Vernier Software & Technology

# Using Conductivity to Find an Equivalence Point

## 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 features the following Vernier sensors and equipment.

### Option 2

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

## Chemistry with Vernier

See other experiments from the lab book.

 1 Endothermic and Exothermic Reactions 2 Freezing and Melting of Water 3 Another Look at Freezing Temperature 4 Heat of Fusion of Ice 5 Find the Relationship: An Exercise in Graphing Analysis 6 Boyle's Law: Pressure-Volume Relationship in Gases 7 Pressure-Temperature Relationship in Gases 8 Fractional Distillation 9 Evaporation and Intermolecular Attractions 10 Vapor Pressure of Liquids 11 Determining the Concentration of a Solution: Beer's Law 12 Effect of Temperature on Solubility of a Salt 13 Properties of Solutions: Electrolytes and Non-Electrolytes 14 Conductivity of Solutions: The Effect of Concentration 15 Using Freezing Point Depression to Find Molecular Weight 16 Energy Content of Foods 17 Energy Content of Fuels 18 Additivity of Heats of Reaction: Hess's Law 19 Heat of Combustion: Magnesium 20 Chemical Equilibrium: Finding a Constant, Kc 21 Household Acids and Bases 22 Acid Rain 23 Titration Curves of Strong and Weak Acids and Bases 24 Acid-Base Titration 25 Titration of a Diprotic Acid: Identifying an Unknown 26 Using Conductivity to Find an Equivalence Point 27 Acid Dissociation Constant, Ka 28 Establishing a Table of Reduction Potentials: Micro-Voltaic Cells 29 Lead Storage Batteries 30 Rate Law Determination of the Crystal Violet Reaction 31 Time-Release Vitamin C Tablets 32 The Buffer in Lemonade 33 Determining the Free Chlorine Content of Swimming Pool Water 34 Determining the Quantity of Iron in a Vitamin Tablet 35 Determining the Phosphoric Acid Content in Soft Drinks 36 Microscale Acid-Base Titration

### Experiment 26 from Chemistry with Vernier Lab Book

#### Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.