What the MOLE?

mole definition

What is your definition of the term “mole” in chemistry? Many articles have been written about the term and the confusion surrounding it. It was not considered an SI unit (with an IUPAC definition) until 1971 (Fang, Hart, Clarke). Textbooks had included their own definitions prior to the IUPAC definition, so when IUPAC offered their definition in 1971, there was little change noticed by chemistry teachers. Those textbook definitions vary as much as the definitions that teachers provide when asked. (Giunta) IUPAC is considering a change to the 1971 definition (most recently in Korea this past week), but it will likely not be a significant change for most chemistry teachers. There has been discussion about whether the SI definition of the mole as determined by IUPAC necessarily needs to be identical to the definition used by chemists and teachers. Carmen Giunta discusses the proposed change in her recent JCE commentary “The Mole and Amount of Substance in Chemistry and Education: Beyond Official Definitions”.  (Commentaries are freely available without a JCE subscription.)

Many articles note the mole as being a topic that is wracked with misconceptions. Novick and Menis offer a few generalized misconceptions that they have recognized:

  • Few students recognize the MOLE as a counting unit (students recognize the mass relationship, but not the number of items). 
  • The mole is restricted to a specific number of GAS particles (related to Avogadro’s hypothesis), but not liquid or solid particles. 
  • Students often think the mole is a property of a molecule.

Fang, Hart and Clarke suggest that teachers begin their exploration of the mole by considering the ratios involved, then discuss the application of the mole in terms of relative atomic mass while avoiding the number, 6.02 x 1023 until students have a basic conceptual grasp of the term.

I have read several articles concerning the “mole” recently. I have highlighted a few below (many of which are briefly referred to above). This is not an all-inclusive list, but a small sample of some that I have found especially useful as I explored the issue.

Su-Chi Fang, Christina Hart, and David Clarke, Journal of Chemical Education 2014 91 (3), 351-356, DOI: 10.1021/ed400128x
Andrzej Barański, Journal of Chemical Education 2014 91 (8), 1098-1098, DOI: 10.1021/ed5002398
,Su-Chi Fang, Christina Hart, and David Clarke, Journal of Chemical Education 2014 91 (8), 1099-1100, DOI: 10.1021/ed500424s
S. Novick and J. Menis, Journal of Chemical Education 1976 53 (11), 720, DOI: 10.1021/ed053p720 (Discusses some misconceptions surrounding the mole.)
Josefina Arce de Sanabia, Journal of Chemical Education 1993 70 (3), 233, DOI: 10.1021/ed070p233 (Includes an excellent activity to use as an introduction to understanding the ratios involved in the connection between the mole, number of particles and mass.)
Carmen J. Giunta, Journal of Chemical Education Article ASAP, DOI: 10.1021/ed5007376