redox rxns - teaching demo.pptx

8/2/2019 RedOx Rxns - Teaching Demo.pptx

1/19

Oxidation-Reduction

(RedOx) Reactions

Prepared by:

Julius Victorius A. Saluria


2/19

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


3/19

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)


4/19

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


5/19

4. Certain elements have the same oxidation

number in all or almost all their compounds


6/19

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


7/19

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


8/19


9/19

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


10/19


11/19

Balancing Half Reactions

Balance the atoms of the element that gets reduced

or oxidized.


12/19


Balance the O atom by adding H2O to theO-deficient side.


13/19


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.


14/19


Lastly, balance the charge by adding electrons.


15/19

Balancing RedOx Reactions

Split the equation into two half equations.


16/19


Balance each half reactions. From this step, you willnow be able to determine which of the species isreduced and which one is oxidized.


17/19


Combine the half equations in such a way that theelectrons in the equation are eliminated.


18/19


Simplify the equation by cancelling species thatappear on both sides of the equation.


19/19

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)

redox rxns - teaching demo.pptx

Documents