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8/2/2019 RedOx Rxns - Teaching Demo.pptx
1/19
Oxidation-Reduction
(RedOx) Reactions
Prepared by:
Julius Victorius A. Saluria
8/2/2019 RedOx Rxns - Teaching Demo.pptx
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What is a RedOx reaction?
A type of reaction thatinvolves TRANSFEROF ELECTRON(S)
between two species Composed of a
REDUCTION andOXIDATION half
reactions NO NET CHANGE in
the number of electrons
8/2/2019 RedOx Rxns - Teaching Demo.pptx
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Lets Review: Oxidation Number (ON)
A number assigned to an element in a moleculeor ion that describes its oxidation state
1. Elements in elementary substance has ON = 0.
Example: Br2(l), P4(s), O2(g), Cu(s)
2. The charge of a monatomic ion is the ON of
that element
Example: Fe3+ (ON=+3), S2- (ON=-2)
8/2/2019 RedOx Rxns - Teaching Demo.pptx
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Lets Review: Oxidation Number (ON)
3. The sum of ON of the atoms in a neutral species iszero; in a polyatomic ion, it is equal to the charge
of that ion
Example: H2O (ON of H=+1, ON of O=-2)
2(+1) + 1(-2) = 0
AlCl4- (ON of Al=+3, ON of Cl=-1)
1(+3) + 4(-1) = -1
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4. Certain elements have the same oxidation
number in all or almost all their compounds
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Lets Review: Oxidation Number (ON)We can determine the oxidation number of an element in
a compound/polyatomic ion.
i.e. What is the oxidation number of S in SO42-?
Let x be the ON of S
Charge of ion = sum of the ON of the elements in thecompound/polyatomic ion
-2 = 1(x) + 4(ON of O)
-2 = x + 4(-2)
-2 = x8
x = +6
Therefore, S has an ON of +6
8/2/2019 RedOx Rxns - Teaching Demo.pptx
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Oxidation
Half-reaction in which
the species
INCREASES (morepositive) in oxidation
number
The electron is found onthe PRODUCT SIDE of
the chemical equation of
the half-reaction
8/2/2019 RedOx Rxns - Teaching Demo.pptx
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8/2/2019 RedOx Rxns - Teaching Demo.pptx
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Reduction
Half-reaction in which
the species
DECREASES (less
positive) in oxidation
number
The electron is found on
the REACTANT SIDE
of the chemical equation
of the half-reaction
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8/2/2019 RedOx Rxns - Teaching Demo.pptx
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Balancing Half Reactions
Balance the atoms of the element that gets reduced
or oxidized.
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Balancing Half Reactions
Balance the O atom by adding H2O to theO-deficient side.
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Balancing Half Reactions
Balance the number of H atoms by adding H+ to the H-deficient side. If balancing half reactions in basic
solution, add OH- to both sides of equation equal tothe number of H+ previously added.
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Balancing Half Reactions
Lastly, balance the charge by adding electrons.
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Balancing RedOx Reactions
Split the equation into two half equations.
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Balancing RedOx Reactions
Balance each half reactions. From this step, you willnow be able to determine which of the species isreduced and which one is oxidized.
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Balancing RedOx Reactions
Combine the half equations in such a way that theelectrons in the equation are eliminated.
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Balancing RedOx Reactions
Simplify the equation by cancelling species thatappear on both sides of the equation.
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Lets Practice!1. Determine the oxidation number of I in the
following compounds:
a. IO-(aq) b. NaI(s) c. I2(s)
2. Balance these half reactions and determine whetherthe reaction is oxidation or reduction:
a. Ni2+(g) Ni2O3(s) (in basic solution)b. ClO-(aq) ClO2
-(aq) (in acidic solution)
3. Balance this RedOx reaction in basic medium anddetermine which is the oxidizing and reducingagent:
K(s) + H2O(l) K+
(aq) + H2(g)