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Strong and Weak Electrolytes (4 Favorites)

LAB in Conductivity. Last updated April 25, 2019.


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

  • Big Idea 2: Chemical and physical properties of materials can be explained by the structure and the arrangement of atoms, ions, or molecules and the forces between them.
    • 2.1 Students can predict properties of substances based on their chemical formulas and provide explanations of their properties based on particle views.
    • 2.9 The student is able to create or interpret representations that link the concept of molarity with particle views of solutions.

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)
File

Low-cost conductivity tester. (Credit T. Koehn)

For the Student

Lesson

Background

We have seen that strong electrolytes contribute a lot of ions in solution and are therefore good conductors of electricity, while weak electrolytes contribute few ions in solution and are poor conductors of electricity. We can test the conductivity of a solution by using a diode conductivity tester. If the diode lights up brightly the solution contains a strong electrolyte and if the diode barely lights up, the solution contains a weak electrolyte.

Materials

  • Four Test Solutions
  • Wash bottle or beaker of distilled water
  • Wash bottle or beaker of tap water
  • Conductivity Tester
  • Paper towels

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.

Procedure

  1. Write a description of the solution that is in each cup in the data table below.
  2. Clean the wires of the diode tester in distilled water before placing the ends in the first cup. Record your observations in the table below.
  3. Before moving on to the next cup, clean the wires of the diode tester with tap water, then distilled water.
  4. Place the ends of the diode tester in the cup. Record your observations in the table below.
  5. Repeat step 3 and 4 for the remaining cups.

Observations

Solution Conductivity

Analysis

  1. Based on the data collected, which of the solutions are the strongest electrolytes? Which are the weakest?
  2. What to the results indicate about the ions present in each of these solutions?
  3. Which of these solutions would you predict to contain ionic bonds? Which ones contain covalent bonds?