Correction for solute/solvent interaction extends accurate freezing point depression theory to high concentration range

The authors describe empirical corrections to ideally dilute expressions for freezing point depression of aqueous solutions to arrive at new expressions accurate up to three molal concentration. The method assumes non-ideality is due primarily to solute/solvent interactions such that the correct free water mass M w c is the mass of water in solution M w minus I· M s where M s is the mass of solute and I an empirical solute/solvent interaction coefficient. The interaction coefficient is easily derived from the constant in the linear regression fit to experimental plot of M w M s as a function of 1/ΔT (inverse freezing point depression). The I-value, when substituted into the new thermodynamic expressions derived from the assumption of equivalent activity of water in solution and ice, provides accurate predictions of freezing ppoint depression (±0.05°C) up to 2.5. molal concentration for all the test molecules evaluated; glucose, sucrose, glycerol and ethylene glycol. The concentration limit is the approximate monolayer water coverage limit for the solutes which suggests that direct solute/solute interactions are nergligible below this limit. This is contrary to the view of many authors due to the common practice of including hydration forces (a potential added to the hard core atomic potential) in the interactions potential between solute particles. When this is recognized the two viewpoints are in fundamental agreement.