Floral litmus solutions

In physical science laboratory thirteen the students use floral litmus solutions to determine whether household substances are acids, bases, or neutral.

Jayleen Alex, Trevalouva, Redsea working on the unknowns

The students bring in flowers. I do not provide guidance as to which flowers to bring in, there is no simple predictor for which flowers will work in any given term or at a particular time of day. Some flowers work better latter in the day (Hibiscus tiliaceus) while others work some terms and other terms do not work (Sphagneticola trilobata). Spathoglottis plicata tends to be reliable if freshly picked. And some flowers do not produce any pigment (Ixora casei, Saraca asoka. If boiled long enough, I. casei produces a light pink solution which can only detect bases.).

Johsper working with two flowers: one that detects bases, one that color changes with acids

Each floral litmus solution is first tests against a known acid (local lime fruit, karer tik this term) and a known base (baking soda) to determine whether the flower can detect acids and bases. The students are told to cue in on the hue angle and to ignore changes in saturation or luminosity. Changes in saturation or luminosity - terms from laboratory ten - are not reliable, reproducible indicators.

Trevalouva, Mike Selestine, Elymore

Sphagneticola trilobata this term did not behave well, the deep orange in the presence of a base was not clearly seen.

Justice works with AJ on determining a color

This term the Hibiscus rosa-sinensis performed well, as this flower has in the past. Spring term 2017, however, H. rosa-sinensis did not perform as expected. That remains an unexplained anomaly. This term I did not run a demonstration at 8:00, opting to let the lab progress somewhat more organically. At 11:00 I ran a demonstration, using Plectranthus scutellaroides leaves from the house. These performed spot on as expected.


Mayleen Araisang with a color change for base

Once the lab partners have a working floral solution they work on determining whether household substances such as ammonia, bleach, cream of tartar, vinegar, hand soap, detergent, are an acid, base, or neutral.

Melsina testing her floral litmus solution

Amy-Lang with color changes

Overall this laboratory remains popular among students in term end surveys and continues to perform well as a laboratory experience. 

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