Water Osmosis

A brief overview of the origin and formulations of past equations that were originally based on the gas laws to estimate osmotic pressures is presented.  These original formulas are not capable of estimating the contribution to osmotic potential of an individual solute component, either an inorganic or an organic compound of a mixture of solutes in water solution. Further, unlike the authors’ newly developed equation, past equations for estimating osmotic potentials, are dependent on coefficients and only reasonably accurate for low solution concentration and temperature conditions.

This site follows with the development of the initial formulation and the progressive improvement of the authors’ equation to calculate the osmotic potentials of the solutes in aqueous solutions without the use of coefficients. The calculations are compared with recorded osmotic potential data made by past authors. Additionally, examples on how it has already been applied successfully to help elucidate several interesting biological and physical phenomena are presented. It concludes with a detailed review of the final modification of their equation to enable the calculation of osmotic potentials for aqueous solutions of inorganic and inorganic over very wide solute concentration and temperatures levels.

The approach for the development of a new coefficent-less equation for calculating the osmotic potential of aqueous solutions.

 A new different approach to calculating osmotic potential, based on a dynamic model of the structure of water, was developed by Cochrane (1983, 1984), in terms of acceptable physical principles. -It is interesting to note that Cochrane’s 1983 publication was originally reviewed by the American Society of  Physics, who passed it on to Medical Physics for publication, because of its importance to medicine. The equation developed enabled empiri­cally accurate calculations of the contribution to osmotic potential of the separate solutes of water solutions over moderate concentration ranges without the use of coeffi­cients. As time passed, that earlier equation was revised to show that improved equations could be developed from the conceptual model upon which it is based; fur­thermore, that the final improved equation would give very accurate predictions of osmotic potentials over wide ranges of both electrolyte and non-electrolyte solute concentrations and temperatures.

    The new coefficientless equation developed for calculating osmotic potentials of aqueous solutions, was based on a molecular model of water movement at and across a semipermeable membrane. Its formulation involved no sub-equations that cannot be fully derived from established physical principles. The initial equation was first tested by calculating the osmotic potentials of a series of aqueous NaCI solutions with concentrations ranging from 0.l03 to 4.382 kmol m^-3, and comparing those calculations with calculations made using equations based on coefficients recorded in the literature. Virtually the same results were obtained. Subsequently, it was improved and tested successfully by comparative calculations on a selection of inorganic and organic aqueous solutions. The principles it embodies provide for the visualization of the molecular role of water as a unifying mechanism. Factors that affect the size of the structure of water, and the conse­quent distance an individual molecule must travel to and fro across its “cage” of space, determine direction and rate of flow. It is evident that the equation will provide a new research tool for many osmotic-potential-related ques­tions in medicinal, biological, agricultural, earth and physical sciences.