The authors reply to Gorin.
While agreeing with the reasoning expressed in the letter by George Gorin, we would like to underline the following points. His starting point is that "the numbers in question" are to be multiplied by 1 g/mol in order to obtain the molar mass or mass of a mole, and by 1 dalton/molecule to obtain the mass (in daltons) of a molecule: it is clear that the "numbers in question" are the molecular weights expressed as pure numbers.
By contrast, we discussed the possibility of expressing molecular weights either by pure numbers, or by the dalton unit (according to a more general way of expressing quantities) (1). Adopting the second point of view, the molar mass M is given by
The two points of view are equally tenable because they stress different requirements: (i) the approach of the SI system whereby a single unit of measurement is recommended (e.g. the gram rather than the dalton for mass); (ii) the principle of giving to each quantity a dimensional unit of measure (unless the quantity is essentially relative, as for example in the case of absorbance).
Literature Cited
- Paolini, M.; Cercignani, G.; Bauer, C. J. Chem. Educ. 2000, 77, 1438-1439.
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