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    Poinsettia pH Paper

    Kids, here's a way to use holiday plants for science! Many plants contain pigments that are responsive to changes in acidity. An example is the poinsettia plant, which has colored leaves called bracts (they aren't really flowers). You can extract the red pigment from bright-red colored poinsettias and use it to make your own pH paper strips to test whether a liquid is an acid or a base. 

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    Chemists use a pH scale to measure the extent to which a solution is an acid or a base.  The smaller the number on the pH scale, the more acid is the solution, and similarly, a liquid that measures high on the pH scale is considered basic.  Neutral solutions, such as tap water, measure close to 7 on the pH scale, while acids typically measure between 1 (very acid) and 6, while a solution measuring between 8 and 14 are basic, with a number above ten is very basic, such as a solution of lye or caustic soda.

    Materials

    • poinsettia 'flower' leaves
    • microwave proof beaker or cup, and a shallow bowl
    • a microwave oven
    • a strainer
    • scissors
    • filter paper or coffee filters
    • vinegar (dilute acetic acid)
    • baking soda 
    • window cleaner with ammonia

    Procedure

    • Cut the red leaves into strips or chop them in a blender. Place the cut pieces into a beaker or cup.
    • Microwave the chopped leaves with a small amount of water for about a minute, stir, and allow the mixture to steep, like a tea, for 15-20 minutes.
    • Strain the liquid into a shallow bowl. Discard the plant matter.
    • Saturate clean filter paper with the poinsettia solution. Allow the filter paper to dry on a plate. You could put them into the microwave for a minute or two to dry. Cut the colored paper with scissors to make thin, rectangular, pH test strips.
    • Make a solution of a weak base by dissolving about a teaspoon of baking soda (NaHCO3) in a half glass of water.  Don't worry if not all of the baking soda dissolves in the water.
    • Use a dropper or toothpick to apply drops of weak acids or weak bases to a test strip. Or you can dip the strip into the liquid. The color range for acids and bases will depend on the particular plant. A pink test strip from a red poinsettia should yield a gray or blue color for bases; for acids the color won't change much because they appear pink as well. Examples of weak acids include vinegar, clear soda and lemon juice. Examples of weak bases include the baking soda solution or window cleaner with ammonia. Try a variety of solutions around your house, even just water, to see where they compare in the pH color spectrum.
    • Another way to use your pH paper is as a color-change paper. You can draw on pH paper using a toothpick or cotton swab that has been dipped into the acid or base.

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    References:

    YouTube Video of the process:   http://www.youtube.com/watch?v=dYOcCJPcXyM

    Anne Marie Helmenstine, PhD: http://chemistry.about.com/od/chemistryblogs/a/poinsettia.htm

    To view all past “ChemShorts for Kids”, go to: http://chicagoacs.org/articles.php?article_category=1

    The Primary Education Committee of the Chicago Section ACS presents this column and hopes it will reach young children and help increase their interest in science. Please print it out and pass it on to your children, grandchildren, or elementary school teachers. Teachers are encouraged to incorporate the projects in this column into their lesson plans.