Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in ethanol/water(37.5:62.5)vol due to results of EXP317 in the traditional method

Procedure

A stock solution of ethanol and water in a 12:20 volume was made. An empty 10mL erlenmeyer flask with a loose cap was weighed. About 1g of benzoic acid was placed into the flask and it was weighed again. Approximately 2mL of the stock solution was added into the flask, it was weighed, and the flask was set on the hot plate. Once all of the benzoic acid had dissolved into the ethanol/water mixture, the flask was removed from the hot plate and set to cool down. The flask was weighed again, and another time with parafilm around the cap before leaving it to cool. After crystals had fully formed, the flask was weighed again and the crystals were filtered through a suction filter and collected in a vial.

Results

Calculation Sheet
EXP319a-HNMR
The solubility at boiling point for this solution was 3.32M
With this solubility and a room temperature solubility of 0.19M, the predicted recrystallization yield was 94.28% while the actual yield was 89.6%

Discussion

According to Lab02, the solubility they created was 0.25M but we were able to reach a saturated solution with a solubility of 3.32M through the method of adding little solvent at a time until the point where the solute just completely dissolves.
According to the temperature curve, the solubility at boiling point is 2.21M and with that, a predicted recrystallization yield of 91.4%
EXP319a-HNMR shows that there is no ethanol or water left in the sample, thus the sample is dry.

Conclusion

Model003 predicted a boiling point solubility of 2.11M for benzoic acid in ethanol/water (30:70) volume however that is about 1.2M lower than what we were able to achieve in this experiment.
It is possible that the room temperature solubility of 0.19M is too high and that it could potentially be around 0.1M

Log

2012-07-16

1:34 - A stock solution of approximately 100mL was made in a 125mL erlenmeyer flask using ethanol/water in a 12:20 ratio.
1:36 - Turned hot plate on to 200C
1:56 - Mass of empty 10mL erlenmeyer flask + cap: 18.1567g
1:57 - Mass of flask, cap, and benzoic acid: 19.1976g
1:58 - Approximately 2mL of the stock solution was added into the flask and both the flask and the flask of the stock solution was put onto the hot plate with loose caps.
2:04 - All of the benzoic has dissolved into the boiling solvent without the addition of any more boiling solvent. The flask was removed from the hot plate, covered in parafilm to prevent any solvent from escapying, and set to cool down.
2:16 - Mass of flask, cap, benzoic acid, and solvent: 20.7178g
2:17 - Determined density of the ethanol/water(12:20) stock solution through a volumetric flask
2:18 - Mass of 2mL volumetric flask: 5.5404g
2:20 - Mass of volumetric flask + stock solution: 7.3304g
2:29 - Denisty of ethanol/water(12:20) stock solution: 0.895g/mL

2012-07-17

10:14 - Filtered the contents of the flask through a suction filter
10:56 - Mass of empty vial: 11.6816g
10:59 - Turned off vacuum for suction filter
11:05 - Mass of vial with exp319a crystals: 12.6138