Oxidation, reduction and redox reactions

• Redox reactions involve a transfer of electrons from the reducing agent to the oxidising agent.
• The change in the oxidation state of an element in a compound or ion is used to identify the element that has been oxidised or reduced in a given reaction.
• Oxidation is the process of electron loss and oxidising agents are electron acceptors.
• Reduction is the process of electron gain and reducing agents are electron donors.
• Oxidation involves an increase in oxidation state.
• Reduction involves a decrease in oxidation state.
• How to work out the oxidation state of an element in a compound or ion from the formula: Rules

  • The oxidation state of an uncombined element is zero.
  • The sum of the oxidation states of all the atoms or ions in a neutral compound is zero.
  • The sum of the oxidation states of all the atoms in an ion is equal to the charge on the ion.

  = Basically, the oxidation state is how many other ions it can create.
• Any redox reaction is made up of two half-reactions: in one of them electrons are being lost (an oxidation process) and in the other one those electrons are being gained (a reduction process).
• How to write half-equations identifying the oxidation and reduction processes in redox reactions:

  1.  Write element before oxidation or reduction reaction. If it is an oxidation reaction, it will lose electrons, for reduction it will gain.
  2. Write the electrons being lost or gained.
  3. REMEMBER to BALANCE THE EQUATION.

  When combining half-equations to create an ionic equation, ignore the electrons, only include the elements. The electrons being lost have to match those being gained, therefore you might have to multiply a half-equation.