Oxidation

Reduction

Jinan Karameh Shayya

What does the word oxidation mean?

a. reaction with oxygen

b. losing electron during reaction

c. gaining electron during reaction

Engage

1. Name the materials used

in the first diagram

2. Describe what you see

in the second diagram?

3. Mg is oxidized. From this

reaction explain the meaning

of oxidation.

Explore

What does the word oxidation mean?

In ancient times, the word oxidation is related

to the reaction with oxygen. When an atom

reacts with oxygen it tends to lose electrons

and it is said to be oxidized. Now, all atoms

that lose electrons in a chemical reaction are

said to be oxidized or making oxidation.

Explain

It indicates if electrons are lost or gained by

an atom during a chemical reaction.

2Mg0 + O02 2 [ Mg+2 O-2]

Mg lost 2 electrons while Oxygen gained 2

electrons. The number above each atom/ion

is its oxidation number.

Oxidation Number

Rule 1: In its pure elemental form, an atom

has an oxidation number of zero

Oxidation number Rules

Rule 2: The oxidation number of an ion is the

same as its charge

Oxidation number Rules

Rule 3: The oxidation number of metals is +1

in group 1 and +2 in group 2

Oxidation number Rules

Rule 4: Hydrogen has two possible oxidation

numbers: +1 (if bonded with nonmetals) and

-1 (if bonded with metals)

Oxidation number Rules

Rule 5: Combined Al has oxidation number

+3, and combined F and Cl have oxidation

number -1 each.

Rule 6: Oxygen has oxidation number -2

except in peroxides it will be -1.

Oxidation number Rules

Rule 7: The algebraic sum of oxidation

numbers of atoms in a compound equals to

zero.

Rule 8: The algebraic sum of the oxidation

numbers of the atoms in a polyatomic ion

equals to its charge.

Oxidation number Rules

What is the oxidation state of chromium in

CrCl3?

This is a neutral compound so the sum of the oxidation

states is zero. Chlorine has an oxidation state of -1. If

the oxidation state of chromium is n:

n + 3(-1) = 0

n = +3 (Again, don't forget the + sign!)

Apply

What is the oxidation state of chromium in

the dichromate ion, Cr2O72-?

The oxidation state of the oxygen is -2, and the sum of

the oxidation states is equal to the charge on the ion.

Don't forget that there are 2 chromium atoms present.

2n + 7(-2) = -2

n = +6

Apply

If an atom loses electrons, its oxidation number

increases, so we can say that this atom undergoes

oxidation.

If an atom gains electrons, its oxidation number

decreases, so we can say that the atom undergoes

reduction.

OIL RIG: Oxidation Is Loss; Reduction Is Gain (of

electrons).

Oxidation number

They are chemical reactions through which

atoms gain and lose electrons changing their

oxidation number after the chemical reaction.

Redox Reactions

Is the following reaction Redox reaction?

Mg + 2HCl MgCl2 + H2

0 +1 -1 +2 -1 0

Mg + 2HCl MgCl2 + H2

Mg loses 2 e

H gains 1 e

Then this reaction is redox reaction

Apply

Have ever thought that this occurs in living

cells??

Redox reactions occur in photosynthesis and

cellular respiration.

Extend

Consider the following reaction:

Fe2O3 + 3CO 2Fe + 3CO2

1. Determine the oxidation number of each of

Fe, O and C before and after the reaction.

2. Deduce if this reaction is a redox reaction.

Evaluate

Thank you