Dispense With The Mole

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