• There are three definitions of?oxidation?and?reduction? used in different branches of chemistry
• Oxidation?and?reduction?can be used to describe any of the following processes

Definitions and Examples of Oxidation & Reduction

Use the acronym "Oil Rig" to help you remember the definitions of oxidation and reduction

Oxidation States

• The?oxidation state?of an atom is the charge that would exist on an individual atom if the bonding were completely ionic
• It is like the electronic ‘status’ of an element
• Oxidation states?are used to
  • Tell if oxidation or reduction has taken place
  • Work out what has been oxidised and/or reduced
  • Construct half equations and balance redox equations

   

Oxidation States of Simple Ions

Answers:

a) 0? ? ?b) +3? ? c) +2? ? d) -2? ? e) 0? ? f) +3

• So, in simple ions, the oxidation stateof the atom is the charge on the ion:
  • Na+, K+, H+?all have an oxidation state of +1
  • Mg2+, Ca2+, Pb2+?all have an oxidation state of +2
  • Cl–, Br–, I–?all have an oxidation state of -1
  • O2-, S2-?all have an oxidation state of -2

   

Oxidising agent

• An oxidising agent?is a substance that?oxidises?another atom or ion by causing it to lose electrons
• An oxidising agent itself gets?reduced – it gains electrons
• Therefore, the?oxidation state?of the oxidising agent?decreases

Example of an oxidising agent in a chemical reaction

Reducing agent

• A reducing agent?is a substance that?reduces?another atom or ion by causing it to gain electrons
• A reducing agent itself gets?oxidised – it loses/donates electrons
• Therefore, the?oxidation?state?of the reducing agent?increases

Example of a reducing agent in a chemical reaction

• For a reaction to be a redox reaction, there must be both an oxidising and reducing agent present
• Some substances can act both as oxidising and reducing agents - look at the two roles of H2O2?in the previous examples
• The role they take is dependent on what they are reacting with and the reaction conditions

Answer

The correct option is?2

• • Oxidising agents are substances that oxidise other species, gain electrons and are themselves reduced.
  • Write down the oxidation numbers of each species in the reaction

   

• • In equation 2, Fe2+?oxidises Mg(0) to Mg2+(+2) and is itself reduced from Fe2+(+2) to Fe(0)

   

Roman numerals

• Roman numerals are used to show the oxidation states of?transition metals?which can have more than one oxidation state
• Iron can be both +2 and +3 so Roman numerals are used to distinguish between them
  • Fe2+?in FeO is written as?iron(II) oxide
  • Fe3+?in Fe2O3?is written as?iron(III) oxide

   

Answer

Answer 1:?Iron(II) chloride: the oxidation state of 2 Cl atoms is -2 and FeCl2?has no overall charge so the oxidation state of Fe is +2

Answer 2:?Chloric(VII) acid: the oxidation state of H is +1, 4 O atoms is -8 and HClO4?has no overall charge so the oxidation state of Cl is +7

Answer 3:?Nitrogen(IV) oxide: the oxidation state of 2 O atoms is -4 and NO2?has no overall charge so the oxidation state of N is +4

Answer 4:?Magnesium nitrate: this is a salt of the common acid, so it is named without including the oxidation state of the non-metal

Answer 5:?Potassium sulfate: this is a salt of the common acid, so it is named without including the oxidation state of the non-metal