Thursday, November 6, 2014

Plant Pigments and pH

I revisited a really fun experiment this fall during my introduction to acids and bases unit.   I tried it out with the library summer science program over the summer.  The community members enjoyed the experiment, and the results were exciting, so I decided to give it a try with my students.  Guest Post from Library Science Program

Our first look at the fascinating world of natural pigments was the classic experiment with red cabbage juice to test the pH of household substances.  The colors from the cabbage juice are just fantastic, red, pink, purple, blue, green, and yellow!  You can make your own cabbage juice at home by simple boiling some chopped up red cabbage in water.  The dark purple liquid is like gold when it comes to universal pH indicators.

During the next lab period we extracted pigments from colored fruits and vegetables.  (By the way, I usually make a big batch of cabbage juice, so this is their first experience with the extraction part of the experiment.)  It's pretty simple to do:  chop the fruit, boil it in just enough water to cover the fruit, and collect the colored liquid.  I brought in grapes, apples, cranberries, beets, red onion, tomato, red pepper, and other colored plants.  Each group extracted a different pigment, and then they shared with each other so the kids could test several different pigments.  The kids tested their pH sensitivity with a range of buffers solutions of pH from 2 to 12.  The results were absolutely wonderful!  The plants gave a beautiful range of colors in the buffer solutions, including pink, blue, green, yellow and red.  None of the pigments were as wonderful as the red cabbage, but we found a couple close seconds.  Here are some of the photos my students collected from the day.  You can look at one of the lab presentations from a group for this lab at this link:  Chase-Donze Pigments Lab

Extracting pigments from beets is very easy!

These boys are boiling their cranberries in water.

Plum pigment gave similar colors to grapes.