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Saturated Salt Solutions

The relationship between water activity (aw) and temperature of saturated salt solutions generally follows the following empirical model:

    ln(aw) = k1/T - k2

where:
k1 and k2 are constants, different for each salt
T is temperature in Kelvin

Constants k1 and k2 may be calculated by regression analysis of experimental data. The following table gives the values for a range of salts based on experimental data previously published by Dr Labuza.

Salt k1 k2 Mean relative % error Water Activity at 25C
LiBr 620.636 4.8327 0.1574 0.064
ZnBr2 409.626 3.9159 1.2005 0.078
KOH 2094.49 9.4977 1.8022 0.082
LiCl 10.8233 2.2193 0.204 0.113
LiI 982.733 5.0477 0.9218 0.176
K2C2H3OH 333.9 2.6185 1.1647 0.225
MgCl2 151.065 1.6271 0.4059 0.328
NaI 643.011 3.1407 1.4864 0.382
K2CO3 -3.024 0.83 0.0046 0.432
Mg(NO3)2 484.699 2.267 0.3413 0.529
NaBr 447.805 2.0575 0.318 0.576
KI 258.155 1.2388 0.0095 0.689
NaNO3 253.38 1.1493 0.1487 0.743
NaCl 23.1092 0.3607 0.1631 0.755
KBr 171.275 0.7828 0.3117 0.809
(NH4)2SO4 76.8191 0.469 0.0337 0.810
KCl 157.059 0.6967 0.0289 0.843
K2NO3 192.089 0.7183 0.6177 0.936
K2SO4 52.7544 0.2046 0.0223 0.973

A zip file of an Excel spreadsheet showing the raw data and predicted aw values based on the model may be downloaded:
click here to download

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Last modified: 10-Aug-2008