Tag: teaching

“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.    

“Our molecule’s geometry 
As sketched-out: asymmetric;
We also note an (overall)
Lopsided charge electric.
Electrostatic map thus shows,
Through densely different hues,
Unequ’lly shared covalent bonds:
Polarity ensues.”

The 2 April 2020 poem describes an electrostatic potential map, a visual, color-coded tool with which chemists can quickly assess the variation of electronegativity for the atoms in a given molecule. Understanding a molecule’s polarity (or lack thereof) is an important step in assessing its properties and reactivity. Determining whether a species is polar or non-polar overall can also be achieved via consideration of whether its covalent bonds are polar or non-polar.   

“Our molecule’s geometry /
As sketched-out: asymmetric; /
We also note an (overall) /
Lopsided charge electric.”
In considering a molecule’s polarity, we consider its geometry (shape) and its overall charge distribution; “sketch[ing] out” a molecule allows us to assess these properties quickly.    

Water, for instance, is famously polar.  It contains an oxygen atom and two hydrogen atoms, arranged in a V-shape.  The oxygen atom is highly electronegative: it strongly attracts its electrons to itself.  The oxygen atom takes on a partial negative charge.  Each O-H bond is “polar covalent” and the molecule’s charge distribution is, overall, “lopsided”: the electron density is shifted towards the oxygen atom.  Non-polar molecules can have bonds in which atoms share their electrons equally via non-polar covalent bonds (such as H₂, in which each hydrogen atom behaves identically).  They can also contain polar covalent bonds, if the symmetry of the molecule means these effects cancel one another out overall (as in CO₂, where the oxygen atoms are linearly arranged on either side of the central carbon atom).

This particular poem describes an asymmetric molecule with polar covalent bonds.   

“Electrostatic map thus shows, /
Through densely different hues, /
Unequ’lly shared covalent bonds: /
Polarity ensues.” 
For the molecule described here, an electrostatic potential map would show high electron density (electronegativity) in red and low electron density (electropositivity) in blue: “densely different hues.” Lines 1-4 previously established that the molecule does not have a symmetric geometry. Our takeaway is that our hypothetical species will have polar covalent bonds and be polar overall: “polarity ensues.”  

The inspiration for this poem was the similarity in sound between the final line and “hilarity ensues,” a common trope in entertainment writing.

“Red shift, blue shift:
Spectroscopic
Info proves a
Useful topic.
As the data
Tilt aesthetic,
Make conclusions
Energetic.”

The third poem posted on 2 March 2020 for Dr. Seuss Day was similar in structure to the second, again borrowing from “Red Fish, Blue Fish.”  Here, even the colorful theme of the first line persisted, as this verse highlighted the spectroscopic phenomena known as red and blue shifts.

Somewhat fittingly, this was the last poem I posted before quite a historic “shift” of its own kind: the move of our entire curriculum online in Spring 2020, during the COVID-19 pandemic.   

“Red shift, blue shift: /
Spectroscopic /
Info proves a /
Useful topic.”
A “red shift” is a phenomenon seen in multiple scientific fields.  For chemists, it indicates that the observed wavelength of electromagnetic radiation (EMR) seen for a characteristic signal in a sample has lengthened.  [Within the visible light spectrum (represented by the familiar rainbow of ROYGBIV), red light has the longest wavelength.]  Conversely, when a “blue shift” occurs, the observed wavelength has shortened.  

Multiple phrasings of these concepts can be expressed.  Because wavelength is inversely proportional to frequency and energy, a red shift also demonstrates a shift towards lower-energy and lower-frequency EMR; a blue shift also indicates a shift towards higher-energy and higher-frequency EMR.  (The most precise chemical terms for these effects are “bathochromic” and “hypsochromic,” respectively.  Intriguingly, these also fit the trochaic rhythm present in this poem!) 

For a chemist, this information often arises in spectroscopic investigations, “prov[ing] a useful topic”: giving insight into what type of structural effect in a molecule might increase or decrease the characteristic wavelength at which a particular peak or signal is observed.  For instance, an interaction that stabilizes a particular molecular motion would lead to lower energy and thus a longer wavelength observed for that characteristic vibrational frequency, as demonstrated via a red shift on the pertinent spectrum.      

“As the data /
Tilt aesthetic, /
Make conclusions /
Energetic.”
As stated above, if a sample is exhibiting a “tilt aesthetic” in its spectrum– the presence of a red or blue shift for a characteristic peak, via a fair bit of poetic license– a chemist can often infer important information about a chemical structure or make other “conclusions energetic.” 

“One C, two C:
Nomenclature!
Molecules’
Entitled natures.
Methane, ethane:
Name conventions 
Relay alkanes’
Size dimensions.”

