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Solubility book (3rd Edn)
Harina A. Raja
To find the solubility of benzoic acid in absolute ethanol using their density measurements
Make a saturated solution of benzoic acid and ethanol in a 5 ml volumetric flask. Heat it for about 5 minutes in a thermostat water bath at 40C. Remove the volumetric flask and collect the supernatant and fill up the vial to about 1ml of the supernatant and label it as sample 1, 2, 3,4 and 5. Repeat the process at reular intervals of time such that the interval oftime between each of the samples 2,3,4, and 5 is exactly 6 minutes.
[plot the solubility vs time JCB]
Sample 6 was collected but since its volume was less than 1ml it was discarded. It is important to have the volumes and time intervals consistent in this procedure. The mass of the samples were increasing from samples 2,3,4 as the time increased but started decreasing for sample 5. If more samples were collected we could have been able to see a much more significant pattern. The reported solubilities ranged from 2.43 M to 2.72 M. (
). The observed values ranged M from 2.1902 M to 2.6999 suggesting that there's a consistency in the observed solubilities as the average falls within the previously reported ranges of concentration.
[How do your numbers compare to the reported solubility of benzoic acid in ethanol? JCB]
[In the future you should have at least one sample with a known concentration - around 1M - to check the density calculation JCB]
The solubility of benzoic acid in ethanol is was determined in the range of 2.1902 M to 2.6999 M. Since there was not any solid settling in the bottom of the vials after all samples were collected, it can be concluded that the solution was not supersaturated.
[Do you think you should include the 2.19M value? JCB]
12:06- Solute was added to the solution in an attempt to make it super saturated and the mixture was agitated to eradicate any lumps and completely dissolve.
12:09- Approximately 1ml of sample 1 was collected.
12:27 - Placed the solution in the thermostat water bath at 40C.
12:33- Took out the solution from thermostat water bath at 40C.
12:35- Sample 2 was collected and placed the solution back in the thermostat water bath.
12:36- Sample 2 was placed in room temperature water bath.
12:41- Took out the solution from thermostat water bath.
12:42- Sample 3 was collected and placed in room temperature water bath.The solution was placed back in the thermostat water bath.
12:46- Sample 2 was sonicated for about a minute to prevent supersaturation
12:48- Took out the solution from thermostat water bath.
12:49- Sample 4 was collected and placed in room temperature water bath which was at 25.5C.The solution was placed back in the thermostat water bath.
12:55- Took out the solution from thermostat water bath.
12:57- Sample 5 was collected. Mass of sample 2 solution was found to be 0.8870g.
12:59- Sample 5 was placed in room temperature water bath.The solution was placed back in the thermostat water bath.
13:05- Took out the solution from the thermostat water bath and the mass of samples 3,4 and 5 were recorded as 0.8902g, 0.9016g and 0.8917g respectively. The volumes of all samples were roughly 1ml as a 1ml volumetric flask was used to collect the samples.
[What did you use to measure the volume of the weighed samples - do you really mean "roughly 1 ml"? JCB]
[What density did you get for the pure solvent? JCB]
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