Raoult's law revisited: accurately predicting equilibrium relative humidity points for humidity control experiments

TL;DR

This paper introduces a new humidity control device to accurately measure equilibrium relative humidity for biological crystallization, revisiting Raoult's law with extended statistical mechanics arguments.

Contribution

It provides a novel experimental setup for precise humidity measurements and extends Raoult's law to solutions with molecules of different sizes.

Findings

Accurate humidity measurements for crystallization precipitants.

Validation of Raoult's law extension for unequal molecule sizes.

Enhanced understanding of solvent vapor pressure in biological solutions.

Abstract

The equilibrium relative humidity values for a number of the most commonly used precipitants in biological macromolecule crystallisation have been measured using a new humidity control device. A simple argument in statistical mechanics demonstrates that the saturated vapour pressure of a solvent is proportional to its mole fraction in an ideal solution (Raoult's Law). The same argument can be extended to the case where solvent and solute molecules are of different size.