Another Twitter poem from 2 March 2020 was the second of three poems written in honor of Dr. Seuss Day.  Unlike the first, which had mimicked the style of “How the Grinch Stole Christmas” in discussing Lewis structures (electron dot structures), the second echoed the staccato notes of “One Fish, Two Fish, Red Fish, Blue Fish” to provide an overview of organic chemistry nomenclature: how organic molecules are named.  

“One C, two C: /
Nomenclature! /
Molecules’ /
Entitled natures.”
Instead of “One fish, two fish,” this poem starts out with “One C, two C.”  The verse will look at two simple molecules, the first containing one carbon atom (“one C”) and the second containing two carbon atoms (“two C”).  Nomenclature involves naming (i.e., “entitling”) rules for molecules.        

This poem and the third Seuss homage (which will be posted in the next entry and uses a similar structure), were among the most difficult to compose of all these Twitter poems.  Each line is very brief, consisting of two trochaic feet; each syllable has to be carefully chosen.  This provides an intriguing analogue to the principles of chemical nomenclature, where every part of a compound’s name communicates a great deal of information.  

“Methane, ethane: /
Name conventions / 
Relay alkanes’ /
Size dimensions.”
“Alkane” is an organic chemist’s shorthand for a “saturated hydrocarbon”: a compound that contains only carbon and hydrogen atoms; it has single bonds only and thus the maximum number of hydrogen atoms bonded to carbon atoms.  This type of compound is denoted with the suffix “ane.”    

Methane is the alkane with only one carbon atom, corresponding to the first compound named in the first line of the poem; ethane is the alkane with two carbon atoms, corresponding to the second compound named.  Knowing what is meant by the “name conventions” also tells a chemist how many carbon atoms are in the carbon chain of a given alkane; the names “relay [the] size dimensions” of the compounds. (The title here borrows a line from yet another poet, reinforcing the fact that the depth of information available in a chemical compound’s name is considerable.)    

“With this 2-D depiction’s molecular art,
We’ll some insights on bonding begin to impart:
Atoms’ valence electrons arranged, as we do this.
(A rhyme scheme from Seuss, for the structures from Lewis.)”

Three poems were posted on March 2, which was “Dr. Seuss Day,” in honor of Theodore Geisel’s birthday.  The first of these 2 March 2020 poems employs roughly the same rhyme scheme as “How the Grinch Stole Christmas,” which is written primarily in anapestic tetrameter (a fact which leads to a rather grievous pun in this essay’s title).  This poem provides some background on Lewis structures, which are simple depictions of molecular compounds.    

With this 2-D depiction’s molecular art, /
We’ll some insights on bonding begin to impart…
Lewis structures (also called “electron dot structures”) are two-dimensional (“2-D”) drawings on paper rather than molecular models, dash-wedge notation, or any of the other three-dimensional representations that chemists use to explain molecular behaviors.  They are pictorial representations of compounds (“molecular art”) and provide initial insights into molecular structure via chemical bonding.  However, these structures provide simplistic views only: they “begin to impart” understanding, but a General Chemistry student will quickly supplement this view of chemical bonding with more complex discussions of three-dimensional structure, such as valence-shell electron pair repulsion (VSEPR) theory.     

Atoms’ valence electrons arranged, as we do this.
To draw a Lewis structure, we count the number of valence electrons in a given compound, then arrange those electrons via bonds (represented with lines) and lone pairs (represented with pairs of dots).  The goal is generally that the octet rule will be obeyed for all atoms in the structure: that through covalent bonds and lone pairs, eight valence electrons will surround each atom, so that each atom achieves a “full octet” and thus stability.  As with any rule, exceptions exist. 

(A rhyme scheme from Seuss, for the structures from Lewis.) 
This last line acknowledges both the punchline to the poem, revealing the concept of interest, and the homage in the poem’s style (“a rhyme scheme from Seuss”).  The anapestic tetrameter and amphibrachic tetrameter used here are most familiar to me from “How the Grinch Stole Christmas,” but the styles are closely associated with Dr. Seuss’s work and comic verse in general.  Aiming to fit a chemical discussion into this more complex setting was a fun challenge. 

“The elements: perpetually trending!  
Their table: conceptually tending
Some ranks qualitative
Regarding key data
Of species, location-depending.”    

The 12 February 2020 limerick belatedly highlighted National Periodic Table Day, which I had not realized existed until its celebration on February 7… at which point I saw many pertinent Twitter hashtags!   

“The elements: perpetually trending!”  
The first line acknowledges the play on words with “trending” in a social media context and in a chemistry context.    

“Their table: conceptually tending /
Some ranks qualitative /
Regarding key data /
Of species, location-depending.”   
Information about elements’ behaviors can be understood from a reading of the periodic table of the elements (PTE), as described in lines two through five.  

