Using Conductivity to Find an Equivalence Point

Recommended for grades 9–12.

Figure from experiment 26 from Chemistry with Vernier

Introduction

In this experiment, you will monitor conductivity during the reaction between sulfuric acid, H₂SO₄, and barium hydroxide, Ba(OH)₂, in order to determine the equivalence point. From this information, you can find the concentration of the Ba(OH)₂ solution. You will also see the effect of ions, precipitates, and water on conductivity. The equation for the reaction in this experiment is:

${\text{B}}{{\text{a}}^{{\text{2 + }}}}{\text{(aq) + 2 O}}{{\text{H}}^{\text{ - }}}{\text{(aq) + 2 }}{{\text{H}}^{\text{ + }}}{\text{(aq) + S}}{{\text{O}}_{\text{4}}}^{{\text{2 - }}}{\text{(aq)}} \to {\text{BaS}}{{\text{O}}_{\text{4}}}{\text{(s) + }}{{\text{H}}_{\text{2}}}{\text{O(1)}}$

Before reacting, Ba(OH)₂ and H₂SO₄ are almost completely dissociated into their respective ions. Neither of the reaction products, however, is significantly dissociated. Barium sulfate is a precipitate and water is predominantly molecular.

As 0.02 M H₂SO₄ is slowly added to Ba(OH)₂ of unknown concentration, changes in the conductivity of the solution will be monitored using a Conductivity Probe. When the probe is placed in a solution that contains ions, and thus has the ability to conduct electricity, an electrical circuit is completed across the electrodes that are located on either side of the hole near the bottom of the probe body. This results in a conductivity value that can be read by the interface. The unit of conductivity used in this experiment is microsiemens per centimeter, or μS/cm.

Prior to doing the experiment, it is very important for you to hypothesize about the conductivity of the solution at various stages during the reaction. Would you expect the conductivity reading to be high or low, and increasing or decreasing, in each of these situations?

When the Conductivity Probe is placed in Ba(OH)₂, prior to the addition of H₂SO₄.
As H₂SO₄ is slowly added, producing BaSO₄ and H₂O.
When the moles of H₂SO₄ added equal the moles of BaSO₄ originally present.
As excess H₂SO₄ is added beyond the equivalence point.

Objectives

In this experiment, you will

Hypothesize about the conductivity of a solution of sulfuric acid and barium hydroxide at various stages during the reaction.
Use a Conductivity Probe to monitor conductivity during the reaction.
See the effect of ions, precipitates, and water on conductivity.

Sensors and Equipment

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

Conductivity Probe
Drop Counter (optional)

Additional Requirements

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

Download Experiment Preview

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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