The winter season is almost upon us. That means thoughts of holidays, hot chocolate, and Poinsettias. In chemistry class, you can use Poinsettias to introduce the concept of pH. Whether you are studying acids and bases, or simply looking at chemical changes, being able to observe changes in pH is an important tool for your budding chemistry students.
A Poinsettia is one of many plants containing pigments that respond to changes in acidity.
You can take the mystery out of litmus paper and pH indicators by having the student create their own Poinsettia pH paper. The red pigment from deeply colored poinsettias can be extracted and used to make paper strips to test whether a liquid is an acid or a base.
To make the Poinsettia pH paper:
- Cut the flower petals (actually specialized leaves called bracts) into strips.
- Place the strips into a beaker.
- Add enough water to cover the plant material and simmer on a hot plate.
- Filter the liquid into another container and discard the solid plant matter.
- Saturate a piece of filter paper with the poinsettia extract.
- Allow the filter paper to dry and cut the colored paper into test strips.
Now you can use the strips to test the acidity and basicity of solutions. To make the activity more meaningful, you could construct a pH chart for your plant extract paper. Using some stock solutions of 0.1 M HCl and 0.1 M NaOH, you can prepare solutions of different pH values. Your students can quantity the pH of the new solutions with a Wireless pH sensor. Now that they have solutions of a known pH, they can create a pH color chart with the poinsettia paper. (The color range for acids and bases with depend on the particular plant.)
|Poinsettia pH paper|
With this brief activity, you have the opportunity to take a holiday tradition and turn it an engaging and educational experience.