redox equations

• What do ionic half-equations show?

  Electron transfer
• What do half-equations illustrate in redox reactions?

  The electrons lost or gained
• What is the half-equation for the oxidation of sodium?

  Na ➔ Na+ + e-
• How can you form a complete redox equation?

  By combining oxidation and reduction half-equations
• What are the steps to write a redox equation for magnesium and oxygen producing magnesium oxide?

  1. Write oxygen reduction half-equation: O2 + 4e- ➔ 2O2-
  2. Write magnesium oxidation half-equation: Mg ➔ Mg2+ + 2e-
  3. Double magnesium half-equation: 2Mg ➔ 2Mg2+ + 4e-
  4. Combine half-equations: O2 + 4e- + 2Mg ➔ 2MgO + 4e-
  5. Cancel equal electrons: O2 + 2Mg ➔ 2MgO
• What are the steps to write a redox equation for aluminium and chlorine producing aluminium chloride?

  1. Write aluminium oxidation half-equation: Al ➔ Al3+ + 3e-
  2. Write chlorine reduction half-equation: Cl2 + 2e- ➔ 2Cl-
  3. Adjust half-equations: 2Al ➔ 2Al3+ + 6e- and 3Cl2 + 6e- ➔ 6Cl-
  4. Combine half-equations: 2Al + 3Cl2 + 6e- ➔ 2AlCl3 + 6e-
  5. Cancel equal electrons: 2Al + 3Cl2 ➔ 2AlCl3
• What are the steps to write a redox equation for the reduction of manganate(VII) ions by Fe2+ ions?

  1. Write iron oxidation half-equation: Fe2+(aq) ➔ Fe3+(aq) + e-
  2. Write manganate reduction half-equation: MnO4-(aq) + 8H+(aq) + 5e- ➔ Mn2+(aq) + 4H2O(l)
  3. Adjust iron half-equation: 5Fe2+(aq) ➔ 5Fe3+(aq) + 5e-
  4. Combine half-equations: MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) ➔ Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)
  5. Cancel equal electrons: MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) ➔ Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)
• How can you confirm the correctness of the number of electrons in a redox equation?

  By checking changes in oxidation numbers
• What is disproportionation in redox reactions?

  Simultaneous oxidation and reduction of an element
• In the reaction Cl2 + 2OH− ➔ ClO− + Cl− + H2O, what happens to chlorine?

  It is both oxidised and reduced
• What is the oxidation number change of Cl in the disproportionation reaction?

  Increases from 0 to +1 and decreases to -1