Embedded Files
Lesson Instructions
Lesson Instructions
Review the learning goals and success criteria for Topic 2b: Balancing Redox Reactions using the Half Reactions Method.
Review the minds on, action, and consolidation sections of the lesson, completing any tasks as outlined.
Complete the fill-in-the-blanks handouts that have been provided to you. They have been linked below.
Practice and apply what you've learned by completing the practice tasks outlined at the end of the lesson.
Learning Goals
Learning Goals
I am learning to ...
balance complex redox reactions using half reactions in aqueous solutions.
balance redox reactions in acidic and basic solutions.
Minds On
Minds On
REDOX in our Bodies!
REDOX in our Bodies!
Does this look familiar?
The oxidized form of the electron carrier (NAD+) is shown on the left and the reduced form (NADH) is shown on the right.
The nitrogenous base in NADH has one more hydrogen ion and two more electrons than in NAD+.
Read MORE on REDOX reactions in the body here.
Read MORE on REDOX reactions in the body here.
Action
Action
For more complex reactions, we can use either of two methods:
Oxidation Numbers Method (previous lesson)
Half Reactions Method (this lesson)
For redox reactions, the CHARGE must be balanced, in addition to each element.
BALANCING REDOX REACTIONS: HALF REACTIONS METHOD
BALANCING REDOX REACTIONS: HALF REACTIONS METHOD
Write the oxidation and reduction half reactions.
Balance elements other than O and H.
Balance each half-reaction: add H20 to balance oxygen; add H+ to balance the hydrogen (acidic conditions); add H+ and OH- to balance the hydrogen (in basic conditions).
Add electrons to balance charge.
Balance the electrons (charge).
Add the equations together.
Check your answer.
PRACTICE
PRACTICE
IMPORTANT
When balancing redox reactions, you MUST pay attention to the type of conditions (acidic or basic) as this will determine if you need to add hydrogen (H+) or hydroxide (OH-).
EXAMPLE 1.
EXAMPLE 1.
BALANCE THE FOLLOWING REDOX REACTION IN ACIDIC CONDITIONS.
ClO4- + NO2 → Cl- + NO3- (acidic)
ClO4- + NO2 → Cl- + NO3- (acidic)
EXAMPLE 2.
EXAMPLE 2.
BALANCE THE FOLLOWING REDOX REACTION IN BASIC CONDITIONS.
ClO- + CrO2- → Cl2 + CrO42- (basic)
ClO- + CrO2- → Cl2 + CrO42- (basic)
Consolidation
Consolidation
Attempt some of the questions below and then compare your answer with the solutions provided.
(1) Balance the following redox reaction.
a) Fe2+(aq) + Cr2O72-(aq) → Fe3+(aq) + Cr3+(aq) (in acidic solution) [Show Answer]
(2) Balance the following redox reactions in acidic solutions.
b) MnO4-(aq) + Br-(aq) → MnO2(s) + BrO3-(aq) [Show Answer]
c) I2(s) + OCl-(aq) → IO3-(aq) + Cl-(aq) [Show Answer]
d) Cr2O72-(aq) + C2O42-(aq) → Cr3+(aq) + CO2(g) [Show Answer]
e) Mn(s) + HNO3(aq) → Mn2+(aq) + NO2(g) [Show Answer]
(3) Balance the following redox reactions in basic solutions.
f) CrO42-(aq) + S2-(aq) → Cr(OH)3(s) + S(s) [Show Answer]
g) MnO4-(aq) + I-(aq) → MnO2(s) + IO3-(aq) [Show Answer]
h) H2O2(aq) + ClO4-(aq) → O2(g) + ClO2-(aq) [Show Answer]
i) S2-(aq) + I2(s) → SO42-(aq) + I-(aq) [Show Answer]
This lesson is now complete. Consolidate your learning by evaluating the self-check below and the assigned practice questions.
Self-Check
(This is a self-assessment of your learning – you do not need to submit this).Self-Check
How prepared am I to start my homework? Can I ...
balance complex redox reactions using half reactions in aqueous solutions?
balance redox reactions in acidic and basic solutions?
Practice
Practice
Using your textbook, complete the following questions:
p616 # 1, 2
p617 # 7-10
p630 #44, 45
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