Redox Reactions
Lesson five
CA Science Content
Standards:
drawing the flow of electrons during a
Chemistry: Conservation of
Matter and Stoichiometry
be able to balance basic redox reactions.
3.a D
escribe chemical
reactions by writing
balanced equations.
3.g I dentify reactions that
involve oxidation and
reduction and how
to balance oxidationreduction reactions.
of oxidation/reduction reactions by
redox reaction in a battery. They will also
Students will explain how more reactive
metals lose their electrons and less reactive
metals keep their electrons by reading a
reduction potential sheet. The students
Redox Reactions
Students will demonstrate understanding
Lesson 5
Terminal Objective
will be able to explain how these concepts
Materials
Redox Reactions Powerpoint
ships.
Time Required
1 class
apply to the use of zinc underneath cargo
Redox Reactions
| 45
Introduction of Lesson
The Port of Long Beach is the second largest port
in the United States, only slightly smaller than its
neighbor the Port of Los Angeles.
anode
cathode
electricity
corrosion / corrode
electrolyte
electrolytic solution
reduction
oxidation
redox
Redox Reactions
Lesson 5
Key Vocabulary
The Port of Long Beach serves huge ocean-going
cargo ships importing and exporting more than
$140 billion worth of goods each year. Transporting
this volume of goods yearly requires thousands of
ships sailing across the oceans every year. These
ships are sailing through very corrosive salt water
which corrodes the outer iron hulls, oxidizing the
iron into rust.
Steps are taken to keep the cargo ships from
rusting. Large pieces of zinc, which is more
reactive than iron, are placed on the propeller shaft
and outside of the hull so that oxidation will occur
to the zinc and less so with the iron. So, instead
of replacing entire hulls of ships which would be
extremely expensive, zinc anodes are used which
oxidize and are easily replaced at a fraction of the
cost.
Anticipatory Set:
Say to the students:
“Who has ever seen the huge cargo ships out on
the water just outside Long Beach? What are they
doing there?”
“What happens to iron, like a nail or screw, if
you just leave it sitting outside for a week or two?
Let’s quickly review from what we have learned
about redox reactions, and again explain how rust
occurs.”
46 | Redox Reactions
“Well, boats are made out of iron, their propellers
are also, and guess what happens if you leave them
in water for a long time? If the ocean-going cargo
ships are 20 years old, does anyone have an idea of
how they aren’t all rusted away?”
Lesson
For teachers:
There are two main factors that keep ships from
rusting:
• paint protection – shields the metal, keeping iron
from coming in direct contact with ocean water
• cathodic protection – use of a reactive metal like
zinc that will lose its electrons more readily than
iron when placed in the water
Input:
Using the Redox Reactions PowerPoint, provide
background.
Redox Reactions
Lesson 5
When two metals are submerged into an
electrolytic solution and touched together,
electricity is produced by flowing electrons out of
one of the metals. You can see the propeller has lost
some of its metal.
To keep the metal in the propeller from corroding,
the reactive metal of zinc is oxidized and turned
into ions, instead of the propeller.
About redox reactions:
• Redox reactions occur when there is a gain and
loss of electrons from different reactants.
• Reduction and oxidation go hand in hand.
• If one compound loses 10e-, than another has to
gain 10e-.
• The following reactions show metals reacting and
exchanging electrons with each other and with
non-metals:
For instance, if you put copper metal into a solution
of silver nitrate (AgNO3), you will see the copper
begin to dissolve as dark silver solid begins to
appear.
For redox reactions, start with half of the reaction
at a time.
Redox Reactions
| 47
Lesson cont’d
Copper loses electrons:
Cu(s) → Cu2+(aq) + 2eSilver ions pick up electrons:
Cu(s) → Cu2+(aq) + 2eAg+ (aq) + e- → Ag(s)
Balance the electrons:
Cu(s) → Cu2+(aq) + 2e2 Ag+ (aq) + 2e- → 2Ag(s)
____________________________________
Lesson 5
Add together:
Cu(s) → Cu2+(aq) + 2e-
2 Ag+ (aq) + 2e- → 2Ag(s)
Redox Reactions
2Ag+ (aq) + Cu(s) → 2Ag(s) + Cu2+(aq)
Electrons were gained by the Ag and lost by the Cu.
The Ag was reduced and the Cu was oxidized.
Even aluminum can “rust” or oxidize.
This is a redox reaction, because any time
something gets oxidized, something else must be
reduced. (The electrons have to go somewhere!)
How many electrons transfer in each half reaction?
How many electrons in each half reaction?
Al(s) → Al3+(aq) +eO2(g) + e- → 2O2-(aq)
Balance the electrons:
4[Al(s) → Al3+(aq) + 3e- ]
3[O2(g) + e- → 2O2-(aq)]
3O2(g) + 4Al(s) → 4Al3+(aq) + 6O2-(aq) ]
48 | Redox Reactions
Lesson cont’d
Cadmium ripping off iron’s electrons:
Fe0 → Fe2+2e-
2e- + Cd2+ → Cd0
Cd2+ + Fe0 → Fe2+ + Cd0
Our trouble-making reaction. Iron going to rust:
4[Fe0 → Fe3 + 3e-]
3[4e- + O2 → 2O2-]
4 Fe0+ 3O2 → 4Fe3+ + 6O2-
→ 2Fe2O3(s) (RUST)
Redox Reactions
Lesson 5
• Students should balance additional redox
reactions and research where some of those
chemical reactions actually take place and matter.
• Demonstrate or have students make electrolytic
cells as shown on the last presentation slide. This
is a great way to give the students a hands-on
experience and see how simple a battery really is.
Culminating Activity
• Have the students draw a circuit with a light bulb
and a battery which has an aluminum anode
and a cadmium cathode. Have them draw and
explain why the electrons move through the
light in the direction they do (use the standard
reduction potentials chart).
• Have students write a tie-in back to the idea of the
ships in the port and why they use a zinc anode
with the iron ships so that the iron doesn’t wear
away so quickly.
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