Dry Ice and Acid Base Indicator Activity

 

Written Dr. Andrew Greenberg

Institute for Chemical Education and Nanoscale Science and Engineering Center

University of Wisconsin-Madison

 

Purpose: The goal of the lab activity is to teach students how to use the Submersible Audible Light Sensor to distinguish changes in color due to change in the pH of a solution.

 

Learning Objectives:

            1. Learn how to operate the SALS sensor

            2. Learn how an acid base indicator works

            3. Learn how dry ice changes the pH of an ammonia solution

4. Learn to distinguish different colored solutions using the SALS sensor.

 

Materials:

            1 L Household Ammonia

            1 lb Dry Ice

            1 metal mesh grid with hole for sensor

            1 cup sugar

            1 600 ml Beaker

            Universal Indicator Solution

            1 Winter glove for handling dry ice

            1 SALS sensor

            1 roll of clear plastic wrap

            1 light box

            1 L Water

 

Procedure:

 

  1. Fold down the corners of the mesh grid so the hole is approximately in the center of the grid.

 

  1. Place the grid into the empty 600 ml Beaker

 

  1.  Fill the beaker approximately half full with water.

 

  1. Add some universal indicator solution to the beaker until you can see color throughout the solution. You many need to stir the solution.  The color will be anywhere from green to orange depending on the pH of the water.

 

  1. Add ammonia to the beaker until the solution turns purple, if the color is very faint add more universal indicator solution.

 

  1. Cover your light box with a coat of plastic wrap.

 

  1. Place the beaker on top of the light box and turn on the light.

 

  1. Turn SALS Device on using the power button. (see attached diagram of Device).

 

  1. Place the sensor of the SALS device inside of the hole of the grid making sure it is below the level of the grid but not touching the bottom of the beaker.

 

  1. Push the Play button to hear the tone this color and note the starting color of the solution.

 

  1. Store the tone in the memory by hitting the Store button and then Memory 1.  This allows you to compare this tone to the tones of the next concentrations. (CarefulŠthere is also a Memory 2 so donšt get confused)

***BE SURE TO REMEMBER TO STORE TONE IN MEMORY AND WHICH MEMORY IT IS IN!

 

  1. Wearing a winter glove drop a piece of dry ice into the beaker making sure it lands on top of the mesh grid.

 

  1. Push the Play button on the SALS device to hear the tone.

 

  1. Continue to press the Play button and note the tone of the output. You should hear a gradual change in the tone. This represents a change in pH of the solution.

 

  1.  When the tone stabilizes store this tone in the memory by hitting the Store button and then Memory 2. 

***BE SURE TO REMEMBER TO STORE TONE IN MEMORY AND WHICH MEMORY IT IS IN!

 

  1. Compare the tone of this pH with the first pH stored in Memory 1.

 

  1. The tone in Memory 1 represents a basic solution and the tone in Memory 2 represents an acidic solution as measured using universal indicator solution.