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Redox Reactions
Redox Reactions
Reactants: Zn + I2
Product: Zn I2
Redox Equations:
At the conclusion of our time together,
you should be able to:
1. Define redox
2. Figure out oxidation numbers for any
element
3. Show the change in oxidation numbers in a
reaction
Little Known Phobias!
Vacatianoia
mental state created en route to one's vacation,
when someone asks whether anyone remembered
to turn off the iron!
What’s the Point ?
REDOX reactions are important in …
• Purifying metals
(e.g. Al, Na, Li)
C3H8O + CrO3 + H2SO4 
Cr2(SO4)3 + C3H6O + H2O
• Producing gases
(e.g. Cl2, O2, H2)
• Electroplating metals
•
Electrical production (batteries, fuel cells)
• Protecting metals from corrosion
• Balancing complex chemical equations
• Sensors and machines (e.g. pH meter)
What is Redox?




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REDOX stands for REDuction/OXidation
Oxidation is often thought of as a combination of
a substance with oxygen (rusting, burning)
Oxidation refers to a loss of electrons
Reduction refers to a gain of electrons
As a mnemonic remember LEO says GER
• Loss Electrons = Oxidation
• Gain Electrons = Reduction
To: Santa Re: Where Are My Gifts?!
Actual E-mails to EmailSanta.com

Pleease! Don’t bring me any new clothes.

Kayla, 9
Let’s See How You’re Doing??
Q- What is oxidation? What is reduction?
Represent each as a chemical equation.
oxidation
reduction
= loss of e– …
= gain of e– …
X 
X+ + e–
X + e–  X–
Q- Why is 2Na + Cl2  2NaCl considered a redox
reactions?
This involves the transfer of electrons. (Na has no
charge, the atoms in diatomic molecules have no
partial charge. After reaction the atoms have
different shares of the electrons because of
different EN values)
Let’s See How You’re Doing??
Q- Is it possible to oxidize a material without reducing
something else?
No. A lost e– is taken up by something else.
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Determination of Oxidizing and Reducing
Agents
I.
II.
Determine oxidation # for all
atoms in both the reactants and
products.
Look at the same atom in
reactants and products and see
if oxidation # increased or
decreased.

If oxidation # decreased;
substance reduced

If oxidation # increased;
substance oxidized
Determination of Oxidizing and Reducing
Agents (continued)


Oxidizing Agent: Substance that
oxidizes the other substance by
accepting electrons. It is reduced
in reaction.
Reducing Agent: Substance that
reduces the other substance by
donating electrons. It is oxidized in
reaction.
Let’s See How You’re Doing??
Q- Define oxidizing agent, reducing
agent.
An oxidizing agent causes oxidation
by being reduced itself
A reducing agent causes reduction by
being oxidized itself
Review of Oxidation Numbers

