Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in benzene

Procedure

2g of benzoic acid and 2.5mL of benzene were put into an Erlenmeyer flask and set on a hot plate to boil. All of the benzoic acid was able to be dissolved without the addition of more benzene. The flask was removed from the heat and set to cool and allow crystal formation. The crystals were filtered through a suction filter and dried.

Results

1.4124g of the initial 2.0052g were covered. This means the recrystallization yield is approximately 70%.

Discussion

Recrystallization Sheet
According to the recrystallization sheet, approximately 83% of benzoic acid dissolved in benzene should be recrystallized. This experiment only yielded about 70% which is not too far from the predicted yield. The predicted 83% yield comes from using 4.67M as the solubility at boiling point
the solubility of the benzoic acid in benzene at its boiling point was approximately 3.6M. The predicted solubility for this was 3.8M


Conclusion

Probably used inappropriately sized Erlenmeyer flask because surface area affects recrystallization. The recrystallization yield also could have been affected due to the removal of the cap off the Erlenmeyer flask when it was set down to cool; solvent would have evaporated while cooling down to room temperature. This experiment is going to be repeated with an appropriate sized Erlenmeyer flask along with sufficient cooling time.


Log

2012-06-20

12:43 – turned on hot plate to 175C
12:46 – added 2.0052g of benzoic acid into a 50mL Erlenmeyer flask
12:50 – added 2.5 mL of benzene into the same Erlenmeyer flask and set on hot plate
12:53 – added about 20mL of benzene into another Erlenmeyer flask and set on hot plate to boil
12:57 – Removed the flask from the hot plate because all of the benzoic acid dissolved. No additional benzene had to be added into the flask. [Was the solution boiling? JCB]
12:58 – crystals have formed
1:03 – Filtered the contents of the flask through a suction filter
1:19 – mass of empty vial with cap: 13.6655g
1:26 – mass of vial with recrystallized benzoic acid and cap: 15.0779g
1:26 – mass of benzoic acid recovered: 1.4124g