Redox Reactions

• Redox titrations


  Redox reactions used in titrimetric analysis to analyse reactions both theoretically and when carried out in practice
• Half equations


  Used to show the separate oxidation and reduction reactions that occur in a redox reaction

  
• Steps to construct half equations

  1. Balance all species excluding oxygen and hydrogen

  2. Balance oxygen using H2O

  3. Balance hydrogen using H+ ions

  4. Balance charges using e- (electrons)
• Potassium dichromate(VI)


  An oxidising agent used commonly in the oxidation of alcohols
• Potassium manganate(VII)


  An oxidising agent, MnO4- is reduced to Mn^2+

  
• Thiosulfate


  A reducing agent, S2O3^2- is oxidised to S4O6^2-

  
• Combining half equations


  1. The number of electrons must be the same for both half equations

  2. The molar ratio is crucial for redox titration calculations

  
• Redox titrations


  Carried out using a similar method to acid-base titration to accurately determine the concentration of an unknown substance by measuring it against a standardised titrant
• A common example is the reaction between a standard solution of potassium permanganate (KMnO4) and a solution containing an unknown concentration of Fe^2+ ions

  
• When at the neutralisation point, the solution of KMnO4 will turn from bright purple to almost colourless meaning there is a very clear endpoint to the titration
• Concordant results


  Titre values are said to be concordant if they are within 0.20 cm3 of each other