3.1.7 Oxidation, reduction and redox equations

• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• Oxidising agents are electron acceptors, so they gain electrons from the substance that is being oxidised and are reduced.
• Reducing agents are electron donors, so they donate electrons to the molecule to reduce it and are oxidised themselves.
• The oxidation number of uncombined elements are always 0 e.g. Fe, Cl2, O2.
• The oxidation number of ions is the same as the charge on the ion.
• The oxidation number of hydrogen is +1, except in hydrides (HF) where it is -1.
• The oxidation number of oxygen is -2, except in peroxides (H2O2) where it is -1 and +2 in OF2.
• Reduction is a decrease in oxidation number.
• Oxidation is an increase in oxidation number.
• Balancing and combining half equations steps

  1. deduce the half equation for both the reduction and oxidation reaction
  2. balance any atoms except for oxygen and hydrogen
  3. balance any oxygens with water (H2O)
  4. balance any hydrogens with H+
  5. balance charges with electrons (e-)
  6. balance electrons
  7. cancel out like terms and combine half equations