Introduction

The conductivity apparatus is a display of ten panels of diodes which light up from left to right with increasing degrees of conductivity of the solutions, and is very effective in the lecture setting.  The conductivity of acids and bases and sugar, as well as any other solution the lecturer requests, is compared in this manner.  A popular demonstration is to show that glacial acetic acid does not conduct electrons, but as water is added, H+ is liberated, causing conductance.

Prior to Lecture  (prep time ~ 10 to 15 min.)

Assemble the following:

  • Conductivity apparatus
  • Any requested solutions (the most popular are 0.1 M HCl,  0.1M acetic acid, distilled water, glacial acetic acid (cover with Parafilm until used in demo), 1.0 M NaOH and 1.0 M NH3, mostly available premade on the reagent shelves).  Place in labeled 100 or 150 ml beakers.
  • Glass stir rod
  • 400 or 600 ml waste beaker into which to rinse probe Wash bottle of distilled water
  • Box of Kimwipes
  • Googles
  • Gloves

To Conduct Demonstration

  1. Have conductivity apparatus plugged in at the start of lecture.
  2. With one end of the probe cable plugged into the meter, dip the other end of the probe into the desired solution.
  3. After the reading is taken, rinse the probe thoroughly and blot dry with a Kimwipe before placing in the next solution.
  4. For the glacial acetic acid demo, dip the probe in the glacial acetic acid: there should be no lights on the display.  Gradually add distilled water to the acid while stirring with the stir rod.  The amount of conductance should increase.

Note:  There is a double light bulb conductivity meter available for this demo.  Some lecturers prefer it.  It has traditionally been stored on top of the black cabinet by the door of the   demo room.  Make sure no one touches the exposed wires while it is plugged in!

Demo Time: ~5 - 10minutes

Safety and Disposal

If using the light bulb conductivity meter, take care to prevent electric shock.  Don’t touch exposed wires!

The solutions may be sink disposed.

Acknowledgement:

Stewart Strickler, Spring 1987.