Oxidation, Reduction and Redox Equations

Oxidation in terms of oxygen

Addition of oxygen

Reduction in terms of oxygen

Removal of oxygen

Oxidation in terms of hydrogen

Removal of hydrogen

Reduction in terms of hydrogen

Addition of hydrogen

Oxidation in terms of electrons

Loss of electrons

Reduction in terms of electrons

Gain of electrons

What is an oxidising agent?

Species that oxidises another species by removing one or more electrons. When it reacts, it gains electrons and is reduced.

What is a reducing agent?

Species that reduces another species by adding one or more electrons. When it reacts, it loses electrons and is therefore oxidised.

What is a disproportionation reaction?

Simultaneous oxidation and reduction of an element in a single reaction.

What is an oxidation number?

A number assigned to an atom in a compound that represents the number of electrons lost or gained by that atom

Oxidation number of an uncombined element

0

Sum of all oxidation numbers in a neutral compound

0

Sum of all oxidation numbers of an ion

Equal to the charge on the ion

Which element in a substance is given a negative oxidation number?

The more electronegative element

When is hydrogen’s oxidation number -1?

When it’s combined with a less electronegative element

When is oxygen’s oxidation number -1?

In peroxides (H₂O₂)

Hydrogen oxidation number

+1/-1

Oxygen oxidation number

-2/-1

Group 1 metals oxidation number

+1

Group 2 metals oxidation number

+2

Aluminium oxidation number

+3

Group 7 oxidation number

-1

When do the halogens (Cl,Br,I) have an oxidation number different to -1?

In compounds with oxygen and fluorine

Oxidation in terms of oxidation number

Oxidation number increases.

When an element is oxidised, what does the increase in oxidation number represent?

The number of electrons lost

Reduction in terms of oxidation number

Oxidation number decreases

When an element is reduced, what does the decrease in oxidation number represent?

The number of electrons gained.

In a redox reaction, what is the number of electrons lost equal to?

The number of electrons gained

In a redox reaction, what is the total increase in oxidation number equal to?

The total decrease in oxidation number

What does the roman numeral in the brackets of a systematic name symbolise?

The oxidation number of the element which can have more than one oxidation states.

Using oxidation numbers to balance equations

Oxidation numbers on both sides must be equal

Steps for constructing half equations

1. Balance redox element

2. Balance oxygen by adding water

3. Balance hydrogen by adding hydrogen ions

4. Balance charge using electrons