text: Membrane osmometry can be used to find one form of this quantity in a polymer, and the distribution of this quantity in a polymer solution is described by the polydispersity index.
full_question: Membrane osmometry can be used to find one form of this quantity in a polymer, and the distribution of this quantity in a polymer solution is described by the polydispersity index. Jean-Baptiste Dumas heated volatile organic substances to determine their vapor densities were proportional to this value. For an ideal gas, this value is equal to RT times density over pressure. The unit defining this quantity is defined as one twelfth the mass of a carbon-12 atom, and is the dalton. For water this quantity is approximately 18 amu ["a-m-u"]. For 10 points, name this quantity that can be found by adding up the individual atomic masses of a compound.
first_sentence: Membrane osmometry can be used to find one form of this quantity in a polymer, and the distribution of this quantity in a polymer solution is described by the polydispersity index.
raw_answer: molecular weight [or molar mass; prompt on "weight" or "mass"]