Percent Ionization

Brief Description: 

Visualize the percent ionization of an acetic acid solution

Explanation of Experiment: 

Strong acids ionize completely when they are dissolved in water, while weak acids ionize only slightly.  As an example, glacial acetic acid has an acid dissociation constant of 1.75 x 10-5.  A 10 M solution of acetic acid has a percent ionization of only 0.132 %.  However, a 0.10 M solution has a percent ionization of 1.32 %.  In this demonstration, the relative ionization of acetic acid is visualized using a light bulb conductivity apparatua.  Initially only slightly ionized (0.132 %), the ionization increases as more water is added and made available for the ions to dissociate.  The increase in ionization is visualized by the light bulb glowing more brightly.

Materials Preparation: 
  • 100 mL glacial acetic acid 
  • 100 mL deionized water 
  • 250 mL beaker
  • Conductivity apparatus with light bulb
  • Stirrer

 

Presentation: 

Add 100 mL of glacial acetic acid to a 250 mL beaker.  Immerse the conductivity apparatus electrodes into the acid.  Plug in the apparatus - the light should barely glow.  Add deionized water to the beaker in approximately 20 mL portions and stir the resultant solution with the glass stirrer.  The more dilute the acid, the better it conducts and the brighter the bulb glows.

Hazards: 

Use care when handling glacial acetic acid.  It is corrosive to skin and tissue and is moderately toxic by ingestion and inhalation.  Wear chemical splash goggles, lab coat, chemical resistant gloves.

Disposal: 

Neutralize the acid solution using sodium bicarbonate and rinse the resultant solution down the drain with plenty of water.

General Concept:

Type of Reaction:

Primary Reference: 
Bilash, B., Gross, G.R., and Koob, J.K., A Demo A Day, Volume 2 - Another Year of Chemical Demonstrations, Flinn Scientific, Inc., 1998 p. 204