Floral pigments as litmus solutions
Laboratory thirteen in physical science had the students collect flowers from around campus, produce floral solutions by boiling in water, and then test to see which floral solutions changed color for both a known acid and a known base.
The ideal flower is one that turns different distinct colors from the original floral solution color for both acids and bases. A less ideal situation is in which one floral solution changes in a distinct way only for acids while another floral solution changes only for bases.
Jeremiah tests a floral solution against the known acid. The laboratory uses a variety of local key limes as the known acid. Baking soda is the known base. This term I wrapped up Wednesday lecture with the atomic structure of hydrogen and hydronium ions, providing a nice segue into this laboratory. Having crashed and dashed through electron orbitals and filling, diagrams of HCl and NaOH provided the jumping off point for introducing H+ and Cl-.
Tracy Ann, Caroline, and Patsipa consider their collection of five floral solutions. On the table are the purple flowers of Spathoglottis plicata Blume (Philippine ground orchid) and the yellow flowers of Sphagneticola trilobata (L.) Pruski (previously misidentified as Wedelia trilobata (L.) Hitchc. and still listed in many sources this way). The ground orchid solution is a sharp royal purple and changes to a 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.
In past terms the Spagneticola has also proven useful, although I was not directly aware of any group actively testing the flower this term.
Kasinta displays color changes in her floral fluids.
For the first time I brought in Alpinia purpurata. 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.
Irene observes as Silver Rose tests Pine Sol (yellow variant), Cheryl and Peter test ammonia and diluted bleach, while Kasinta tests Rolaids using a watch glass. 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.
Solenostemon scutellarioides (Coleus) was used only in the 11:00 section. I also held off until 11:00 to send the students to retrieve Hibiscus tiliaceus. Prior experience has taught me that at 8:00 the blooms are neither fully opened nor have the necessary litmus compounds developed. Although the flower is bright yellow, the flower produces a dark purple solution - the same color the flowers turn after they fall off the tree, and the same color seen on the inside of the very base of the petals when the flower is on the tree.
Angie's floral solution displays a lack of color change, indicating a neutral pH.
Leslie and Brilinda compare and discuss two basic results - there were subtle differences in the colors. The test tube on the left had an olive tinge while the test tube on the right had a bluish tinge. Both solutions were otherwise almost black in reflected light. Floral litmus solutions do not always act in the same way to different bases. In general acids tend to change what are likely to be anthocyanin compounds pink, hot pink, fuchsia, or magenta colors. Response to bases can be much less consistent with colors ranging from olive greens, dark greens, steel blues, blues, and variations on black. In some instances even yellows are generated.
This laboratory is an odd laboratory which featured a full write-up. Due to the upcoming easter break, the lab will be due in three days on Monday.
The ideal flower is one that turns different distinct colors from the original floral solution color for both acids and bases. A less ideal situation is in which one floral solution changes in a distinct way only for acids while another floral solution changes only for bases.
Jeremiah tests a floral solution against the known acid. The laboratory uses a variety of local key limes as the known acid. Baking soda is the known base. This term I wrapped up Wednesday lecture with the atomic structure of hydrogen and hydronium ions, providing a nice segue into this laboratory. Having crashed and dashed through electron orbitals and filling, diagrams of HCl and NaOH provided the jumping off point for introducing H+ and Cl-.
Tracy Ann, Caroline, and Patsipa consider their collection of five floral solutions. On the table are the purple flowers of Spathoglottis plicata Blume (Philippine ground orchid) and the yellow flowers of Sphagneticola trilobata (L.) Pruski (previously misidentified as Wedelia trilobata (L.) Hitchc. and still listed in many sources this way). The ground orchid solution is a sharp royal purple and changes to a 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.
In past terms the Spagneticola has also proven useful, although I was not directly aware of any group actively testing the flower this term.
For the first time I brought in Alpinia purpurata. 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.
Irene observes as Silver Rose tests Pine Sol (yellow variant), Cheryl and Peter test ammonia and diluted bleach, while Kasinta tests Rolaids using a watch glass. 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.
Solenostemon scutellarioides (Coleus) was used only in the 11:00 section. I also held off until 11:00 to send the students to retrieve Hibiscus tiliaceus. Prior experience has taught me that at 8:00 the blooms are neither fully opened nor have the necessary litmus compounds developed. Although the flower is bright yellow, the flower produces a dark purple solution - the same color the flowers turn after they fall off the tree, and the same color seen on the inside of the very base of the petals when the flower is on the tree.
This laboratory is an odd laboratory which featured a full write-up. Due to the upcoming easter break, the lab will be due in three days on Monday.
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