Thermoelectric vapor-pressure osmometry

Abstract

ABSTRACT*The thermoelectric vapor pressure osmometer is established as a satisfactory instrument for the determination of the vapor pressure lowering of solutes in solutions. The calibration constant, a 1 , of the instrument is demonstrated to be independent of the nature of the solute and can be calculated from a knowledge of the system geometry and measurable thermodynamic and transport parameters.Experimental results are evaluated in terms of the change in resistance of the thermistor and the concentration of solution. It is necessary to use a seconddegree equation in concentration plot to fit the data. Evaluation of the coefficient of the second-order term requires the incorporation of a heat-of-mixing term in the form of the Van Laar equation. The concentrationindependent term 8 for the heat of mixing is obtained for fourteen solute-solvent pairs.

Number-Average Molecular Weights of Natural Organic Matter, Hydrophobic Acids, and Transphilic Acids from the Suwannee River, Georgia, as Determined Using Vapor Pressure Osmometry

“…Equation (8) can be solved to obtain M n for a single solution; however, due to data scatter (Adicoff and Murbach, 1967;Meeks and Goldfarb, 1967), a single ''best fit'' value of M n is preferable and was obtained in this study by minimizing the error between h 0 and h 0 CALC within sets of colligative measurements that are obtained over a range of W ORG . Equation (7) naturally yields Equation (9) from which h 0 CALC was determined:…”

Nondestructive vapor pressure osmometry in vacuo

“…Steglich, Hofle, and Vorbmggen (6)(7)(8) have found that 4-dimethylaminopyridine (DMAP) is approximately 104 times more active than pyridine when used as an acylation catalyst. Connors (9) reported applying DMAP to the titrimetric determination of alcohols.…”

Aspects of vapor pressure osmometry

“…where K , is a calibration constant a t the steady state, C is the solution concentration, M , is the number-average molecular weight of the solute, and A2 and A 3 are the second and third virial coefficients of the solute, respectively. Several…”

“…where K , is a calibration constant a t the steady state, C is the solution concentration, M , is the number-average molecular weight of the solute, and A2 and A 3 are the second and third virial coefficients of the solute, respectively. Several attempts have been made to analyze the heat transfer processes taking place in the thermal chamber.lY2 However, it has been found that processes such as heat conduction from the solution drop surface to the ambient vapor and from the solution drop to the thermistor lead wire can O C C U~,~,~ so that true thermodynamic equilibrium between the solution drop and the solvent vapor may not be attained.…”