Density and Molecular Volume

The movement of molecules through a fluid depends on the size, shape and mass of the molecules, as well as on the physical properties of the surrounding solvent. Aqueous solutions of proteins, nucleic acids or carbohydrates are generally more dense than pure water under the same conditions. The macromolecules themselves act as if they were denser than water, and this is the basis for various ultracentrifuge techniques described in this section. 

An equivalent expression, using the mass of each component, g, (in grams), defines the partial specific volume, v,  

The density, or mass per unit volume, p, of a mixture is given by  

Parliai rnolal volumes and partial specific volumes are specific examples of a mucli more general Iheimodynamic rule thatextensivfe properties lor any system at equilibrium can always be expressed in terms of surris of the, partial molal (or partial specific) quantities of each of the individual,1 components in the nix ufe  

Note that the total volume is not (necessarily) the sum of the volumes of the two separate (pure) components. This can be for several reasons. 

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Girolami, G. S., A Simple Back of the Envelope Method for Estimating the Densities and Molecular Volumes of Liquids and Solids. J. Chem. Educ., 1994 71, 962-964. 

In the following table are given the densities and molecular volumes of the salts —7... 

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