kow - Chapter 7 Organic Liquid-Water Partitioning Klw and...

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Chapter 7 Organic Liquid-Water Partitioning K lw and K ow
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Air Water Octanol A gas is a gas is a gas T, P Fresh, salt, ground, pore T, salinity NOM, biological lipids, other solvents Pure Phase (l) or (s) Ideal behavior P o L C sat w C sat o K H = P o L /C sat w K oa K H K ow = C sat o /C sat w K ow K oa = C sat o /P o L
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Equilibrium partitioning between water and any organic liquid: il iw iw il ilw x x K γ = = ' prime refers to mole fraction basis better to use molar concentration note how this equilibrium constant is related to those discussed previously il iw l w iw il ilw V V C C K = = ial iaw ilw K K K = phase change costs cancel small? large?
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Effect of salinity on water:organic liquid partitioning Salinity will increase tendency to partition into the organic phase by decreasing the solubility (increasing the activity coefficient) of the solute in water. Assuming that salts are largely insoluble in the organic phase. Account for salinity effects via Setschenow constant: tot s i salt K ilw salt ilw K K ] [ , 10 + =
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Effect of Temperature on water:organic partitioning cst RT H K i lw ilw + - = ln As per previous discussions, assume enthalpy change of the partitioning process is constant over the relevant range of T E iw E il i lw H H H - = Total enthalpy change = different between excess enthalpy of solubilization in water and solvent solvent Pure liquid water H E iw lw H H E il
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Temperature dependence of K lw • Typically H E iw and H E il are similar in magnitude, so the temperature dependence of K lw is small (negligible) not true when there is great dissimilarity between solute and solvent, i.e. PCBs, PAHs in water, ethanol in nonpolar solvent As usual, correct for temperature (when necessary) via: cst RT H K i lw ilw + - = ln
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Comparing different organic solvent- water systems Recall that partitioning will be driven by vdW forces polarity/polarizability H bonding The better the match between chemical properties of solute and solvent, the higher the equilibrium constant for example, better extraction solvent
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LFERs for relating different organic solvent- water systems IF the two solvents are similar, then simple linear FER can be
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kow - Chapter 7 Organic Liquid-Water Partitioning Klw and...

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