A titration, as you recall, is a convenient method of learning more about a solution by reacting it with a second solution of known molar concentration. There are a number of ways to measure the progress of a titration. The method used in this experiment is called a potentiometric titration, in which the electric potential of a reaction is monitored. All acid-base titrations that are measured by a pH probe are potentiometric; thus, this method is not as unusual as it may seem.

You will conduct an oxidation-reduction reaction in this experiment in order to determine the amount of iron (II) ions in a solid sample of ferrous ammonium sulfate hexahydrate, (NH4)2Fe(SO4)2•6H2O. The oxidizing agent for the sample will be ammonium cerium (IV) nitrate, (NH4)2Ce(NO3)6. The net ionic equation for the reaction is shown below.

{\text{C}}{{\text{e}}^{{\text{4}} + }}\left( {{\text{aq}}} \right) + {\text{ F}}{{\text{e}}^{{\text{2}} + }}\left( {{\text{aq}}} \right) \to {\text{C}}{{\text{e}}^{{\text{3}} + }}\left( {{\text{aq}}} \right) + {\text{ F}}{{\text{e}}^{{\text{3}} + }}\left( {{\text{aq}}} \right)

This experiment illustrates the electrical nature of chemical reactions, and offers practice with a process for observing and measuring an oxidation-reduction reaction.


In this experiment, you will

  • Conduct the potentiometric titration of the reaction between ferrous ammonium sulfate hexahydrate and ammonium cerium (IV) nitrate.
  • Measure the potential change of the reaction.
  • Determine the molar concentration of iron (II) ions in a sample of ferrous ammonium sulfate hexahydrate.