Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in benzene with the proper changes determined in (the conclusion of) EXP298

Procedure

2.0025g of benzoic acid and 2.5mL of benzene were added into a 10mL Erlenmeyer flask and set on a hot plate to boil. Once all of the solute had dissolved into the solvent, the flask was removed from the heat and set to cool down to room temperature. After it had cooled down and crystals had formed, the contents of the flask were filtered through a suction filter. The recrystallized benzoic acid was massed.

Results

Calculation Sheet
65% of the benzoic acid was recrystallized. The solubility at the boiling point was 3.93M.

Discussion

The predicted solubility at boiling temperature was approximately 3.8M with a yield of 80%.
The theoretical maximum yield was about 83% with a 4.7M solution
This experiment resulted in a solubility of approximately 3.93M at boiling point with a theoretical yield of 80.4%
The actual yield of the benzoic acid turned out to be 65% which is lower than expected.


Conclusion

The lower yield could be accounted for in this experiment due to the washing of the flask during the filtration process. This could also be accounted for due to the assumption that all of the recrystallization had occured. This can be fixed if the flask was cooled in a 25C water bath or if the flask was left overnight.


Log

2012-06-25

1:23 - Turned on hot plate to 175C
1:31 - Added 2.0025g of benzoic acid into a 10mL Erlenymeyer flask.
1:38 - Added approximately 2.5mL of benzene into same flask, put loose cap on top,and set on hot plate.
1:45 - All of the benzoic acid has dissolved into the benzene
1:46 - Removed flask from the hot plate and set to cool down;the loose cap is still on flask.
1:48 - needle-like crystals begin to appear in the flask. There is also some benzene droplets on the inside walls of the flask. There is no solvent above the crystals.
2:09 - Suction filtered the contents of the flask
2:11 - The crystals were not leaving the flask so the flask was washed twice with 3mL each time to get the crystals out.
2:23 - Mass of empty vial with cap: 13.5640g
2:28 - Mass of vial with cap and recrystallized benzoic acid: 14.8655g
2:29 - Mass of benzoic acid recrystallized: 1.3015g