Marilyn Chau and David Bulger


Determine the solubility of benzoic acid in ethanol by gravimetric analysis.


Make saturated solution of benzoic acid in ethanol, heat to 30dC in water bath, centrifuge, evaporate the supernatant liquid, and weigh the benzoic acid. Determine solubility by comparing the evaporated benzoic acid with the total supernatant volume before evaporation.




Some of the solvent may have evaporated during the transfer and the pipet might not have transferred as much solvent due to vapor pressure. This was expected to give a solubility reading slightly less than the literature. The solubility was determined to be 2.67 M, [Why is this number different from the calculated one in the spreadsheet? JCB] which is greater than the mean ONS results as of 02/08/10 (2.55 M) [There was an outlier from an old paper skewing this and is now marked DONOTUSE- the average is now 2.55M JCB] and less than the literature value of 2.72 M.


The solubility of benzoic acid in ethanol was determined to be 2.67 M. [Great job for a first experiment! Looks like you addressed the key issues and have a good record JCB] [Agreed AL]



15:51 Placed 250 mL beaker filled with 200 mL water on a hot plate with spin bar and heated to 30dC as measured with a thermometer
15:55 Weighed glass centrifuge tube (13.847 g)
16:08 Added 2 mL 95% ethanol by Eppendorf pipet to the centrifuge tube (15.395 g)
16.29 Added benzoic acid (16.690 g)
16:30 Placed centrifuge tube in hot water bath (25dC in water bath) [Is it possible to take a picture of your setup in the future? That is often quicker than having to explain in detail JCB]
16:51 Removed centrifuge tube (30dC)[This might not be hot or long enough - you should go to 40C for a few hours JCB]
16:53 Inserted in centrifuge [You should equilibrate at 25C for at least an hour then sonicate or shake vigorously to avoid supersaturation before the centrifuge JCB]
17:03 Removed from centrifuge
17:08 Weighed Erlenmeyer flask (13.933 g) Note: Was not tarred correctly; please disregard this measurement.
17:11 Shook centrifuge tube
17:13 Centrifuged
17:18 Removed from centrifuge
17:19 Added 0.5 mL of supernatant by Eppendorf pipet to Erlenmeyer flask (40.354 g) [What is the precision of the pipette? JCB] [Since these types of pipettes are not designed to handle non-aqueous liquids - you should weigh out the same volume of pure ethanol and compare the calculated with the known density. A much better solution is to use a 0.5 or 1.0 mL volumetric flask JCB] The pipet had a standard deviation of 0.003 5 and a percent error of 0.55%.

17:24 Weighed new Erlenmeyer flask (40.141 g)
17:25 Added 0.5 mL of supernatant to second Erlenmeyer flask previously labeled "3" (40.581 g)
Left to evaporate over the weekend.


15:28 Weighed evaporated crystals in flask (40.304 g) (ONSCExp160_001, ONSCExp160_002)
16:17 Determined precision of Eppendorf pipet (refer to spreadsheet for calculations).


Solubility of Benzoic Acid in Ethanol.
Seidell, Atherton. Solubilities of inorganic and organic compounds. Vol. 2, pp. 136.
Sublette, Marcus. ONSCExp055
Vallejo, Pedro. ONSCExp054