*“With Avogadro’s number–**And a molar mass to boot–**We can practice stoichiometry**And many calcs compute! **(If using six times ten**Raised to the power twenty-third,**Be sure to check your answers**So their scale is not absurd!)”*

The Twitter poem posted on 23 October 2019 can be viewed as a STEM education-themed poem; it is written in a “teacher’s voice” and examines a chemistry-specific metacognitive technique.

**“With Avogadro’s number– /****And a molar mass to boot– /****We can practice stoichiometry /****And many calcs compute!”**

The first four lines specifically were posted on Twitter during National Chemistry Week 2019. “Avogadro’s number” is named in honor of Amedeo Avogadro, who has been cited in this space before regarding his gas law, which related the amount of a gas to its volume. The SI unit for amount is the mole. Chemists use Avogadro’s number to convert between moles of a substance and the number of atoms or molecules of that substance. A useful and common analogy is the concept of a dozen. Saying someone has a dozen eggs is equivalent to saying someone has twelve eggs. Saying someone has one mole of eggs is equivalent to saying someone has 6.022 x 10^{23 }eggs. Given its magnitude, Avogadro’s number is useful in converting between the particulate scale and the macroscopic scale.

The concept of molar mass relates moles to the more familiar unit of grams. The number underneath an element’s chemical symbol on the periodic table is its molar mass: the number of grams in one mole of the element. For example, measuring out 12.01 grams of carbon is equivalent to measuring out one mole of carbon, which is equivalent to measuring out 6.022 x 10^{23 }atoms of carbon. Mastering these concepts opens the door to a wide array of interesting calculations, collectively termed stoichiometry.

“**(If using six times ten /****Raised to the power twenty-third, /****Be sure to check your answers /****So their scale is not absurd!)”**

I refrained from posting these final four lines on Twitter last fall since, without additional context, the second set of rhymes could sound critical. As alluded to above, though, this is a common refrain in my classroom, whenever Avogadro’s number (“six times ten raised to the power twenty-third,” poetically) is involved. I remind students that as they are converting between grams, moles, and numbers of atoms, the scales of the numbers will be very different. (For instance, a 10.00 gram sample of carbon is equivalent to 0.8326 moles of carbon, a quantity which is equivalent to 5.014 x 10^{23} atoms of carbon.) A student can always use common sense and these very different scales to double-check that they’ve not reported an incorrect answer where the scale is accidentally “absurd”: they can think about their thinking, via a chemistry-specific metacognitive technique.