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We will see that there is a simple way to keep track
of oxidation and reduction
This is done via “oxidation numbers”
An oxidation number is the charge an atom would
have if electrons in its bonds belonged completely to
the more electronegative atom
e.g. in HCl, Cl has a higher EN. Thus, oxidation
numbers are Cl = -1, H = +1
Notice that oxidation numbers are written as +1 vs.
1+ to distinguish them from charges.
Oxidation Numbers Rules
1. Any element, when not combined with atoms of a
different element, has an oxidation # of zero.
(O in O2 is zero, Na by itself is zero)
2. Any simple monatomic ion (one-atom ion) has an
oxidation number equal to its charge
(Na+ is +1, O2– is –2)
3. The sum of the oxidation numbers of all of the
atoms in a formula must equal the charge written
for the formula. (if the oxidation number of O is –2,
then in CO2 the oxidation number of C is +4)
Oxidation Number Rules
4. In compounds, the oxidation # of IA metals is +1,
IIA is +2, IIIA is +3, 13 is +3, Zn & Cd is +2,
Ag is +1.
5. In ionic compounds, the oxidation # of a
nonmetal or polyatomic ion is equal to the charge
of its associated ion.
(MgCl2, Mg is +2, therefore Cl is –1)
6. F is always –1, O is always –2
(unless combined with F),
H is usually +1, except when it is
bonded to metals in binary compounds.
(ex. NaH, H oxidation # is –1 or when it’s in
elemental form H2, oxidation # is 0).
Oxidation numbers
of all the elements
in the following ?
NaIO3
Na = +1 O = -2
3x(-2) + 1 + ? = 0
I = +5
IF7
F = -1
7x(-1) + ? = 0
I = +7
What Kind Of Coffee Was
Served On The Titanic?
Sanka.
Redox Equations:
Let’s see if you can:
1. Define redox
2. Figure out oxidation numbers for any
element
3. Show the change in oxidation numbers in a
reaction
Septic Tank Humor
Yesterdays
Meals on
Wheels
Let’s Apply the Oxidation Rules
or rule 5
Rule 6 3 6 4 3 6 3 6 6 4 5 6 3 6
Total +1 +5 -6 +2 +12 -14 -4 +6 -2 +1 -1 +2 +5 -8
Ox.# +1 +5 -2 +1 +6 -2 -2 +1 -2 +1 -1 +1 +5 -2
H N O 3 K2Cr2O7
C2H6O
AgI
H2PO4–
Familiar Saying
Glucose reveries.
Sugar high!!
Corrosion – Deterioration of Metals by
Electrochemical Process
Let’s consider
what happened to
the iron ribbing of
the Statue of
Liberty
Iron loses
e-,
therefore
is the
reducing
agent
Iron loses e-, therefore is oxidized
Oxygen gaines e-, therefore is reduced
Oxygen
gaines e-,
therefore
is the
oxidizing
agent
Corrosion – Deterioration of Metals by
Electrochemical Process
Determine and balance the
reaction, determine what is
oxidized and what is reduced.
Corrosion of Silver
Ag + O2  Ag2O
4 Ag + O2  2 Ag2O
Each Ag loses 1eEach O gains 2eSilver
Oxygen
Silver
Oxygen
=
=
=
=
oxidized
reduced
reducing agent
oxidizing agent
Hey, We’re Done, That’s Something to
Cheer About!!!
Redox Reactions
Things my moTher TaughT me…
IRONY.
"Keep crying, and I'll give you
something to cry about."
Redox Equations:
At the conclusion of our time together,
you should be able to:
1. Review redox
2. Review oxidation numbers for any element
3. Show the change in oxidation numbers in a
reaction and show the reaction
What is Redox?





REDOX stands for REDuction/OXidation
Oxidation is often thought of as a combination of
a substance with oxygen (rusting, burning)
Oxidation refers to a loss of electrons
Reduction refers to a gain of electrons
As a mnemonic remember LEO says GER
• Loss Electrons = Oxidation
• Gain Electrons = Reduction
Let’s See How You’re Doing??
Q- What is oxidation? What is reduction?
Represent each as a chemical equation.
oxidation
= loss of e– … X 
X+ + e–
reduction
= gain of e– … X + e–  X–
Q- Why is 2Na + Cl2  2NaCl considered a redox
reactions?
This involves the transfer of electrons.
The oxidation numbers change for 2 elements.
Na goes from 0 to
+1
Cl goes from 0 to
-1
Interesting Answers to Catholic
Elementary School Bible Questions:
Solomon, one of David’s
sons, had 300 wives and
700 porcupines.
Let’s See How You’re Doing??
Q- Is it possible to oxidize a material without reducing
something else?
No. A lost e– is taken up by something else.
Redox Reactions
Reactants: Zn + I2
Product: Zn I2
Redox Reactions
Reactants: Zn + I2
Each Zn loses 2eEach I gains 1eZinc
Iodine
Zinc
Iodine
=
=
=
=
oxidized
reduced
reducing agent
oxidizing agent
Product: Zn I2
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These are statements people actually said in
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published by court reporters.
ATTORNEY: What was the first thing
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WITNESS:
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ATTORNEY: And why did that upset
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WITNESS:
My name is Susan!