Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in benzene with the appropriate changes determined in (the conclusion of) EXP299

Procedure

2.007g of benzoic acid and 2mL of benzene were added into a 10mL Erlenmeyer flask and set to boil. Once all of the benzoic acid had dissolved into the benzene, the flask was removed from the heat and set to cool down overnight in order to encourage the formation of crystals. The crystals were filtered through a suction filter and taken the mass of.

Results

Calculation Sheet
The solubility of the solution at the boiling point was 4.475M.
The recrystallization yield in this experiment was 93.94%

Discussion

Since the solubility of the solution at the boiling point was approximately 4.5M, it was expected that about 83% of the benzoic acid would be recrystallized.
This correlates very well with the solubility of benzoic acid in benzene at 80C determined in Chipman's experiment which was about 4.7M.
The predicted solubility at the boiling point was approximately 3.8M, which would yield about 80% of the benzoic acid.
The actual yield in this experiment turned out to be about 94%. This is an excellent yield because it is near impossible to have a yield of 100%.
This experimental yield also hints that the concentration of the solution was very close to what it should be for the highest recrystallization yield.

Conclusion

The higher recrystallization yield in this experiment as compared to the yields in EXP298 and EXP299 shows that there definitely was an error when it came to the handling of the equipment and the recrystallization method in the previous experiments. In the other experiments, the cap was not on the flask, the crystals were washed while being filtered, and sufficient cooling time was not provided. This experiment did not have any of these mistakes, and resulted in a near perfect recrystallization yield.

Log

2012-06-27

11:04 - Turned on hot plate to 170C
11:13 - 2.0070g of benzoic acid were added into a 10mL Erlenmeyer flask.
11:18 - Added 2mL of benzene into same flask, put a loose cap on, and set on hot plate.
11:28 - Set another flask on hot plate with benzene to boil.
11:30 - All of the benzoic acid has dissolved in the benzene without the addition of any more bezene.
11:32 - The flask was removed from the flask and set to cool down to room temperature.
11:32 - needle-like crystals started to create as soon as the flask was lifted from the hot plate

2012-06-28

12:02 - Filtered the contents of the flask through a suction filter. No benzene was used to wash out crystals in the flask.
12:13 - Mass of empty vial with cap: 13.5427g
12:16 - Stopped filtering the benzene from the benzoic acid
12:17 - Mass of vial and cap with recrystallized benzoic acid: 15.4281g
12:18 - Mass of benzoic acid recrystallized: 1.8854g (94% recovered). [make sure to also get an NMR to [[#|confirm]] that solvent is not contaminating JCB]