How to Neutralize the Reaction of Acids and Bases

Elements have different chemical properties. Some common elements are acidic whereas others are alkaline; combining acidic elements with alkaline base elements results in the neutralization of the two elements and the formation of a stable element such as a salt. Students demonstrate acid/base titration when they make baking soda volcanoes, and you can also use color change to indicate chemical changes from acid to bases.

Things You'll Need

• Vinegar
• Ammonia
• Measuring cup
• 2 cups chopped red cabbage (for pH indicator)
• One quart glass bowl
• Plastic strainer
• 3 glass bowls
• One tsp. measuring spoon
• Eye dropper

Instructions

Making the Cabbage pH Indicator

1. 

   Red cabbage contains anthocyanin compounds that are sensitive to pH.

   Place the plastic strainer inside the one-quart glass bowl.

2. Place the chopped red cabbage inside the plastic strainer.

3. 

   Boiling water releases the anthocyanin compound from the cabbage.

   Pour 2 cups of boiling water over the cabbage. Let it sit for ten minutes to allow the Anthocyanin compound to leach out of the cabbage. According to the University of Minnesota, red cabbage contains an anthocyanin compound that is sensitive to acids and alkaline substances.

   When exposed to acids, the compound changes color, and the color change can be used to indicate a substance's pH, how alkaline it is.

4. After ten minutes have passed the liquid in the bowl will be a reddish color. Lift out the strainer and discard the cabbage. The liquid left in the bowl is now a chemical pH indicator.

Use Color Change to Demonstrate Acid/Base Neutralization

1. 

   Use clear glass bowls so that you can watch the color changes.

   Use the measuring cup to measure 1/4 cup of vinegar and pour it into one of the clear glass bowls. The vinegar is the acid solution you are going to use in this demonstration.

2. Measure 1/4 cup of ammonia and pour it into a second glass bowl. The ammonia is an alkaline substance and is the base for this experiment.

3. Use the eye dropper to add red cabbage pH indicator to the vinegar until it turns red.

4. Add ammonia to the vinegar one teaspoon at a time, using the teaspoon measure, and observe the color changes. By the time you have added about half of the alkaline ammonia base to the vinegar the color will have changed from red to purple.

5. Add more of the ammonia one teaspoon at a time and continue to observe color changes. When all of the ammonia is added to the vinegar, the acid will have become neutralized, and the mixture will now be green in color.

   The anthocyanin in the cabbage juice indicates changes in the mixture's pH balance from red and completely acid to green, indicating an alkaline substance.

Tips & Warnings

• Many other plants contain anthocyanin compounds. Beets, apples, and radishes all contain the pH-sensing compounds.

• Be careful when mixing chemicals of any kind. Some mixtures can produce volatile reactions or toxic fumes. Always wear protective eye wear and know exactly what you are doing when working with chemicals.

References

• University of Minnesota: Red Cabbage Acid Base Indicator
• University of Vermont: Notes on Acids and Bases
• City University Ney York: Acids Bases and pH

Resources

• Montana Tech: Make a Chemical Volcano