User:WilfriedC/Playground/Girolami method

The Girolami method is a predictive method for estimating densities of pure liquid components at room temperature. The objective of this method is the simple prediction of the density and not the high precision.

Procedure
The method uses purely additive volume contributions for single atoms and additional correction factors for components with special functional groups which cause a volume contraction and therefore a higher density. The Girolami method can be described as a mixture of an atom and group contribution method.

Atom contributions
The method uses the following contributions for the different atoms:

A scaled molecular volume is calculated by

$$V_S \,=\, \sum_i V_i$$

and the density is derived by

$$d \,=\, \frac{M}{5 \cdot V_S}$$

with the molecular weight M. The scaling factor 5 is used to obtain the density in g·cm-3.

Group contribution
For some components Girolami found smaller volumes and higher densities than calculated solely by the atom contributions. For components with it is sufficient to add 10 % to the density obtained by the main equation. For sulfone groups it is necessary to use this factor twice (20 %).
 * a hydroxylic function (Alcohols)
 * a carboxylic function (Carboxylic acids)
 * a primary or secondary amine function
 * an amide group (incl. amides substituted at the nitrogen)
 * a sulfoxide group
 * a sulfone group
 * a ring (non-condensed)

Another specific case are condensed ring systems like Naphthalene. The density has to increased by 7.5 % for every ring; for Naphthalene the resulting factor would be 15 %.

If multiple corrections are needed their factors have to be added but not over 130 % in total.

Quality
The author has given a mean quadratic error (RMS) of 0.049 g·cm-3 for 166 checked components. Only for two components (Acetonitrile und Dibromochloromethane) an error greater than 0.1 g·cm -3 has been found.

External link

 * Online calculator for the Girolami model