Floral litmus solutions

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

Mandylae pours hot water into her flowers with Iva Nicole and Mayleen Route in the back left

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).

Anjannette and Tristan test bleach while Regina Pelep looks on

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.

Anjannet Fredrick

Sphagneticola trilobata this term again went from bright yellow to a deep orange for bases, but had only a shift in saturation for the known acid.


A red variety of Hibiscus rosa-sinensis turned magenta for acids, and turned green for ammonia and other bases, but did not change color for the Arm & Hammer Baking Soda. The baking soda was a new batch of baking soda, so I am baffled. That variety has reacted with baking soda in the past, turning a dark greenish blue. I am thinking I should shift to ammonia as the known base as ammonia seems more predictable and easier to read than baking soda. Baking soda does not really dissolve well in the small amounts of liquid being using in the lab, resulting in a cloudy whitish suspension in many cases.

Mandylae and Regina Pelep

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.

Sasha tests her floral litmus solution for a reaction to a known base: baking soda

This was the first term that I had to turn to karer tik, an orange fleshed variety of key lime. Despite the flesh color and small size, just four of the karer tik produced a large beaker of strongly acidic solution.

Tristan had fun with density

Pelida, Dorothy, Kimsky, and Joanna Robert test unknowns

Joanna and Aimina working together on unknowns


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