Redox Part 2

Redox Part 2

​1.     state and calculate the oxidation state of elements in a compound.

2.     define oxidation as an increase in oxidation state;

3.     define reduction as a decrease in oxidation state.

4.     identify redox reactions.
5. define an oxidising agent as a substance that causes another substance to be oxidised,
and a reducing agent as a substance that causes another substance to be reduced.

Objective of the day -
At the end of the lesson you should be able to

​B. Going through this video on youtube.

​A. Going through the powerpoint in Quizizz.

You have a Choice!!

​Complete the Quiz at the end of this segment.

Revision on Oxidation

​A substance has been oxidised when it:

• gains oxygen;

• loses hydrogen;

• loses electrons;

• increases its oxidation state after a reaction.

Revision on Reduction

Reduction is the reverse of oxidation.
A substance is reduced when it:

• loses oxygen;

• gains hydrogen;

• gains electrons;

• decreases its oxidation state after a reaction.

Oxidation and Reduction in Terms of Changes in Oxidation State

​What is an Oxidation State?

Oxidation state is the charge an atom of an element would have if it existed as an ion in a compound.

This is true even if the atom is covalently bonded.
When a substance loses or gains electrons, its oxidation state changes.

Determining Oxidation State: Rule 1

1. The oxidation state of a free element is zero

E.g: S, Na, O_2, N_2,
Before we talk about oxidation in terms of an increase in oxidation number, we need to understand how we determine and assign oxidation states to an atom, or ion of an element.

In this rule, it simply means that the oxidation state of an atom of an element, not combined with another element, is zero.

Determining Oxidation State: Rule 2

​2.The oxidation state of a simple ion is the same as the charge on the ion.

E.g
Na⁺ = +1
Mg²⁺ = +2
Cl^- = -1
S^2- = -2

Determining Oxidation State: Rule 3

​3.   Some elements have a fixed oxidation state in their compounds.

• Group I elements (e.g. Na, K) have an oxidation state of +1 in compounds.
• Group II elements (e.g. Mg, Ca) have an oxidation state of +2 in compounds.
• Hydrogen usually has an oxidation state of +1 in most compounds
• Oxygen usually has an oxidation state of -2 in most compounds

Determining Oxidation State: Rule 4

​4.The oxidation states of all the atoms or ions in a compound add up to zero.     

E.g. MgCl₂
Find the O.S of the element chlorine.
Let the O.S of chlorine be x.
The O.S of Mg²⁺ ion is fixed at +2.
The overall O.S adds up to 0 as MgCl₂ is a compound.
+2 + 2(x) = 0
2x = -2
x = -1
Therefore the O.S of Chlorine is -1.

Determining Oxidation State: Rule 5

​5. The sum of oxidation numbers of all the atoms in a polyatomic ion is the same as the charge on the ion.

What is the oxidation state of S in SO₄²⁻?
Let the unknown be x.
The sum of the O.S in this ion is -2 as the overall charge in this ion is -2.
x + 4( -2) = -2
x = +8-2
x= +6

Multiple Choice

The oxidation of sodium ion, Na⁺ is __.

• +1

• 0

• -1

• -2

Multiple Choice

What is the oxidation state of nitrogen in NO₂ ?

• -2

• +2

• -4

• +4

Multiple Choice

The oxidation state of Manganese in KMnO₄ is __.

• +6

• +7

• -1

• -2

Multiple Choice

The oxidation state of sulfur in SO₃ is __.

• -2

• +2

• +4

• +6

Multiple Choice

The oxidation state of sulfur in SO₃^2- is __.

• -2

• +2

• +4

• +6

GOOD JOB!!!