topic 01 - oxidation, reduction and redox equations

• what is a redox reaction?


  one where electrons are transferred between species.
• what happens in the process of reduction?


  electrons are gained.
• what happens in the process of oxidation?


  electrons are lost.
• what is the acronym for redox reactions?

  Oxidation

  Is

  Loss

  Reduction

  Is

  Gain
• what happens during redox reaction?


  one species is oxidised and loses electrons. These electrons are then transferred to another species which is reduced as it gains electrons.
• what is the oxidising agent?


  the species which accepts the electrons and is reduced.
• what is the reducing agent?


  the species which donates the electrons and is oxidised.
• what is the oxidation state/number?


  a measure of the number of electrons which have been gained or lost by the element.
• what is the oxidation rule regarding uncombined elements?


  the oxidation state of an element in its uncombined state is 0. eg: Na, Al, = 0.
• what is the oxidation rule regarding the oxidation state of oxygen in a compound?


  the oxidation state of oxygen in a compound is -2 except when its found in a peroxide.
• what is the oxidation rule regarding a neutral molecule?


  for a neutral molecule the sum of oxidation states of the combined elements must be 0.
• what is the oxidation rule regarding hydrogen in a compound?


  the oxidation state of hydrogen in a compound is +1 except when its found in a metal hybrid.
• what is the oxidation rule regarding the oxidation state of an ion?


  the oxidation state of an ion of an element is equal to the charge on the ion.
• what is the oxidation rule regarding compound ions?


  for a compound ion the sum of the oxidation states for all the combined elements must be equal to the charge on the ion.
• what can changes that occur in the oxidation state of an element be used for?


  they can be used to identify which species is being oxidised and which is being reduced.
• how can we look at the oxidation state and work out if an element has been reduced?


  if the oxidation state of the element becomes more negative then it has gained electrons and so been reduced.
• what can half equations be used to show?


  to show the oxidation and reduction processes taking place in redox reactions.
• how does a half equation show oxidation?


  if a half equation shows an oxidation process the electrons will be shown as products.
• how does a half equation show reduction?


  if a half equation shows a reduction process the electrons will be shown as reactants.
• what are the steps to writing half equations?


  1. write down the chemical formulae for reactants and products.
  2. balance the atoms undergoing the process (not hydrogen or oxygen.)
  3. balance the oxygen atoms by adding one or more water molecules to the opposite side of the equation.
  4. balance the hydrogen atoms by adding one or more H+ ions on the opposite side of the equation.
  5. balance the negative charges on both sides of the half equation by adding electrons on to the same side as the H+ ions or the opposite side to any negative charge.
  6. complete a check that everything is balanced.
• in a redox reaction, why is the number of electrons being gained and lost always equal?


  because the atoms can't gain more electrons than are released.,