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Environment

Dispense With The Mole

October 6, 2014 | APPEARED IN VOLUME 92, ISSUE 40

Regarding the ACS Comment “Check Your IQ on the SI”: In theory, we can dispense with the mole (C&EN, Aug. 4, page 32). The mole, molarity, and molality were adopted as convenient ways to express relative amounts and concentrations of substances when we didn’t know the actual mass of atoms and molecules—when the very existence of atoms and molecules was in dispute.

Now we know, which has enabled us to come up with the number 6.022 × 1023, give or take, and requires us to explain to students—who question why anyone would specify such a ridiculous number— that it wasn’t chosen but is experimentally derived. Now that we know the actual mass of atoms, ions, and molecules, we can describe the actual number of entities directly—for example, an acid as 1.5 YH+ per liter (Y = yotta = 1024), which is about 2.5 mol H+/L. We could rid ourselves of an unnecessary and confusing-to-beginners concept, but of course it will never happen.

Howard J. Wilk
Philadelphia

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Comments
Juan Ramón González Álvarez (February 3, 2017 1:54 PM)
I am a chemist and I am still trying to understand why SI prefixes are not used by chemists.

I am familiar with all the SI prefixes, but even if I was not familiar, I would prefer to learn a pair of universal prefixes rather than deal with the mole and all the issues, inconsistencies, and headaches it brings to us:

** I have to learn SI prefixes the same. I.e. the mole is redundant.

** I have to learn two mole concepts: the chemical mole and the thermodynamic mole [1].

** I have to learn three definitions of mole in the SI. The original definition in the SI (1971), the amended definition (1980), and the new definition proposed for the future SI [2]. I have to learn the differences and check what one is being used in a given reference. For instance, the definition of mole in the current SI gives a uncertainty to the Avogadro constant, the proposal for the new SI sets a exact value for this constant and moves the uncertainty to M(¹²C).

** Then I have to deal with "correction factors" to compensate for the incompatibility between the redefinitions of mole and kilogram [3].

** I have to learn an abstruse name for the physical quantity that supposedly is measured in moles, "amount of substance", like if a mol of electrons is a substance. And then I have to deal with the proposals to change that physical quantity to "chemical amount", "stoichiometric amount", or "enplethy" [2].

** I have to deal with the ontological confusion between counting and measuring [4].

** I have to deal with redundant equations such as pV=nRT and pV=NkBT.


REFERENCES:

[1] Failures of the global measurement system. Part 1: the case of chemistry. Gary Price. Accred Qual Assur (2010) 15:421–427.

[2] What is a Mole? Old Concepts and New. Jack Lorimer. In CHEMISTRY International January-February 2010.

[3] Comments on recent proposals for redefining the mole and kilogram. B. P. Leonard. Metrologia 47 (2010) L5–L8.

[4] The Mole is Not an Ordinary Measurement Unit. Ingvar Johansson Accred Qual Assur (2011) 16:467–470.

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