redox

• Reducing agents


  Electron donors
• Oxidising agents


  Electron acceptors
• Oxidation


  1. Process of electron loss

  2. Involves an increase in oxidation number
• Reduction


  1. Process of electron gain

  2. Involves a decrease in oxidation number
• Rules for assigning oxidation numbers

  • All uncombined elements have an oxidation number of zero
  • The oxidation numbers of the elements in a compound add up to zero
  • The oxidation number of a monoatomic ion is equal to the ionic charge
  • In a polyatomic ion, the sum of the individual oxidation numbers of the elements adds up to the charge on the ion
  • Several elements have invariable oxidation numbers in their common compounds
• Note the oxidation number of Cl in CaCl2 = -1 and not -2 because there are two Cl's
• Always work out the oxidation per one atom of the element
• Redox equations and half equations

  1. Br2 (aq) + 2I- (aq) → I2 (aq) + 2 Br- (aq)

  2. Br2 (aq) + 2e- → 2 Br- (aq)

  3. 2I- (aq) → I2 (aq) + 2 e-
• Oxidising agent


  Bromine water, electron acceptor
• Reducing agent


  Iodide ion, electron donor
• Oxidising agent


  Species that causes another element to oxidise, itself reduced in the reaction
• Reducing agent


  Species that causes another element to reduce, itself oxidised in the reaction
• Reduction half equation


  Shows the parts of a chemical equation involved in reduction, with electrons on the left
• Oxidation half equation


  Shows the parts of a chemical equation involved in oxidation, with electrons on the right
• Balancing redox equations


  1. Work out oxidation numbers for element being oxidised/reduced

  2. Add electrons equal to the change in oxidation number

  3. Check that the sum of the charges on the reactant side equals the sum of the charges on the product side
• Writing half equations for complex substances

  1. Balance the change in oxidation number with electrons

  2. Add H2O in products to balance O's

  3. Add H+ in reactants to balance H's in H2O

  4. Check that the sum of the charges on the reactant side equals the sum of the charges on the product side
• Combining half-equations


  1. Reduction half equation and oxidation half equation must have equal numbers of electrons

  2. Multiply half equations to get equal electrons

  3. Add half equations together and cancel electrons