Summary

In this demonstration, students will make predictions and then observe how conductivity is measured in several electrolyte and nonelectrolyte solutions. A short discussion about electrolytes, ions, ionic compounds, and galvanic cells will follow.

Grade Level

Middle School

NGSS Alignment

This demonstration will help prepare your students to meet the performance expectations in the following standards:

• Scientific and Engineering Practices:
  • Asking Questions and Defining Problems
  • Analyzing and Interpreting Data

Objectives

By the end of this demonstration, students should be able to

• Understand that the conductivity of solutions can be measured.
• Differentiate between electrolytes and nonelectrolytes.

Chemistry Topics

This demonstration supports students’ understanding of

• Solutions
• Conductivity
• Electrolytes
• Nonelectrolytes
• Ions
• Batteries

Time

Teacher Preparation: 20 minutes
Lesson: 60 minutes

Materials

• Deionized or distilled water
• Tap water (see Teachers Note below)
• Salt
• Sugar
• Cups or beaker for each solution
• Optional: vinegar, orange juice, sports drinks, lemon juice or other common liquids
• Conductivity probe (Flinn Conductivity Meter)
• Paper towels

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wear proper safety gear during chemistry demonstrations.
• The conductivity meter is very safe. It uses a 9-volt battery and being shocked is not possible.

Teacher Notes

• Teachers are encouraged to engage students by first showing the short video, How Batteries Work, (6 minutes) from Mystery Science. A student question sheet has been provided.
• Before preparing the solutions for the demonstration, teachers should test your tap water to see if it conducts. It probably will, but if not, you can use the tap water to prepare your solutions and skip the deionized or distilled water. (Note: distilled water may conduct slightly.)
• If time permits you can add additional samples, such as vinegar, baking soda solution, orange juice, sports drinks, or other common liquids to be tested. Expected results for some of these items have been included in the Answer Key.
• Use a conductivity probe to test each of the samples. The conductivity probe used in this demonstration was a Flinn Conductivity Meter. If you do not have one, there are several resource videos online that show how to make one.
• The conductivity meter scale below from Flinn Scientific should be used to interpret the data from the conductivity meter. It describes the light brightness and associated conductivity of the solution:

• Demonstration Procedures:
  • Prepare samples of deionized or distilled water, tap water, saltwater solution, and sugar solution.
    • For the salt and sugar solutions, precise measurements of solute are not necessary. Teachers can add approximately 1 tbsp. of each to a cup of deionized water. Make sure that each solute fully dissolves in the water.
  • Optional: If time permits you can add additional samples, such as vinegar, baking soda solution, orange juice, sports drinks, or other common liquids.
  • Use a conductivity probe to test each of the samples.
  • Carefully rinse the probe electrodes after testing each of the samples. Dry them with a clean paper towel before testing the next sample.
  • Start by testing the deionized or distilled water and the sugar solution. They should not conduct, and the red light won’t be lit or will be very dim. The green light will not be lit.
  • Test the tap water. Depending on the quality of your water the red light will likely be lit.
  • Test the salt solution and any of the other solutions you prepared. The salt solution will conduct and both the red and green lights will be lit.
  • Make a note of the relative brightness of the light for each sample.

• A data table has been provided for students to record the conductivity results.
• Students should complete the “Prediction” column first to indicate if they believe if each of the solutions are or are not conductive. During the demonstration students should record their observations in the appropriate column of the data table.
• After the demonstration, the teacher should lead a discussion prompted by the question that follows the data table, “Based on your observations, which of the tested solutions would be a good electrolyte for a battery?”
• A list of vocabulary words has been provided for students to explain following the discussion.
• An Answer Key document that includes expected results is available for teacher reference.