Chemistry Chat

In the previous chat,¹ I introduced the difficulty of keeping up with the changes in high school chemistry. In this paper, I reluctantly disclose examples of how I am at a loss regarding what to do when students ask me questions that I cannot answer appropriately. If I had sufficient knowledge and experience, I could promptly satisfy the students.

In Japanese high schools, students learn how to measure molecular weight (or formula weight) using the following four methods²:

• Gas equation (Dumas method)
• Elevation of boiling point
• Depression of freezing point
• Osmotic pressure

Students and colleagues often ask this question, but I am at a loss because I do not have any answers. The names of organic compounds that are popular in our daily life often terminate with an [n] pronunciation and have the following suffixes:

• Hydrocarbons: -ane, -ene, -yne
  (e.g., methane, polyethylene, toluene)
• Nitrogen-containing compounds: -in, -ine
  (e.g., glycine, adenine, caffeine)
• Antibiotics: -in
  (e.g., streptomycin, penicillin)

The definition of "amount of substance" was changed in 2019,^6a and we have to change its explanation accordingly. However, an experienced teacher in our school insisted that a conventional explanation would be more understandable to students than the updated one:

(Previous Explanation)^6b
The mole is the amount of substance in a system that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol".
The number of ¹²C atoms in 12 g of carbon 12 was experimentally determined as 6.02...×10²³ /mol, which is called the Avogadro constant, NA. The Avogadro constant and standard of mass (kilogram) were determined independently and contain errors.

(Current Explanation)^6a
One mole contains exactly 6.02214076 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in mol⁻¹.
In other words, we determined that one mole is a collection of exactly 6.02214076 × 10²³ particles. Consequently, the mass of one mole of carbon 12 was revised to 11.9999999958 g.

Even after the change, the mass of one mole of 12C atoms is the same as before, within the range of significant decimal places used in high school chemistry (usually up to three digits). I introduce only the current definition to my students and omit the historical background to avoid confusion and to save class time. We must proceed to the next difficult topic, a stoichiometry calculation. I usually agonize over whether or not I should tell them the history.

Every day I encounter topics that are difficult for a high school teacher to explain, but many topics are probably obvious to experts. From an educational standpoint, it is a good way to entrust questions to students so they can find answers. However, as a chemist, I wish to find answers by myself. At the very least, when I know a thing, to hold that I know it; and when I do not know a thing, to allow that I do not know it.⁷

The topic of molecular polarity was introduced in the previous article.¹ One of the readers pointed out that it was incorrect to judge the polarity of a liquid flowing out of a burette by whether the flow bent when a charged rod was brought close to it. The reader stated that the bending of the water flow was based on a phenomenon called "electrostatic induction," in which water is attracted to charged substances, and is not attributed to the polarity of the molecules. Details are available in reference 8. I express my deep appreciation for this suggestion.

References

1. H. Onuki, TCIMAIL 2024, 196, 16.
2. T. Tatsumi, et al., Ministry of Education, Culture, Sports, Science and Technology Approved Textbook "Chemistry", 2022, Suken Publishing. (Japanese)
3. S. Owen, Chemistry for the IB diploma, Second Edition; Cambridge University Press, 2014; p. 530.
4. National Center for University Entrance Examinations, Common Test for University Admissions in Japan in 2024, “Chemistry” (Japanese) (accessed: September 14, 2024).
5. International Union of Pure and Applied Chemistry, “Nomenclature”, (2013) (accessed: September 6, 2024).
6. (a) R. Marquardt, J. Meija, Z. Mester, M. Towns, R. Weir, R. Davis, J. Stohner, Pure Appl. Chem. 2018, 90, 175. (accessed: September 9, 2024); (b) Bureau International des Poids et Mesures, The International System of Units (SI) 9th edition, 2019.
7. The Analects of Confucius, Weizeng No. 2, 17.
8. M. Ziaei-Moayyed, E. Goodman, P. Williams, J. Chem. Educ. 2000, 77, 1520.