X-Message-Number: 17940
Date: Thu, 15 Nov 2001 09:13:45 -0800 (PST)
From: Doug Skrecky <>
Subject: freezing point depression theory

  Correction for solute/solvent interaction extends accurate
  freezing point depression
  theory to high concentration range.
  Journal of Biochemical & Biophysical Methods.  29(3-4):217-35, 1994 Dec.
  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 Mwc is the
  mass of water in solution Mw 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 the experimental plot of Mw/M(s) as a function of 1/delta T (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 point depression
  (+/- 0.05 degrees 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 negligible below this
  limit. This is contrary to the view of many authors due to the common
  practice of including hydration forces (a soft potential added to the hard
  core atomic potential) in the interaction potential between solute particles.
  When this is recognized the two viewpoints are in fundamental agreement.

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