Summary

In this lab, students will analyze the conductivity of several common household solutions using a light emitting conductivity diode tester to determine if the solution is a strong or weak electrolyte. Students will interpret the brightness of the lightbulb to determine the strength of the electrolyte. Students will also have an opportunity to consider the connection between conductivity and bond type during this lab.

Grade Level

High school

AP Chemistry Curriculum Framework

This lab supports the following unit, topic and learning objective:

• Unit 3: Intermolecular Forces and Properties
  • Topic 3.2: Properties of Solids
    • SAP-5.B: Explain the relationship among the macroscopic properties of a substance, the particulate-level structure of the substance, and the interactions between these particles.

Objectives

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

• Use a conductivity tester in a solution to analyze its electrolyte strength.
• Distinguish between a strong and weak electrolyte.
• Understand the correlation between ion concentration of a solution and ability to conduct electricity.

Chemistry Topics

This lab supports students’ understanding of

• Solutions
• Conductivity
• Electrolytes

Time

Teacher Preparation: 15-20 minutes

Lesson: 40 minutes

Materials

(Per lab group)

• Four Test Solutions (examples: water, salt water, sugar water, baking soda water, vinegar)
• Wash bottle or beaker of distilled water
• Wash bottle or beaker of tap water
• Light Emitting Conductivity Diode Tester (see teacher notes)
• Paper towels

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• I use water solutions to test for electrical conductivity. They can test solutions of household items such as salt, sugar, vinegar or baking soda.
• A low cost conductivity tester can be made using a light emitting diode from Radio Shack (2 for less than $4), copper wire, a 9 volt battery and battery holder. (See photo)