Redox titrations

• Thiosulfate redox titration

  2S2O3 2- + I2 > 2I- + S4O6 2-
• problem of iodine colour change

  • iodine is a brown coloured solution
  • the colour fades gradually and it is difficult to detect when it happens
  • solution add starch indicator containing iodine, the solution will turn blue black
  • titration will be blue black to colourless
• Manganate redox titration

  MnO4 - + 8H+ + 5Fe 2+ > Mn2+ + 4H2o + 5Fe 3+
• Colour change for manganate redox titration

  purple to colourless