Julie Franzak

ELED 305-42

6/5/2007

Science Area: Chemistry

Concept: Acid/Base Reactions

Indicators

Overhead Activity

Materials:

3 clear plastic cups

Head of purple cabbage (coarsely shred)

Teaspoon

Paper towels

***Safety glasses

White vinegar

Ammonia

Water

 

 

State Goals:

11.A.2d. Use data to produce reasonable explanations.

12.C.2b. Describe and explain the properties of solids, liquids and gases.

Safety Considerations:

Do not allow students to handle ammonia.

Science Process Skills:

Observing & Communicating

Procedures:

1. Do prior to demonstration:

1. Boil shredded cabbage in a ½ a pot of water for ~10minutes.

2. Strain cabbage & refrigerate until ready to use.

2. Fill cups (about halfway) with each liquid.

3. Add 1 teaspoon of the boiled cabbage to each glass.

4. Observe the color changes

Vinegar- Red= Acid

Ammonia- Green= Base

Water- Purple= Neutral

5. Based on these color changes: try to predict whether other liquids are acidic or basic.

-Add the boiled cabbage to find out.

Extension:

1. Soak paper towels or white coffee filters in purple cabbage juice

2. Let it dry and cut into strips.

3. The strips should change color according to the type of liquid it’s dipped into.

Explanation:

pH is a scale that helps scientists determine how acidic or basic a solution is; what the pH scale is actually showing is how much hydrogen ion is present in a solution. The hydrogen ion causes a solution to be acidic. The pH scale ranges from 0 to 14; the more hydrogen ion that is present in a solution, the closer it is to 0. The less hydrogen ion that is present in a solution the closer the pH value is to 14. Solutions that have a pH value of 7 are said to be neutral and solutions that are below 7 are considered to be acidic. Those solutions with a pH value greater than 7 are basic.

Cabbage juice contain anthocyanins; when the juice of the cabbage is exposed to different pH solutions, the anthocyanins cause a different color based on the pH of the solutions. Very acidic solutions will cause the anthocyanins to turn red, neutral solutions will change to a purplish color and basic solutions will appear in a region of color between yellow and green.

Most household detergents are basic and most foods are acidic.

Source:

“Acidic and Basic Test”. http://www.canteach.ca/elementary/pysical9.html on May 25, 2007.

“Acid/Base Reactions and ‘Cabbage Indicator’”. http://www.iserv.net/~chargers/chem/sececabbage.htm on June 1, 2007.