Researcher

Anthony Shorrock

Objective

To determine the solubility of benzoic acid in methanol.
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Benzoic Acid


Procedure

Six solutions of benzoic acid were prepared in methanol. Each vial was vortexed and heated in a water bath until all mixtures had dissolved completely. Once dissolved, the temperature of the water bath was decreased until the benzoic acid had precipitated back out of the methanol. The temperature was noted for each vial that contained precipitate in order to make a temperature curve.[The procedure section does not have to have all the details of the numbers - it should just be a brief summary of the approach JCB]

Results

Once the six mixtures had been made, they were vortexed until the bezoic acid had completely dissolved into the methanol. The only vials that were unable to do so at room temperature were vials #1 and #3. Vial #3 had to be heated in the water bath to 61 degrees C in order for benzoic acid to completely dissolve. Since this was so close to the boiling point of methanol, 64 degrees C, Vial #3 had to be aborted, while Vial #1 was able to dissolve completely at 58 degrees C. However, after leaving the all the vials, except for #3, out of the water bath overnight at room temperature, they were all able to completely dissolve without the aid of the hot water bath, including Vial #1. Starting the water bath at 25 degrees C and decreasing the temperature about every 5 minutes, the only vial the showed precipitate was Vial #1, which occured at 5 degrees C. The remaining vials were left in the water bath until the temperature had reached -20 degrees C, at which point it was advised to stop the experiment. None of the remaining vials showed precipitate.
Spreadsheet

Discussion

Only one of the six vials containing different concentrations of benzoic acid in methanol demonstrated precipitation. Since only one point was able to be taken from the experiment, a temperature curve cannot be made. A proper temperature curve needs a minimum of three points. Maybe if the mixtures were able to be placed in a colder water bath, the remaining vials would have demonstrated precipitate. All of the samples were disposed of before an NMR could be taken.

[Based on the known solubility of benzoic acid (assuming that is the solute you used) in methanol is it expected that none of your samples came out at -20C? JCB]
[Take an NMR to confirm at least one of those concentrations JCB]
[Something very strange happened in your experiment since your numbers are way off what is expected - the NMR will give us more information about what might have gone wrong JCB]

Conclusion.

No conclusion can be made in this temperature study because a temperature curve cannot be made using only one point.[You don't need a full solubility curve from the data points in this experiment to arrive at a conclusion - answer the questions that you can answer in the discussion and propose a next experiment based on what you find JCB]

Log


2009-06-30
17:30 - Labeled [spelling JCB] 6 half-dram vials #: 1-6.
17:45 - Add copper [spelling JCB] wire tags to all 6 vials.
17:50 - Weighed 1.0027 grams of methanol and 0.8173 grams of benzoic acid, which were both added to vial [spelling JCB] #1.
17:57 - Weighed 1.0621 grams of methanol and 0.4388 grams of benzoic acid, which were both added to vial #2.
18:05 - Weighed 0.9660 grams of methanol and 1.0751 grams of benzoic acid, which were both added to vial #3.
18:12 - Weighed 1.0920 grams of methanol and 0.3209 grams of benzoic acid, which were both added to vial #4.
18:20 - Weighed 1.0879 grams of methanol and 0.2361 grams of benzoic acid, which were both added to vial #5.
18:30 - Weighed 1.0761 grams of methanol and 0.1643 grams of benzoic acid, which were both added to vial #6.[Link to the spreadsheet you used for these calculations in the results section JCB]
18:45 - Observed each vial to see which still contained benzoic acid precipitate at room temperature, 25 degrees C.
18:50 - Vials #1 and #3 were vortexed for 5 seconds to help disolve benzoic acid in methanol
18:55 - Vials #1 and #3 were both placed in a hot water bath with initial temperature 50 degrees C.
19:05 - Vial #1 became a clear solution at 58 degrees C and was left in the hot water bath with vial #3.
19:10 - Vial #3 became a clear solution at 61 degrees C, indicating that the benzoic acid had dissolved completely.
19:12 - Reduced water temperature to 59 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:15 - Reduced water temperature to 58 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:20 - Reduced water temperature to 57 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:25 - Reduced water temperature to 56 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:30 - Reduced water temperature to 55 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:35 - Reduced water temperature to 54 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:40 - Reduced water temperature to 50 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
19:50 - Observed both vials after sitting in a 50 degree water bath, no precipitate.
19:51 - Reduced water temperature to 48 degrees C and placed both vials in the sonicator for 2 seconds, no precipitate. Both placed back into the water bath.
20:00 - Observed both vials at 48 degrees C, no precipitate.
20:05 - Realize that I am starving and decide to finish the experiment on wednesday, July 1st.
20:07 - Place the remaining 4 vials in a beaker labled "Anthony Shorrock, Exp118."
20:10 - Leave both vials #1 and #3 in the hot water bath overnight.

2009-07-01
16:50 - Heated water to 60 degrees C before placing vial #3 inside, which had conciderable precipitate after cooling overnight. Vial #1 remained clear at room temperature.[This is dangerous! Do not heat samples within 15C of their boiling point. Not only can they explode but you are very likely to evaporate some solvent and get false readings JCB] - stopped heating solution. Vial #3 is aborted.
17:50 - Placed 5 remaining vials into the water bath at room temperature, 25 degrees C.
17:55 - No precipitate present in the remaining vials (vials #1, #2, #4, #5, #6) at 25 degrees C.
17:57 - Reduced water temperature to 24 degrees C and placed all 5 vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
18:03 - Reduced water temperature to 23 degrees C and placed all 5 vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
18:09 - Reduced water temperature to 22 degrees C and placed all 5 vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
18:15 - Reduced water temperature to 20 degrees C, no precipitate. All vials placed back into the water bath.
18:24 - Reduced water temperature to 18 degrees C, no precipitate. All vials placed back into the water bath.
18:32 - Reduced water temperature to 16 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
18:40 - Reduced water temperature to 14 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
18:50 - Reduced water temperature to 12 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
19:00 - Reduced water temperature to 10 degrees C, no precipitate. All vials placed back into the water bath.
19:15 - Reduced water temperature to 7 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
19:20 - Reduced water temperature to 4 degrees C. Vial #1 precipitate at 5 degrees C and removed from the water bath. The remaining vials (Vial #2, #4, #5, #6) placed back into the water bath.
19:22 - Reduced water temperature to 2 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
19:28 - Reduced water temperature to 0 degrees C, no precipitate. All vials placed back into the water bath.
19:35 - Reduced water temperature to -4 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
19:45 - Reduced water temperature to -8 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
19:56 - Reduced water temperature to -12 degrees C, no precipitate. All vials placed back into the water bath.
20:08 - Reduced water temperature to -15 degrees C and placed all vials in the sonciator for 2 seconds, no precipitate. All vials placed back into the water bath.
20:20 - Reduced water temperature to -20 degrees C and placed all vials in the sonicator for 2 seconds, no precipitate. All vials placed back into the water bath.
20:35 - Vials #2, #4, #5, #6 showed no precipitation at -20 degrees C. Advised not to lower the temperature any further and to use the data obtained from the previous vials.


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