In an article entitled as above it is proposed that the traditional (nondimensional) definition of [atomic and] molecular weights be altered, so that they would be expressed as dimensional quantities. I disfavor this proposal, and want to point out that there is an alternative to it, which is very simple and completely straightforward. Anyone who does not wish to deal with unitless atomic and molecular weights has the option of multiplying the numbers in question by the SI-derived unit (1 g/mol). The result of this operation is conventionally called "molar mass", M; it is defined by the equation, M = m/n, in which m represents mass, and n the so-called "amount of substance", or "chemical amount" (1). This relationship is general, inasmuch as the definition of the SI mole stipulates that the molar mass of carbon-12 equals exactly 12 g/mol. So, for example, if the molecular weight of a given protein is 50,000, its molar mass equals 50,000 g/mol, and it must consist of molecules, each of which has a mass of 50,000 daltons. By this approach, one can choose whichever description of the system is most convenient and appropriate to the context.

Literature Cited

1. International Union of Pure and Applied Chemistry. Quantities, Units and Symbols in Physical Chemistry, 2nd ed.; Mills, I.; Kallay, N.; Kuchitsu, K.; Cvitas, T.; Homann, K., Compilers; Blackwell: Oxford, 1993; p 41.

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