SC 130 Physical Science laboratory 13: Floral pigments as litmus tests for acids and bases

Notes for spring 2008: The chromatograph appears to have failed, despite prior work suggesting it could be done. The only difference was the use of a rock pounder in the functional chromatograph and the use of a mortar and pestle in class. Not enough crushing? The upshot is that pens or MM's would work better and this section of the lab was effectively not done.

Need more substances to test next term: ammonia, cream of tartar, acetone, drano...Could use more droppers.

Post-lab marking notes: Students remain unclear on acids versus bases. That concept in and of itself appears to be sufficient for the laboratory. Drop the chromatograph. Label the "known" substances more clearly. "Lime. Citrus fruit. Sour. Known acidic solution. Baking soda. Bitter. Known basic solution." Test more substances. Dilute bleach to see if oxidizing effect can be reduced. Test neutral fluids such as rubbing alcohol, vegetable oil. Dilute drain cleaner. Look for and acquire other substances such as cream of tartar, baking powder, coralline lime powder.

Coleus works almost better than Hibiscus tiliaceus. Early morning H. tiliaceus does not produce as much pigment as afternoon H. tiliaceus. Cream of tartar was impossible to find spring 2008, and both limes and baking soda were scarce on island the day before the lab.

Spring 2008 lab report follow-up: Students thought the floral fluids were acid or base and that we were testing them to see which were acidic and which were basic. Misunderstood the whole role of a "known" as used to find a best possible litmus fluid.

This lab needs further refinement, the language below and comment outs, prior to fall 2008 run. The three phase piece was added for 11:00 and really helped. The coleus made an excellent indicator. Maybe phase one should be tossed and coleus grown prolifically on campus?

This laboratory explores the use of floral and leaf pigments to whether a substance is an acid, bases, or neutral. This section of the laboratory explores whether flower petal pigments are good indicators of acids and bases, and if so, which flowers work best. To produce our flower petal test solutions the petals will be boiled in water.

In the English language acids are said to be sour or tart. Bases are often said to be bitter.


There are three phases to this laboratory.

  1. In the first phase you will gather flowers to use as tests for whether a substance is an acid or base. Pick common flowers. Do not pick flowers that belong to someone. Do not pick the orchids in front of the library or other rare flowers. You might also try colorful leaves, again, avoiding rare plants.
  2. In the second phase you will determine which flower produces the best floral fluid for determining whether something is an acid, base, or neutral. After boiling the petals, the fluid will be tested with a known acid and a known base. You are looking for a flower fluid which shows a distinct and different color change for known acid and the known base. In this lab lime juice is our known acid and baking soda is our known base.
  3. In phase three you will use that one "best" flower fluid to test liquids to determine if they are an acid, base, or neutral. When working with test tubes, be sure to rinse them well between tests. Be careful, some unknowns are poisonous, others can burn your skin.

Make a table [d][t][a] of your results for the unknowns noting the color change and the conclusion (acid, base, or neutral).

Use a flower petal solution that changes color in a consistent way for acids or bases. Use the solution to analyze [a] whether the following are acids or bases (additional compounds might be made available on lab day):

Conclusion [c]

[c] Conclusion. Discuss what flowers showed the most distinct color change for the known acid. Discuss what flowers showed the most distinct color change for the known base. Discuss any difficulties you encountered. Discuss any sources of potential error.