Redox reactions and oxidation states

What are the three definitions for reduction?

• Loss of oxygen

• Gain of electrons

• Gain of hydrogen

What are the three definitions for oxidation?

• Gain of oxygen

• Loss of electrons

• Loss of hydrogen

Acronym for remembering the electron definitions of oxidation and reduction

OiL RiG

What is it called when reduction and oxidation happens simultaneously?

A redox reaction

What is an oxidising agent?

An agent that accepts electrons and gets reduced

What is a reducing agent?

An agent that donates electrons and gets oxidised

What does the oxidation state of an element tell you?

The total number of electrons it has donated or accepted in order to become neutral

What are oxidation states also called?

Oxidation numbers

What are the oxidation states of uncombined elements, such as Na or Fe?

Oxidation state = 0 because they are already neutral

What are the oxidation states of elements that are diatomic molecules, such as N₂ or Cl₂?

Oxidation state = 0

What would be the oxidation state of a monatomic ion (made up of 1 ion)?

Oxidation state would be the same as the charge of the ion

What would be the oxidation state of K⁺ and why?

Oxidation state = +1 because the ion would need to gain 1 electron to become neutral

What would be the oxidation state of Al³⁺?

Oxidation state = +3

What would be the oxidation state of Cl⁻?

Oxidation state = -1

What is the common oxidation state of oxygen and what are the variations?

Oxidation state = -2 → in Group 6 which forms O²⁻ ion so it needs to lose 2 electrons to become neutral, O.

• If it’s in hydrogen peroxide, H₂O₂, oxidation state = -1

• If it’s in a compound with fluorine, the oxidation state = +2

What are the oxidation agents of the transition elements (d-block) known for?

Their varying oxidation states

What would be the oxidation state for iron in iron (II) oxide?

Oxidation state = +2 → formula: FeO

What would be the oxidation state for iron in iron (III) oxide?

Oxidation state = +3 → formula: Fe₂O₃

What does the sum of the oxidation states in a neutral compound equal to?

The overall charge - 0

How would you work out the oxidation state of C in CO₂?

Overall charge = 0

The oxidation state of O = -2

2 oxygens in O₂, so 2 lots of -2

C + (-2) + (-2) = 0

Oxidation state of C = +4

What is the oxidation state of N in NH₃?

Overall charge = 0

Oxidation state of H = +1

N + 1 + 1 + 1 = 0

Oxidation state of N = -3

What is the oxidation state of O in H₂O₂?

Overall charge = 0

Oxidation state of H = +1

O + O + 1 + 1 = 0

O + O = -2

Oxidation state of O = -1

What is the oxidation state of O in F₂O?

Overall charge = 0

Oxidation state of F = -1

(-1) + (-1) + O = 0

Oxidation state of O = +2

What does the sum of the oxidation states in an ionic compound equal to?

The overall charge of the compound

What is the oxidation state of N in NH₄⁺?

Overall charge = +1

Oxidising state of H = +1

N + 1 + 1 + 1 + 1 = 1

Oxidising state of N = -3

What is the oxidation state of S in SO₄²⁻?

Overall charge = -2

Oxidation state of O = -2

S + (-2) + (-2) + (-2) + (-2) = -2

Oxidising state of S = +6