Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in hexane, because it was predicted to be a good solvent.

Procedure

1.0359g of benzoic acid and 14.4164mL of hexane were added into a 25mL Erlenmeyer flask and set on a hot plate to boil. Once all of the benzoic acid had dissolved into the hexane, the flask was removed from the hot plate and set to cool down over night. The crystals that formed inside the flask were filtered through a suction filter and massed.

Results

Calculation Sheet
EXP306-HNMR
The solubility of benzoic acid in hexane at its boiling point was 0.5555M.
The predicted recrystallization yield based off a solubility of 0.5555M was 86.5% while the actual yield in this experiment was 85.6%

Discussion

According to ksiazczak86 the solubility of benzoic acid in hexane at boiling point should be around 0.61M which means about 88% of the crystals would be yielded back since the room temperature solubility is 0.075M.
According to the solubility curve, the solubility at boiling point is 0.95M which means that there would be a recrystallization yield of about 92%.
When hexane was used to recrystallize cinnamic acid in EXP281 and EXP292 they had very low recrystallization yields (64% and 54% respectively), but when it was used to recrystallize benzoic acid, it yielded back as much as it predicted.
The NMR spectra shows that the there is no hexane left in the sample, so the sample is completely dry.

Conclusion

The solvent selector predicted the solubility of benzoic acid in hexane very well.
Hexane is a good solvent to use to recrystallize benzoic acid.
From the results of previous experiments with cinnamic acid, there could be a problem with the cinnamic acid that is giving us very off results because hexane did not give unusual results for benzoic acid.

Log

2012-07-02

11:54 - Turned on hot plate to 170C
12:39 - 1.0359g of pebble-like benzoic acid was added into 25mL Erlenmeyer flask.
- Mass of 25mL Erlenmeyer flask with cap: 41.1346g
- Mass of flask with cap and benzoic acid: 42.1705g
12:41 - Approximately 10mL of hexane was added into the flask and set on hot plate to boil
12:43 - A small flask with just hexane was set on hot plate to boil.
12:54 - Added approximately 2mL of boiling hexane into flask
1;00 - Added approximately 0.5mL of boiling hexane into flask
1:02 - Added approximately 0.5mL of boiling hexane into flask.
1:04 - Added approximately 0.25mL of boiling hexane into flask.
1:12 - All of the benzoic acid has dissolved into the hexane and the flask was removed from the hot plate
1:12 - The flask was set to cool down over night.
1:13 - Needle-like crystals begin to form on the bottom of the flask
1:18 - Mass of flask with cap, benzoic acid, and approximately 14mL hexane: 51.9160
- Mass of hexane in flask: 9.7455g (equivalent to 14.4164mL)

2012-07-03

9:40 - Filtered the needle-like crystals through a suction filter
9:44 - The crystals look fluffy when clumped together
9:55 - Stopped the vacuum for the filter and collected crystals in a vial
9:57 - Mass of empty vial with cap: 13.6059g
10:01 - Mass of vial, cap, and crystals: 14.4930g