CIE A Level Chemistry复习笔记1.6.3 Oxidising & Reducing Agents

Oxidising & Reducing Agents

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 – gains electrons
  • Therefore, the ox. no. of the oxidising agent decreases

1.6-Electrochemistry-Example-Oxidising-Agent

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 – loses/donates electrons
  • Therefore, the ox. no. of the reducing agent increases

1.6-Electrochemistry-Example-Reducing-Agent

Example of a reducing agent in a chemical reaction

  • For a reaction to be recognised as a redox reaction, there must be both an oxidising and reducing agent
  • Some substances can act both as oxidising and reducing agents
  • Their nature is dependent upon what they are reacting with and the reaction conditions

Worked Example: Oxidising & reducing agents

1.6-Electrochemistry-Worked-example-Oxidising-and-reducing-agents

Answer

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

Oxidising-Reducing-Agents-Worked-Example-equation

In equation B, 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 number
  • Iron can be both +2 and +3 so Roman numerals are used to distinguish between them
    • Fe2+ in FeO can be written as Iron(II) oxide
    • Fe3+ in Fe2O3 can be written as Iron(III) oxide

Worked example: Systematic names of compounds

1.6-Electrochemistry-Worked-example-Systematic-names-of-compounds

Answer

Answer 1: Iron(II) chloride: ox. no. of 2 Cl atoms is -2 and FeCl2 has overall no charge so ox. no. of Fe is +2

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

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

Answer 4: Magnesium nitrate: this is a salt of the common acid, so they are named without including the ox. no. of the non-metal

Answer 5: Potassium sulfate: this is a salt of the common acid, so they are named without including the ox. no. of the non-metal

 

 

 

 

 

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