Researcher

Rida Atif

Objective

To determine the recrystallization yield of benzoic acid in cyclohexane

Procedure

1.0246g of benzoic acid and approximately 2.85mL of cyclohexane were added into a 10mL Erlenmeyer flask and set on hot plate to boil and dissolve the acid. Once all of the benzoic acid had gone into the solvent, the flask was removed from the hot plate and set to cool down over night. The crystals that formed in the flask were filtered through a suction filter and massed.

Results

Calculation Sheet
EXP305-HNMR
The solubility at the boiling point was 2.2654M.
The predicted recrystallization yield from that solubility was approximately 95.5% while the actual yield was 94.1%

Discussion

According to Ksia̧żczak86 the solubility of benzoic acid in cyclohexane at its boiling point should be 2.0311M which means that there should be almost a 95% recrystallization yield since the solubility at room temperature is 0.103M.
According to the solubility curve, the solubility at boiling point should be approximately 2.000M, so the yield should also be about 95%
The predicted experimental yield was about 95.5% and the actual yield was 94.1% which is very close to the ones predicted by the temperature curve as well as literature.
The NMR spectra displays that there is a peak at 1.5 that could be cyclohexane or water, but it is not enough to significantly affect the yield.

Conclusion

The solvent selector predicted very well for the solubility of benzoic acid in cyclohexane
Cyclohexane is a good solvent to use to recrystallize benzoic acid.

Log

2012-07-02

11:54 - Turned on hot plate to 170C
12:08 - Mass of empty 10mL erlenmeyer flask with loose cap: 18.1558g
- Mass with benzoic acid: 19.1804g
- Mass of powder-like benzoic acid in flask: 1.0246g
12:14 - Approximately 3mL of cyclohexane was added into the flask and set on hot plate
- Mass of flask with cap, benzoic acid, and 3mL cyclohexane: 21.4354g
12:17 - Another small flask with just cyclohexane was also set on hot plate to boil
12:27 - All of the benzoic acid dissolved into the cyclohexane without the addition of any more solvent
- Crystals started to form as soon as the flask was removed from the heat
12:27 - The flask was removed from the hot plate and set to cool down over night.

2012-07-03

9:11 - Filtered the needle-like crystals through a suction filter.
9:28 - Stopped the vacuum for the suction filtered and collected dry crystals (EXP305a) in a vial
9:30 - Mass of empty vial with cap: 13.5929g
9:34 - Mass of vial, cap, and crystals: 14.5572g