Poinsettias are beautiful holiday plants.  But when the holidays are over, what can you do with them?  It turns out that poinsettia leaves, much like red cabbage leaves, make an excellent pH indicator!

First of all, what is pH?  The term “pH” stands for “power of Hydrogen” and is a measure of how many Hydorgen ions are in a liquid or solution.  Acids have a lot of hydrogen ions and bases have very few.  The scale runs form 1 (extremely acidic) to 14 (extremely basic) with water in the middle at 7 or neutral.

pH indicators are great because you can use them to measure the pH of ANY liquid.

To make a pH indicator out of a poinsettia, chop up about a cup of the red leaves – scissors are good for this.  Pour another cup or so of boiling water over the leaves and let them steep for 20 minutes or more.  Then pour everything through a strainer to separate the leaves from the liquid.  This liquid is the pH indicator!

When added to a liquid this indicator will turn red/dark pink in the presence of acids and greenish brown in the presence of bases.

You can put it directly into any clear liquid of which you want to explore the pH – OR you can make paper strips to dip in the liquid.  This is much better for coffee or orange juice or other liquids that already have a color.  Just soak coffee filters in the pink poinsettia leaf liquid and then dry them out and cut into strips.

So how can you use this for a science fair project?

You could investigate what sorts of plants have flowers or leaves that also make good pH indicators.  Try red cabbage leaves, kudzu flowers (!), geranium, petunias, rose petals,  or other plants with purple/pink/red pigments. The particular pigment that causes this effect is anthocyanin.  Some foods to try are blueberries, cherries, blackberries, beets and carrots. Even yellow turmeric turns red in a basic solution!

pH indicators can also be a useful tool for all sorts of questions involving water quality or for identifying properties of liquids.

Poinsettia Indicator
Tagged on: