Science Poetry

Indicating Interest

“The careful routines of titrations:
Through meticulous applications,
Technique’s operator
Can use indicator
To quantify neutralizations.”  

The 3 April 2020 poem returned to the limerick form with a summary of a common introductory chemistry experiment: an acid-base titration.  

“The careful routines of titrations… /
In my experience, many students have strong memories of titrations from previous chemistry courses: measuring out the volume of a reactant dispensed through a buret, a precise piece of glassware; carefully swirling around the resulting mixture in a flask, watching for a tell-tale color change.           

“Through meticulous applications, /
Technique’s operator /
Can use indicator /
To quantify neutralizations.”  
Titrations can be used to investigate multiple types of reactions, but many are used to explore the reaction of an acid with a base.  Acid-base reactions are generally called neutralizations, and color-changing, pH-sensitive indicators are used to investigate these experiments.  

In one common type of acid-base titration, a flask is prepared, containing an acid and phenolphthalein indicator, which is clear in solutions with acidic pH.  When the base delivered from the buret has neutralized the acid in the flask, the indicator turns pink, showing that a basic pH has been reached.  If the “technique’s operator” is adept at the experimental set-up, the resulting data about where the color change occurred can “quantify neutralizations”: yielding information about the stoichiometry of the reaction, the molar mass of the acid, and other interesting information.  (While the full chemistry of phenolphthalein is more complex than this brief summary, this narrower pH window is what’s typically investigated in an introductory chemistry course.)  

Titrations require “meticulous applications”: for the specific case described here, the difference between a very pale pink color (the result of a successful experiment) and a more magenta-ish hue involves only a few drops of delivered titrant.  It often requires multiple attempts for an investigator to achieve the most exact results possible, in these experiments.