Floral litmus solutions

Physical Science SC 130 laboratory thirteen collected flowers and boiled them to generate floral litmus solutions. Some flowers generate solutions that function both as red and blue litmus paper simultaneously - that is they change to two different colors when a base or acid is added to the floral litmus solution.

John adds acid to his floral litmus solution, Merna Keller on the left. The laboratory uses a variety of local key limes as the known acid. Baking soda is the known base. Chemistry is a quick run from proton and electrons, basics of atomic structure, hydrogen to oxygen, and then the structure of hydrogen and hydronium ions, providing an attempt at a segue into this laboratory. This material always reminds me that physical science is a bizarre course, an assembled beast that has way too much material in it.

Brend adds acid to Spathoglottis plicata. Flowers that work as floral litmus solutions tend to turn magenta in the presence of acids. In the presence of bases the solution may turn blue, steel blue, green, dark blue-green-gray, or almost black.

Testing a basic substance. This term I remembered to bring in Alpinia purpurata which again worked extremely well. Experience had suggested that "waxy" flowers did not usually perform well in this laboratory. Although I was aware that the key compound which makes many of the flowers useful as litmus indicators are the anthocyanins, and that these are unrelated to the outer coating, my experience had been that waxy flowers on island either did not contain anthocyanins or they were hard to extract simply by boiling. Thus I was pleasantly surprised when the Alpinia yielded a full two-color changing litmus solution.

Lisa Lollaine and Ariel Maylea working with the unknowns. Once a functional floral solution is found, the students test of a variety of household compounds such as PineSol (yellow variant), ammonia, diluted bleach, drain openers, hand soap, and rubbing alcohol. The bleach has to be diluted or the color change is followed so quickly by a loss of color (the fluid is bleach after all) that the color change is hard to catch with the human eye.

Mindira and Moses check floral solutions to determine which, if any, detect acids and/or bases. Solenostemon scutellarioides (Coleus, leaf) was not available this year. The plant on the hill has died back. The Alpinia appears to be a good substitute.

Oneal checks unknowns. Much of the fun of this laboratory, if for no one other than myself, is to see how different flowers will react. Some flowers vary in their indication abilities with the time of day. Hibiscus tiliaceus usually does not work well early in the morning when it first opens. The flower works better by later in the day, closer to when it will fall off the tree in mid-afternoon.

Charleen Fernandez.
Alden Damarlane.


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