Researcher

Rida Atif

Objective

To determine the recrystallization yield of cinnamic acid in n-hexane

Procedure

0.4932g of cinnamic acid and 5mL of hexane were added into a 25mL Erlenmeyer flask and set on a hot plate. More hexane was added into the flask until all of the cinnamic acid had dissolved into the hexane. The flask was then removed from the hot plate then set to cool down over night. The crystals that formed in the flask were filtered through a suction filter and massed.

Results

Calculation Sheet
EXP310-HNMR
The solubility of the solution at boiling point was 0.1545M
The predicted recrystallization yield for this solubility was about 75% while the actual yield ended up being 86.94%

Discussion

The NMR spectrum shows that there is an extremely small amount of hexane left in the sample due to the peak at 0.9. This trace amount of solvent does not affect the yield of crystals.
According to the solubility curve, the solubility of this particular solution should have been 0.51M at boiling point.
Previous experiments that dealt with determining the solubility of cinnamic acid in hexane at boiling point resulted in numbers more similar to the result of this experiment rather than the predicted solubility.
For example, in EXP281, the solubility was determined to be 0.06M
in EXP285, the solubility was 0.164M
in EXP291, the solubility was 0.13M
in EXP292, the solubility was 0.057M
The yield could be artificially high because hexane could have evaporated from the flask while it was left over the weekend.

Conclusion

There could be a problem with the solvent selector for this particular combination, or the temperature curves could be overpredicting solubilities for cinnamic acid in general.
To test this theory, EXP312 will use benzene to recrystallize cinnamic acid. Benzene turned to be a good solvent for benzoic acid and the temperature curve predicted very accurately for the solubility at boiling point.
This experiment will be repeated with a tighter seal on the flask so that hexane does not evaporate at all while the solution cools down


Log

2012-07-03

10:32 - Turned on hot plate to 170C.
12:13 - Turned heat up to 210C
12:55 - Turned down heat to 130C
1:04 - Added 0.4932g of cinnamic acid into a 25mL erlenmeyer flask
1:06 - Added 5mL of hexane into flask and set on hot plate.
1:07 - Added hexane into another small flask and set that on hot plate too.
1:11 - Added approximately 1mL of boiling hexane into flask
1:18 - Added approximately 1mL of boiling hexane into flask.
1:37 - Added approximately 1mL of boiling hexane into flask.
1:44 - Added approximately 1mL of boiling hexane into flask
1:45 - Turned up hot plate to 175C
1:50 - Added approximately 1mL of boiling hexane into flask.
2:10 - Added approximately 1mL of boiling hexane into flask.
2:16 - Added approximately 1mL of boiling hexane into flask.
2:30 - For some reason the hexane was evaporating quickly even with the loose cap on, so approximately 5mL hexane was added into flask
3:04 - all of the cinnamic acid has dissolved into the hexane, the flask was removed from the heat and set to cool down

2012-07-05

11:50 - Filtered contents of the flask through a suction filter.
11:54 - The crystals look like specks of glitter
12:16 - Mass of empty vial and cap: 13.5693g
12:17 - Stopped the vacuum of the filter
12:23 - Mass of vial, cap, and cinnamic acid (EXP310a): 13.9981g