Making Cabbage pH Indicator

RED CABBAGE pH INDICATOR RECIPE

2 medium sized red cabbages
a blender
hot boiling water
fine sieve
funnel
mason jars with lids

This recipe produces at least 2L of red cabbage juice. Roughly chop the cabbage into small chunks. Place 2 cups in a blender and cover with boiling hot water. Cover and pulse for a few seconds. Add another cup of cabbage and pulse again until all chunks have been reduced to thick smoothie-like consistency. Let steep for 10 minutes. After 10 minutes, pour the cabbage mixture through a sieve and let the liquid drain into a mason jar. Repeat the process until you have used all of your cabbages. Let the juice cool and cover tightly. To check pH, sample the cabbage juice with vinegar and bleach. This entire process took me about 30 minutes to complete.

This weekend, I found myself in a predicament. I was researching labs on cellular respiration, and it seemed that many of the labs required bromothymol blue solution. Bromothymol blue solution is an indicator, and a chemical that I do not have available on hand. Let’s rephrase that: I have no chemicals available at all. I work in a new laboratory space that does not include a fume hood or storage space for chemicals, so it takes a lot of creativity and research trying to figure out safe substitutes for lab.

In class, we were finishing our unit on Photosynthesis and wrapped up with a lab using Elodea plants submerged in test tubes. Usually, learning the formula for photosynthesis can be difficult for scholars so I rely on labs on helping them make tangible connections between formulas and concepts in class. I wanted to start our unit on Cellular Respiration with a lab using yeast and bromothymol solution. This way the scholars can make the connections between the two processes and their formulas. That’s when I hit a dead end: no bromothymol blue solution.

I thought about ordering online, but even with expedited shipping and handling, the solution would not make it to school on time for the day of the lab. So, I did what I always do when I am in a predicament— I sent out an SOS email to my NSTA Science Teacher Academy mentor, to science community forums, and local science teachers in the area asking for alternative labs or suggestions. One of my PLN members from the NSTA Biology List serves responded, and suggested I make an acid-base indicator out of red cabbage.

Bingo! I thought about a session I attended earlier this month from an all-day Lab Day conference at The College of Saint Rose. The presenter shared 5 life science labs, one of which was called “Micro-Mood Necklaces”. In this lab, she used red cabbage juice and yeast to show the process of fermentation. The solution was put into micro-tubules strung onto necklaces, and the solution changed color over time as the yeast reacted. The color change may not be as dramatic as it would be with bromothymol blue solution, but there would still be a color change and that was what I wanted my scholars to witness with the cellular respiration lab. Whew!

Needless to say, I rushed to the grocery store and added several heads of red cabbage to my weekly grocery list. The fiancee became nervous, imagining it was another one of my creative spurts of culinary inspiration. He only relaxed after several repeated assurances that there will be no red cabbage in our dinner menu. Anyways, I hope the red cabbage indicator works. I am interested to see how the cellular respiration lab turns out this week.