An Oxidation-Reduction Titration: The Reaction of Fe2+ and Ce4+

Recommended for grades 9–12.

Figure from experiment 8 from Advanced Chemistry with Vernier

Introduction

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.

Objectives

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.

Sensors and Equipment

This experiment requires each of the following Vernier sensors and equipment (unless otherwise noted):

ORP Sensor
Drop Counter (optional)

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

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The student-version preview includes:

Step-by-step instructions for computer-based data collection
List of materials and equipment

Note: The experiment preview of the computer edition does not include essential teacher information, safety tips, or sample data. Instructions for Logger Pro and other software (such as LabQuest App or TI handheld software, where available) are on the CD that accompanies the book. We strongly recommend that you purchase the book before performing experiments.

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Standards Correlations

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