Redox Reaction

• Oxdation occurs when a substance gains oxygen
• Reduction occurs when a substance loses oxygen
• Lead oxide + carbon → lead + carbon monoxide

  • the lead oxide is reduced so it loses oxygen
  • the carbon is oxidized so it gains oxygen
• Oxidation occurs when a substance loses electrons
• Reduction occurs whena. substance gains electrons
• LEO the lion goes GER

  • L E O - loss off electrons is oxidation
  • G E R - gain of electrons is reduction
• Redox reactions - oxidation and reduction take place together at the same time in the same reaction
• Oxidation - a reaction in which oxygen is added to an element or a compound
• Reduction - a reaction in which oxygen is removed from an element or compound
• Transition elements can bond in different ways by forming ions with different charges
• • When naming, the charge on the ion is shown by using a Roman numeral after the element's name
  • e.g. iron can form ions with a 2+ charge, called iron(II) ions or a 3+ charge, called iron(III) ions
  • The Roman numeral is the oxidation number of the element
• When iron reacts with oxygen to form iron oxide, the formula depends on the oxidation state of the iron ions

  • The compound where iron has a 2+ charge has the formula FeO and is called iron(II) oxide
  • The compound where iron has a 3+ charge has the formula Fe2O3 and is called iron(III) oxide
• You may see the term oxidation state used instead of oxidation number

  • Although there is a subtle difference between the two terms (this is beyond the scope of this course), they are often used interchangeably
  • Usually oxidation number is used to refer to the Roman numerals found within the name.
• Electrons go on the most positive side
• Magnesium burns in oxygen to form magnesium oxide

  • magnesium is oxidized - lost 2 electrons to form Mg^2+ ion
  • oxygen is reduced - gains 2 electrons to form O^2- ion
• Oxidizing agent - substances that causes another to be oxidized
• Reducing agent - substance that causes another to be reduced
• Oxidation and reduction occur together in a reaction

  • These are often called REDOX reactions
• Rules of oxidising numbers

  1. Oxidation number of oxygen in a compound is -2
  2. Oxidation number of hydrogen in a compound is +1
  3. The sum of oxidation numbers in a compound or molecule is equal to zero
  4. Oxidation number of a monatomic ion is equal to the charge on the ion
  5. The sum of oxidation numbers of polyatomic ion is equal to the charge on the ion
  6. The oxidation number of an element is equal to the zero
• Oxidation numbers are written as roman numerals in compounds and show their oxidation state
• An increase in oxidation numbers mean that oxidation has occurred
• A decrease/reduction in oxidation numbers means that reduction has occurred
• Oxidation number is tne same as charge
• When reduction has occured to a compound/element, it shows that it is the oxidizing agent
• When oxidation has occured to a compound/element, it shows that it is a reducing agent
• How to know which substance is the reducing agent?

  The substance that loses electrons is the reducing agent
• What solution tests for reducing agents?

  aqueous potassium mangante (VII)