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Oxidation, Reduction, and Redox Reactions

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Nita Rafshi

on 5 March 2015

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Transcript of Oxidation, Reduction, and Redox Reactions

Reactants and Their
Agents
Redox Reaction Rules
All individual chemicals have an oxidation of zero.
Redox Reactions
These reactions are exothermic, meaning they produce heat energy.
Redox reactions are have many similarities to acid-base reactions.
They are a family of reactions that involve the transfer of electrons between elements.
With these reactions, it is essential to keep track of the electrons to know whether a reduction or oxidation reaction is occurring.

Redox Reaction Rules
Rule #2
: Oxidation state= the charge of the ion.
Redox Reaction Rules
Oxygen has an oxidation state of -2 unless it is in a provided molecule, such as H O
Oxidation, Reduction Reactions
Redox Reactions

Redox Reaction
Example
2 3
What is Oxidation and Reduction?
Oxidation is the loss of electrons
Reduction is the gain of electrons
Redox is the name we call both reduction and oxidation reactions
Redox reactions are a combined set, thus meaning you cannot have a reduction reaction without a oxidation reaction.
Each reaction on its own is called a 'half reaction' or a 'half-cell reaction', which together creates a 'whole reaction'.
OIL RIG
O
xidation
I
s
L
oss of electrons
R
eduction
I
s
G
ain of electrons
Redox Reactions
In each reaction, both oxidation and reduction reactions are present.
Reducing Agent
Oxidation Agent
causes oxidation
is reduced
gains electron(s)
causes reduction
is oxidized
loses electron(s)
The reactant that is REDUCED is usually the oxidizing agent.
The reactant that is OXIDIZED is usually the reducing agent.
Fe 0 + 3C0
2Fe + 3C0
2
Reduction
Oxidation
-1
2
2
Redox Reaction Rules
Hydrogen has an oxidation state of +1
Redox Reaction Rules
Fluorine has an oxidation state of -1. Most other halogens have an oxidation state of -1, unless they're bonded to fluorine or oxygen.
Oxygen's oxidation
state= -2
Exception example: H O
2
2
-1
Hydrogen's Oxidation
state= +1
Fluorine's oxidation
state= -1
Hayleigh, Nita, Vasoula
Oxidation state = the charge of the ion.
Rule 1
Rule 2
Rule 3
Rule 4
Rule 5
Oxidation, Reduction
Redox Reactions
What are they?
Oxidation-reduction reactions are also called redox reactions: any chemical reaction in which the oxidation number of a participating chemical species changes.The term covers a large and diverse body of processes.
Redox Reaction Examples
Many Redox reactions are as common as fire, the rusting and dissolution of metals, the browning of fruit, respiration and photosynthesis.
Historical Significance
Oxidation originally implied reactions with oxygen, to form an oxide, since dioxide was historically the first recognized oxidizing agent. Later, the term was expanded to include oxygen like substances that accomplish parallel chemical reactions. The meaning was generalized to include all processes involving the loss of electrons.
Oxidation
Historical Significance
Reduction
Reduction originally referred to the loss in weight upon heating a metallic ore, such as a metal oxide to extract the metal. In other words, the ore was reduced to metal. Later, it was shown that the weight was due to the loss of oxygen as a gas. Scientists realized that the metal atom gains electrons in this process. The meaning of reduction then became generalized to include all processes involving gain of electrons.
Half Cell Reactions
A half reaction is either the oxidation or reduction reaction of a redox component. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Half reactions are used to describe what occurs in an electrochemical cell.
Examples of Half Cell Reactions
2
2
The Overall Reaction
(sum of both reactions)
2Mg(s)+O (g)
2MgO(s)
Oxidation Half Reaction (ANODE)
Original Reaction
2Mg(s)
2Mg +4e
2+
-
Reduction Half-Reaction (CATHODE)
O (g)+4e
2O
2-
2Mg(s)+O (g)
2
2Mg +2O
2
2-
The Final Reaction
2Mg(s)+O (g)+4e
2
-
2Mg + 2O +4e
2
-
Net-Ionic Equations
OXIDIZING REACTION + REDUCTION REACTION
REDOX REACTION
For Ionic reactions not all the chemical species undergo a change.Those that don't change are called Spectator Ions.
When spectator ions are removed from a chemical reaction they produce what is termed as a Net-Ionic reaction.
Steps to write the equations
Step 1
Step 2
Writing the Net Ionic
Balance the equations for atoms
Write out the dissolved chemical species as they exist in the solution.
Precipitates, liquids, and gases
ARE NOT
written as ions. This called a total ionic equation.
Remove common aqueous ions (ions that are in both the reactant and product). The resulting equation is called the net-ionic equation.
Place the formula for the ionic solid in the reactants
Place the formulas for the ions that compose the solid in products
Balance for the charge and atoms by changing the co-efficient of the products
Writing the dissolving of ionic solids
Write the formula equations and balance
Write the aqueous substances as separate ions. Leave solids, liquids and gases unchanged.
Cancel common aqueous ions (net ionic equations)

Half Cell Reactions Balancing Method
In Acidic Solutions
Step 1
-Divide the skeleton equation into half reactions
Step 2
-Balance atoms other than H and O
Step 3
-Balance oxygen atoms by adding O to the side that needs O
Step 4
-Balance hydrogen by adding H to the side that needs H
Step 5
-Balance the charge by adding electrons
Step 6
-Make the electrons gained equal to the electrons lost and then add the two half-reactions.
Step 7
-Cancel anything that is the same on both sides.
Step 8
-Add the same number of OH as there are H to both sides of the equation.
Step 9
-Combine OH as there are H to both sides to the equation.
Step 10
-Cancel any H O
2
In Basic Solutions from 8-10
2
Metallic ore
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