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Seasonal 4-H Science: Poinsetta pH Paper

You may have made your own pH indicator out of red cabbage in science class, but did you know that you can make pH paper out of poinsettias?  Many plants contain pigments (special colored cells) that are responsive to changes in pH.  You can extract the pigment from red poinsettias to make your own pH paper at home to test whether a liquid is an acid or a base.  “pH” stands for potential Hydrogen and is a measure of the acid/alkaline balance of a substance.  Scientists use this measurement in a variety of fields to monitor health of humans, plants, and animals. pH is also an important measurement for maintaining our water quality.

Poinsettias are native to Mexico and Central America.  In the US, they are used as annual decorative plants for the winter holidays, but they can be grown as a perennial in warmer climates.  They are available in a variety of colors ranging from white to deep red.  The so-called ‘flowers’ are actually special leaves called bracts; the real flowers are tiny and usually yellow.  For more information on how to select and care for poinsettias, visit the UF IFAS Extension website at: http://solutionsforyourlife.ifas.ufl.edu/hot_topics/lawn_and_garden/poinsettias.html#varieties.  Note: Poinsettias are in the milkweed family, and some people are sensitive to the milky sap that comes out when you break off a leaf.  Be sure to wash your hands after handling the leaves, and do not touch your face, eyes, or mouth while making your pH paper.

To make Poinsettia pH paper, you will need:

  • poinsettia bracts
  • scissors or a blender
  • ½ cup boiling water
  • 2 cup liquid measuring cup
  • coffee filters
  • rubber band
  • toothpicks or cotton swabs
  • vinegar or lemon juice (an acidic solution to test pH)
  • baking soda solution (1 tsp. in one cup of water, a base solution to test pH)
  • adult supervision

Cut the bracts into strips or ask a parent to chop them in a blender. Place the cut pieces into measuring cup.  Add just enough boiling water to cover the plant material. Allow the solution to steep until the color is removed from the plant (this usually takes 10-20 minutes).  Cover a cup with a clean coffee filter and secure with a rubber band.  Slowly pour the liquid into the cup, then discard the plant matter.  Remove the rubber band and filter paper and discard.  Dip a clean coffee filter into the filtered poinsettia solution.  Allow the filter paper to dry. You can cut the colored paper with scissors to make pH test strips, or leave the filter whole to use a color change paper.  Use a toothpick or cotton swab to apply a little liquid to a filter paper. The color range for acids and bases will depend on the particular plant.

Create your own pH scale by researching the known pH of common house-hold liquid such as vinegar, lemon juice, orange juice, soda, etc.  Test each liquid to determine the color the pH level produces; or design an experiment to find out what happens if you dilute the vinegar or baking soda.  Does it change the pH?

4-H is the youth development program of UF/IFAS Extension and is available in all 67 counties in Florida.  Youth involved in 4-H science programs apply science, engineering, and technology skills to their projects, develop science literacy workforce skills, and pursue education and careers related to science resulting in a workforce that will create a viable economy and communities for Florida.   According to the Tufts University Study on Positive Youth Development, 4-H youth are more likely to: Report better grades, higher levels of academic competence, and an elevated level of engagement at school; are nearly two times more likely to plan to go to college; are more likely to pursue future courses or a career in science, engineering, or computer technology; and have higher levels of female involvement in science programs.   4-H is open to all youth, ages 5-18, regardless of gender, race, color, ethnicity, nationality, creed, or disability.