Non-ideality in the fluid phase

The dependence of y on pressure is small if the compressibility of liquids is small over the ranges considered. Temperature dependence is usually assumed to have the most significant effect and the effects of pressure are neglected. This assumption enables workers to investigate the effects of temperature and composition on a system of interest from experimental results derived at lower pressure. There is little information available to assess the error propagated by the assumption of pressure independence in high-pressure systems. 

Henry s law (Eqn. 2) can be rearranged to consider the mole fraction solubility of i in pure water, where Yi 1, and the mole fraction solubility of i in a saline solution at the same partial pressure, respectively, enabling the Setschenow equation to be rearranged with respect to the mole fraction solubilities 

This satisfies the condition that as C 0, yi 1. If ki (T) is negative this results in Yi 1, increasing the solubility of i. If ki (T) is positive, this results in yi 1, reducing the solubility of i. Although these effects are commonly called salting in and salting out of the non electrolyte, from Equation (10) it can be seen that these are no more than empirically derived changes in the activity of the dissolved gas. 

Measurements of noble gas solubilty in water and NaCl solutions have focused on low temperatures (0-40°C) and salinities up to that of seawater (Weiss 1970, 1971 Clever 1979a,b). This data is used in noble gas paleotemperature investigations and is 

Although the work of Smith and Kennedy only investigates the effect of NaCl on noble gas solubility, they note that the contribution by individual ions should be additive and in dilute brines it should be possible to estimate the salt effect of multi-electrolyte solutions. While no data exists for Mg and Ca ions, data for KI solutions show that kAr is independent of the electrolyte species (Ben-Naim and Egel-Thal 1965), suggesting that an NaCl equivalent concentration provides a reasonable value from which to calculate the Setchenow coefficient. This relationship has been used in multi-ion mixtures such as seawater and for more concentrated solutions such as the Dead Sea brines (Weiss 1970 Weiss and Price 1989). 

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