Students are often a little shocked to learn that water is actually a poor conductor of electricity. So, why the caution with electronics near water? This is because water can dissolve ionic compounds into individual ions that carry electric charges—electrolytes. Measuring a solution’s conductivity tells us about its ionic content and its electrical conductivity, and investigating this phenomena can help students develop a stronger understanding of the structure and properties of matter and chemical reactions. The Go Direct^® Conductivity Probe, with its wide range of 0 to 20,000 μS/cm and alternating current that improves sensor longevity, is an excellent tool for deepening student understanding of many fundamental chemistry concepts, from ionic bonding to chemical titrations. Here are three investigations to help you get started.

Investigation 1: Electrolytes and Ionization

Properties of Solutions: Electrolytes and Non-Electrolytes
Experiment #13, Chemistry with Vernier

Many students, especially athletes, may recognize the word “electrolytes,” but they may not understand their chemical significance. Electrolytes are salts and molecules that ionize to some degree, and by investigating them, students can develop a stronger understanding of ionic compounds, how ionic compounds dissociate in water, and the role ions play in conducting electricity.

In this experiment, students explore the properties of strong, weak, and non-electrolytes by observing a range of substances in aqueous solutions using the Go Direct Conductivity Probe. When ions are present in a solution, they complete an electrical circuit across the probe’s electrodes, generating a conductivity reading in microsiemens per centimeter (μS/cm) that students can use to classify the different substances.

For an introductory lesson, this experiment can be tailored to focus on ionic and molecular compounds. For a more advanced version, students can investigate molecular acids as well.

The conductivity values of three different solutions (CaCl₂, AlCl₃, and NaCl) are collected and displayed in Vernier Graphical Analysis^® Pro. Note: Bar graphs and categorical data are Pro features.

As students test the conductivity of each solution using the probe, real-time data is graphed and displayed in Vernier Graphical Analysis. The recorded conductivity values reflect the solution’s ion concentration: strong electrolytes show high conductivity, weak electrolytes show low conductivity, and nonelectrolytes show none. After collecting data from each solution, students can make inferences about whether they contain ionic or molecular compounds and classify them as strong or weak electrolytes.

This experiment not only helps students observe these distinctions but also understand the different factors affecting a solution’s conductivity.

TECH TIP

When a sensor is connected, Graphical Analysis defaults to “Time Based” data-collection mode. Changing to “Event Based” mode can be more useful in experiments where time-based data isn’t relevant. In this mode, you can choose between “Events with Entry,” which prompts you to manually enter each event value and “Selected Events,” which automatically ascribes the row number as the event value.

In the basic version of Graphical Analysis, “Selected Events” is the most efficient mode for this experiment; just make sure your students track sample numbers to their corresponding compounds. If you have Graphical Analysis Pro, choose “Events with Entry” mode and enter the name of the compound directly in the table.

Investigation 2: Concentration and Molarity

Conductivity of Solutions: The Effect of Concentration
Experiment #14, Chemistry with Vernier

After students have a better understanding of how different compounds affect the conductivity of a solution, it’s an easy transition to explore how the concentration of ions in a solution also influences its ability to conduct electricity. This investigation helps introduce students to the concept of molarity and the relationship between solute concentration and solution properties.

In this experiment, students study the effect of increasing the concentration of an ionic compound on conductivity. Start by taking a look at one specific compound, such as sodium chloride (NaCl). When it dissolves in water, it releases ions according to the following equation:

NaCl(s) → Na⁺(aq) + Cl^–(aq)

Using the conductivity probe, students measure conductivity as they gradually add drops of concentrated NaCl to increase the concentration of the solution.

Conductivity data of sodium chloride, NaCl, collected and graphed as a function of concentration versus volume (in drops) in Graphical Analysis

The same procedure is used to investigate the effect of adding solutions with the same concentration (1.0 M) but different numbers of ions in their formulas: aluminum chloride, AlCl₃, and calcium chloride, CaCl₂.

Conductivity data of three ionic compounds (NaCl, AlCl₃, and CaCl₂) collected and graphed as a function of concentration versus volume (in drops) in Graphical Analysis

Ask your students to analyze the graph curves and describe how conductivity changes as the solution concentration increases. Why are their slopes different? This investigation is an easy, hands-on way to introduce students to the significance of molar concentration and its relationship to conductivity.

TECH TIP

If you have the Pro version of Graphical Analysis, you have access to a whole library of sample experiments, including this one! All Graphical Analysis sample experiments, which can be sorted by subject or lab book, include videos demonstrating the experiments along with the corresponding data. This is a great way to get started on topics that you may not have the equipment or opportunity to try in your lab, or for helping students catch up on missed work.

Investigation 3: Chemical Reactions and Changes

Using Conductivity to Find an Equivalence Point
Experiment #26, Chemistry with Vernier

By measuring conductivity before and after a chemical reaction, students can observe how reactions alter the ionic composition of a solution. This illustrates the concepts of reactants, products, and the conservation of matter in chemical reactions, as well as the effect of ions, precipitates, and water on conductivity.

In this experiment, students monitor conductivity during the reaction between sulfuric acid,
H₂SO₄, and barium hydroxide, Ba(OH)₂, in order to determine the equivalence point. Using their findings, they can then calculate the concentration of the Ba(OH)₂ solution. Adding an indicator before titration helps students visually identify the equivalence point when conductivity reaches its minimum value.

Students analyze the graph to identify when the conductivity reaches a minimum value—the equivalence point of the reaction.

Before starting the experiment, prompt your students to predict what will happen to the conductivity of the solution at various stages during the reaction. Do they expect the conductivity reading to be high or low, and increasing or decreasing, in each of the following situations?

• In Ba(OH)₂, before adding H₂SO₄
• When H₂SO₄ is slowly added, producing Ba(OH)₂ and H₂O
• When the moles of H₂SO₄ added equal the moles of BaSO₄ originally present
• When excess H₂SO₄ is added beyond the equivalence point

After completing the titration, discuss with your students how their data compare to their predictions and have them explain the reasoning behind any discrepancies.

TECH TIP

This experiment can be conducted using either a buret or a drop counter to perform the titration. With a buret, volumes must be read and entered in Graphical Analysis manually. With a Go Direct Drop Counter, volume data is recorded automatically in Graphical Analysis.

For best results, we recommend calibrating the drop counter prior to use. Note that this calibration is not stored to the sensor, as it varies depending on the reagent reservoir used. However, to save time in future experiments, record the calibrated drop size of your reagent reservoir. Then, when you use the reagent reservoir again, students can simply enter the drops/mL value in the calibration dialog, avoiding the need for recalibration.

These three investigations using the Go Direct Conductivity Probe provide engaging, hands-on learning experiences for students, helping them understand key concepts in ionic bonding and conductivity. For more tips and demonstrations, check out our webinar on teaching ionic and covalent bonds with conductivity.

We’re here to help! Reach out to us at chemistry@vernier.com or call 888-837-6437 with any questions. Looking for water quality investigations for your Go Direct Conductivity Probe? Check out our lab book Earth Science with Vernier or explore our other environmental science solutions.