Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in carbon tetrachloride

Procedure

An empty erlenmeyer flask and cap were massed empty. About 1g of benzoic acid was added into the flask and massed again. Approximately 1.5mL of carbon tetrachloride was added to the same flask and set on hot plate. CCl4 was added into the flask until all of the benzoic acid dissolved; after all of the benzoic acid dissolved into the solvent, the flask was removed from the hot plate, massed, then set to cool down. The mass of the flask was taken again before filtering, and the contents of the flask were filtered through a suction filter. The crystals were massed.

Results

Calculation Sheet
The melting point of the exp315a was between 121C and 122C.
The solubility of the solution at boiling point was 3.5M
The predicted recrystallization yield at that solubility is approximately 84% (with a room temperature solubility of 0.57M), whereas the actual yield in this experiment was 94%

Discussion

Model003 predicted carbon tetrachloride would be an excellent solvent to use to recrystallize benzoic acid, given that the solubility at boiling point was 1.55M and room temperature was 0.105M. With these solubilities, the predicted recrystallization yield would have been 93%
According to the temperature curve, the solubility at boiling point should have been 3.06M with a recrystallization yield of about 82%
The actual solubility at boiling point was 3.5M, and the actual yield was higher than the predicted yield for this particular solubility. The actual yield is higher than the predicted because about 40% of the CCl4 evaporated overnight (this can be seen in the difference between the mass of the flask after it was left overnight).
The melting point of benzoic acid is 122C, so the melting point of exp315a is right on point meaning that the crystals are completely dry.

Conclusion

In this case, the solvent selector did not predict extremely accurately for the solubility of benzoic acid in CCl4 as it was able to do for the solubility of the same solvent with cinnamic acid in EXP316.
Even though solvent selector did not predict exactly, Model003 was accurate in predicting that CCl4 is a good solvent to recrystallize benzoic acid from.
The issue of the artificially high yield due to the solvent evaporating overnight will be addressed by covering the top of the flask with parafilm to completely seal the opening from now on.

Log

2012-07-11

11:11 - Turned on hot plate to 170C
11:44 - Used 0.8592g of the benzoic acid recrystallized in EXP303 and added that into a 10mL erlenmeyer flask
11:48 - Added about 1.5mL of carbon tetrachloride into the same flask and set on hot plate
11:54 - All of the benzoic acid dissolved into the CCl4 without additional solvent. The flask was removed from the hot plate and set to cool down.

2012-07-12

10:59 - Filtered contents of flask through a suction filter
11:05 - The crystals (exp315a) are needle-like
11:24 - Mass of empty vial and cap: 13.6299g
11:26 - Stopped the vacuum for the filter
11:30 - Mass of vial, cap, and crystals: 14.4403g