Get Your BA in Solubility

After grading this year’s Open Notebook Science solubility challenge lab reports I decided to look into solubility reporting a little deeper. My representative compound was benzoic acid (BA). I figured there might be a range of reported values on solubilities like there is for melting points. To my surprise, there was not much variation in water solubility information for BA. Most of the BA water solubility information on the internet seems to originate from the Merck Index. The Merck (12th ed) reports the solubility of benzoic acid is 2.9 g/l at 20o C and 3.4 g/l at 25o C. Wikipedia converts the Merck data into 0.34 g/100ml (25 °C). Elsewhere BA’s solubility in water is reported as 2.9% at 20 o C. So the units do vary slightly but mass/volume is favored over molarity (moles/liter) or molality (moles/kg). It is also import to note that temperature must be specified since solubilities may vary significantly by temperature. I did locate one “alternative” benzoic acid solubility – 1 G/300 ml water cited from [Osol, A. (ed.). Remington's Pharmaceutical Sciences. 16th ed. Easton, Pennsylvania: Mack Publishing Co., 1980.1172].

The Merck reports the water solubility of benzoic acid at no less than 12 different temperatures! Amanda Oliveira’s 2007 article in the  Journal of Chemical Engineering reports the solubilities of BA at 8 different temperatures (30.56 – 70.00 oC) measured by titrating aliquots of saturated solution with 0.1 M NaOH. Here the solubilities are reported as molalities. A similar analysis was done by Alexander Apelblat and reported in the 2006 Journal of Chemical Thermodynamics. A graph Merck, Oliveira, and Apelblat is included. The values are similar but not exact. Especially, the Oliveira paper traces an almost straight line where Merck and Apelblat’s lines are curved.


One Comment

  1. Posted February 6, 2011 at 1:09 pm | Permalink

    Brent – we have collected 31 measurements for the solubility of benzoic acid in water:

    I recently posted an analysis of the variability of chemical properties from various sources. As you can see there some of the aqueous solubility data were in large disagreement.

    Would you like to add your results to our ChemInfo Validation sheet on an ongoing basis?

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