redox

• Oxidation


  The process of electron loss
• Reduction


  The process of electron gain
• 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
• Identifying oxidation numbers


  1. Use the rules to identify the oxidation numbers of elements that have variable oxidation numbers

  2. Always work out the oxidation for one atom of the element
• Naming using Roman Numerals

  In IUPAC convention, the various forms of sulfur, nitrogen and chlorine compounds where oxygen is combined are all called sulfates, nitrates and chlorates with relevant oxidation number given in roman numerals
• Redox Reactions


  • Metals generally form ions by losing electrons with an increase in oxidation number to form positive ions
  • Non-metals generally react by gaining electrons with a decrease in oxidation number to form negative ions
• Redox reactions


  • 4Li + O2 2Li2O
  • WO3 + 3H2 W + 3H2O
  • 2Sr(NO3)2 2SrO + 4NO2 + O2
• Oxidising and Reducing agents

  • Lithium is oxidising because its oxidation number is increasing from 0 to +1
  • Oxygen is reducing because its oxidation number is decreasing from 0 to -2
  • Hydrogen is oxidising because its oxidation number is increasing from 0 to +1
  • Tungsten is reducing because its oxidation number is decreasing from +6 to 0
  • Oxygen is oxidising because its oxidation number is increasing from -2 to 0
  • Nitrogen is reducing because its oxidation number is decreasing from +5 to+4
• Redox Reactions of Metals and acid

  1. 2HCl + Mg MgCl2 +H2

  2. Fe + H2SO4 FeSO4 +H2
• Observations


  • These reactions will effervesce because H2 gas is evolved and the metal will dissolve
  • Note that not all the oxygen atoms are changing oxidation number in this reaction
• Oxidising and Reducing agents

  • Nitrogen is oxidising because its oxidation number is increasing from -3 to -2
  • Chlorine is reducing because its oxidation number is decreasing from +1 to -1