This is a poem in which the rhyme aligns fairly closely with the prose explanation.  The periodic table organizes (“conceptually tends”) a wealth of general chemical and physical data about the elements (their “ranks qualitative”).  In other words, once someone learns to read the PTE, they can use the placement of elements relative to one another to predict trends in these properties (“key data… location-depending”). 

For instance, atomic radius (which essentially corresponds to atomic size) decreases left to right across a row of the PTE and increases down a column of the PTE.  Thus, from looking at a periodic table, we know without having to research specific numbers that rubidium (Rb) would have a greater atomic radius than the element in the same column in the row directly above it: potassium (K).  Correspondingly, potassium would have a greater atomic radius than its neighbor directly to the right: calcium (Ca).  If we look these specific data up, we can confirm the trend: the respective atomic radii of Rb, K, and Ca are 235 picometers (pm), 220 pm, and 180 pm.  

Countless other relationships can be described, for a variety of physical and chemical elemental behaviors.  The PTE is an enormously useful reference tool, for scientists and science students around the world.         

“Procedures in bomb calorimetry
Take place in a setting of constant V.  
From the temperature change
In solution, arrange
Calculations for internal energy.”

The 27 January 2020 limerick describes the main mathematical aims of a chemistry lab technique called bomb calorimetry. The language is, unsurprisingly, less precise than I’d teach in class, but the poem provides an overview of the experiment!  

“Procedures in bomb calorimetry /
Take place in a setting of constant V.”  
Calorimetry experiments measure the transfer of heat energy; different types of calorimetry involve different types of experimental settings and instruments.  Constant-pressure calorimetry was generally described in a previous entry: if a lab vessel is open to the air, the pertinent chemical reaction occurs at constant (atmospheric) pressure; coffee-cup calorimetry is one common example.  

By contrast, this poem highlights constant-volume (“constant V”) calorimetry, or bomb calorimetry, in which a reaction occurs in a sealed metal container. A chemical sample is placed in this container (the “bomb”), which is then filled with oxygen; ignition of the sample via operation of the calorimeter causes a combustion reaction to occur.  

“From the temperature change /
In solution, arrange /
Calculations for internal energy.” 
The ending lines sum up many calorimetry calculations: information about a reaction is inferred from a measurement of the temperature change in the surrounding water. 

In constant-volume calorimetry, the oxygen bomb is placed in a water bath in the larger calorimeter.  The “in solution” phrase is linked to constant-pressure calorimetry more directly, but the theme of measuring the temperature change in the water is consistent.  For an exothermic reaction, for instance, the temperature of the surrounding water will rise, because the reaction (the system) releases heat energy to its surroundings.  

Depending on the experimental constraints, calculations involving this heat energy transfer then give information about the enthalpy change of the process (𝛥H, or “Delta H,” in constant-pressure calorimetry) or the internal energy change of the process (𝛥U, or “Delta U,” in constant-volume calorimetry, as described here).  Such quantities are typically reported in calories (cal) or joules (J); hence this piece’s title. 

“Return to pursuits epistemic
In classrooms and lab spaces chemic;
The weather is wintry 
For ‘spring’ term re-entry:
Act 2 of the year academic.”  

This blog entry, written at the start of Spring 2021, corresponds to the Twitter limerick posted on 13 January 2020, as last year’s spring term began.  Revisiting it in this space provides an opportunity to set out some general goals for the new year and the new semester, just before spring classes begin.  

“Return to pursuits epistemic / 
In classrooms and lab spaces chemic…”
The vocabulary is lofty in both lines one and two: a “pursuit epistemic” is an endeavor related to learning; a “lab space chemic” is a chemistry laboratory.  Mid-January brings a return to focused spaces such as classrooms and labs, with the start of a new term, after the semester break.  

“The weather is wintry /
For ‘spring’ term re-entry…”          
It is harder to find the motivation to begin a “spring” semester in the height of winter than to begin the “autumn” semester in late summer.  Lines three and four acknowledge this difficulty!  

“Act 2 of the year academic.”
The essay’s title takes its inspiration from this last line of the limerick.  Moreover, while I cannot exactly remember my thought process from last January, I suspect that the rhymes from lines one and two arose from an end goal of “academic,” so that the last line gave the original poem its shape, as well.  

An academic year lends itself well to (my admittedly simplistic understanding of) a two-act dramatic structure: a story told in two parts, separated by a break.  While a music-less entr’acte is a contradiction in terms, writing this poem parallels some of the role of playing or hearing such a composition: providing some time to recenter and readjust to the setting.

Certainly, the second act mentioned here– Spring 2020– brought with it quite a plot twist, which many of these Spring 2021 essays will revisit.  My Twitter posts provided more immediate reactions than did this site’s entries during the same time period, and it will be interesting to reconsider these poems from the perspective of nearly a year onward.