Oxidation & Reduction

Transition elements can bond in different ways by forming ions with different charges
When naming, the charge on the ion is shown by using a Roman numeral after the element's name
For example, iron can form different ions
- Iron ions with a 2+ charge, Fe²⁺, are called iron(II) ions
- Iron ions with a 3+ charge, Fe³⁺, are called iron(III) ions
The Roman numeral is the oxidation number of the element
For example, iron reacts with oxygen to form iron oxide
- But the name and formula of the product depend on the oxidation state of the iron ions
- Iron(II) ions
  - The iron oxide product contains iron(II) ions, Fe²⁺
  - The name of this product is iron(II) oxide
  - The formula of this product is FeO
- Iron(III) ions
  - The iron oxide product contains iron(III) ions, Fe³⁺
  - The name of this product is iron(III) oxide
  - The formula of this product is Fe₂O₃

State the oxidation number of the transition metal ion in silver(I) chloride, AgCl.
Name, including Roman numeral, the compound with the formula CoCl₂.

Answers:

The oxidation number of the transition metal ion in silver(I) chloride, AgCl, is 1
- Remember: The Roman numeral gives the oxidation number of the element before
The name, including Roman numeral, of the chemical with the formula CoCl₂ is cobalt(II) chloride
- CoCl₂ contains two chloride ions, each with a 1- charge
- So, the cobalt ion has a 2+ charge
- This means the compound contains cobalt(II) ions, Co²⁺
- Therefore, it is called cobalt(II) chloride

A redox reaction is where oxidation and reduction take place together at the same time in the same reaction
In terms of oxygen:
- Oxidation is where oxygen is added to an element or a compound
- Reduction is where oxygen is removed from an element or compound
The reaction between zinc oxide and carbon is an example of a redox reaction
- Zinc oxide is reduced because it has lost oxygen
- Carbon is oxidised because it has gained oxygen

oxidation-and-reduction---oxygen Both reduction and oxidation has occurred in this reaction so it is classed as a redox reaction

Explain which chemicals that are reduced and oxidised in the reaction between iron(III) oxide and carbon.

iron(III) oxide + carbon monoxide → iron + carbon dioxide

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Answer:

BWChinGG_reduction-of-ironiii-oxide

You may see the term oxidation state used instead of oxidation number.

Although there is a subtle difference between the two terms (this is beyond the scope of this course), they are often used interchangeably.

Usually oxidation number is used to refer to the Roman numerals found within the name.

Oxidation & Reduction (CIE IGCSE Chemistry)