The Henry's Law Constants of the Haloacetic Acids |
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| Authors: | D J Bowden S L Clegg P Brimblecombe |
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| Institution: | (1) School of Environmental Sciences, University of East Anglia, Norwich, NR4, 7TJ, U.K. |
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| Abstract: | Henry's law constants K H (mol kg-1 atm-1) have been measured between 278.15 K and 308.15 K for the following organic acids: CH2FCOOH (ln(KH298.15 K]) = 11.3 ± 0.2), CH2ClCOOH (11.59 ± 0.14), CH2BrCOOH (11.94 ± 0.21), CHF2COOH (10.32 ± 0.10), CHCl2COOH (11.69 ± 0.11), CHBr2COOH (12.33 ± 0.29), CBr3COOH (12.61 ± 0.21), and CClF2COOH (10.11 ± 0.12). The variation of KH with temperature was determined for all acids except CH2FCOOH and CBr3COOH, with  r H° for the dissolution reaction ranging from –85.2 ± 2.6 to –57.1 ± 2.5 kJ mol-1, meaning that their solubility is generally more sensitive to temperature than is the case for the simple carboxylic acids. The Henry's law constants show consistent trends with halogen substitution and, together with their high solubility compared to the parent (acetic) acid (ln(KH298.15 K]) = 8.61), present a severe test of current predictive models based upon molecular structure. The solubility of haloacetic acids and strong dissociation at normal pH mean that they will partition almost entirely into cloud and fog in the atmosphere (0.05–1.0 g H2O m-3), but can reside in both phases for the liquid water contents typical of aerosols (10-5-10-4 g H2O m-3). |
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| Keywords: | Henry's law solubility aerosol fluoroacetic acid chloroacetic acid bromoacetic acid difluoroacetic acid dichloroacetic acid dibromoacetic acid trifluoroacetic acid trichloroacetic acid tribromoacetic acid chloro-difluoroacetic acid |
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