and the oxidizing agent in each of the following
redox reactions:
Si + 2F2 → SiF4
substance reduced: ____________
substance oxidized: ____________
oxidizing agent: ____________
reducing agent: ____________
Redox Half-Reactions
• Redox reactions can be broken up into oxidation
& reduction half reactions.
2+
2+
Pb (aq) + Zn(s) → Pb(s) + Zn (aq)
Reduction Half-rx: Pb2+(aq) + 2e- → Pb(s)
Oxidation Half-rx: Zn(s) → Zn2+ (aq) + 2e-
Redox Half-Reactions
• Redox reactions can be broken up into oxidation
& reduction half reactions.
2+
2+
Pb (aq) + Zn(s) → Pb(s) + Zn (aq)
Reduction Half-rx: Pb2+(aq) + 2e- → Pb(s)
Oxidation Half-rx: Zn(s) → Zn2+ (aq) + 2e-
Redox Half-Reactions
• Redox reactions can be broken up into oxidation
& reduction half reactions.
2+
2+
Pb (aq) + Zn(s) → Pb(s) + Zn (aq)
Reduction Half-rx: Pb2+(aq) + 2e- → Pb(s)
Oxidation Half-rx: Zn(s) → Zn2+ (aq) + 2e-
Let’s Practice!
Identify each of the following as examples of oxidation or reduction:
▪ Li(s)
▪ S(s)
▪
+
→ Li
(aq)
+e
2+ 2e → S
3+
Cr
(aq)
(aq)
2+
+ e → Cr
(aq)