Shapes of titration curves

1
Titration Curves for Redox Systems

• Shapes of titration curves
• Compare shapes of titration curves for the
  titration of 0.0500 M Fe2 with
• 0.1000 M Ce4
• 0.0200 M MnO4-
• 0.01667 M Cr2O72-
• Effect of concentration
• Since up to equivalence point, E depends on ratio
  of mol Fe2/Fe3, E vs. vol constant and
  independent of concentration of Fe
• ?t equivalence point
• For Fe2/Ce4
• For Fe2/MnO4-
• For Fe2/Cr2O72-

Up to Ce4 equivalence point, curves all same The
Nernst Equation for the Fe3/Fe2 couple used to
calculate the curve Beyond each equivalence
point, use oxidizing agent couple
2
Titration Curves for Redox Systems
Effect of potential difference on titration
curve E0 analyte 0.2000 V A, E0 titrant 1.200
V B, E0 titrant 1.000 V C, E0 titrant 0.800
V D, E0 titrant 0.600 V E, E0 titrant 0.400
V Both analyte and titrant undergo a 1
electron change
3
Titration Curves for Redox Systems
4
Titration Curves for Redox Systems

• Shapes of titration curves
• Effect of Concentration
• Beyond the equivalence point
• For Fe2/Ce4
• For Fe2/MnO4-
• For Fe2/Cr2O72-
• Indicators
• Specific indicators respond to particular
  reactants or products associated with the redox
  reaction
• Starch is specific for reactions involving I3-
• MnO4- is self indicating
• Oxidation - reduction indicators have different
  colors in their reduced and oxidized forms

5
Titration Curves for Redox Systems

• Indicators
• Oxidation - reduction indicators

• Example ferroin - 1,10-phenanthroline iron(II)