Edexcel A Level Chemistry:复习笔记2.1.2 Types of Reduction & Oxidation

• Oxidation and reduction in a reaction can be demonstrated in terms of electron transfer
  • For example:

2NH3 + 3Br2 → N2 + 6HBr

• The oxidation number of N in NH3 has changed from -3 to 0
  • As the oxidation number has increased, nitrogen has been oxidised
• The oxidation number of Br has changed from 0 to -1
  • As the oxidation number has decreased, bromine has been reduced
• Overall, nitrogen has reduced bromine by donating electrons

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

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

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

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)