Specific volume

Abstract: Redefinitions of the kilogram based on either the electron mass, the carbon-12 atomic mass or a pseudo-mass proportional to the Planck constant are examined, together with respective resulting uncertainties in a number of important constants. The kilogram-to-dalton mass ratio is shown to play a central role in coupling mass unit definitions with those of units for amount of substance, since the kg/Da mass ratio is equal to the kilomole-to-entity amount-of-substance ratio in a compatible formulation. Because of this coupling, a redefinition of the unit for amount of substance using a fixed exact value of the kmol/ent ratio implies an exact value of the dalton in terms of the kilogram (regardless of how the kilogram itself is defined), thereby eliminating any need for a 'correction factor' in expressions involving amount-specific mass. In particular, compatible definitions guarantee that NA Da = Da ent−1 = kg kmol−1 = g mol−1, exactly.