Researcher

Rida Atif

Objective

To measure the recovery of trans-cinnamic acid through re-crystallization using n-hexane.

Procedure

Dissolve about 250mg trans-cinnamic acid in about 10mL of boiling n-hexane in an Erlenmeyer flask, adding about 1mL of n-hexane to the flask at a time until all of the cinnamic acid dissolves. Remove the flask from the hotplate and allow it to cool until crystals appear. Filter the contents of the flask and take the mass of the crystals left behind from the filtration.

Results

The weight of the recovered cinnamic acid was 0.1161g. This is only 64.44% of the original mass of trans-cinnamic acid.

Discussion

The yield of the cinnamic acid was 64.44% while the theoretical yield is approximately 99.6%. The solubility of cinnamic acid in n-hexane at room temperature is 0.04M, but when the solubility was calculated using the data from this experiment it was 0.06M (this is significantly smaller). The yield is low partly due to some of the contents of the flask spilling onto the counter while transferring from the flask to the filter. Other possible reasons for the low yield are that the cinnamic acid could have had impurities or that the solubility of cinnamic acid in n-hexane at room temperature is off by an order of magnitude.

Conclusion

The yield of the recrystallized cinnamic acid in n-hexane in this experiment is 64.44%, but other experiments have had higher yields, so something happened during this experiment that is yet to be determined.

Log

2012-16-04

12:16 - 255.3mg of trans-cinnamic acid was put into an Erlenmeyer flask.
12:18 - 10mL of n-hexane was poured into the same Erlenmeyer flask.
12:19 - Turned on hot plate to 190C.
12:27 - Placed Erlenmeyer flask onto hotplate.
12:30 - Turned down the hot plate to 115C and added approx. 1mL n-hexane to flask since not all of the acid was dissolving.
12:32 - Turned hot plate up to 130C and added another approx. 1mL n-hexane to flask.
12:35 - added approx 1mL n-hexane to flask.
12:36 - turned hot plate up to 160C.
12:37 - added approx 1mL n-hexane to flask.
12:38 - added approx 1mL n-hexane to flask.
12:40 - added approx 1mL n-hexane to flask. (by this time a total of 20mL of n-hexane is in flask; a total of 10 additional milliliters of n-hexane has been added to the flask).
12:44 - added approx 1mL n-hexane to flask.
12:47 - added approx 1mL n-hexane to flask.
12:49 - added approx 1mL n-hexane to flask.
12:51 - added approx 1mL n-hexane to flask.
12:54 - added approx 1mL n-hexane to flask.
12:58 - added approx 1mL n-hexane to flask. (by this time a total of 26mL of n-hexane is in the flask; a total of 16 additional milliliters of n-hexane has been added to the flask).
13:02 - Used a metal spatula to crush chunk of cinnamic acid and also scraped some acid off inside wall of the flask.
13:07 - All of the cinnamic acid has dissolved into the n-hexane.
13:08 - Removed flask from hot plate and set down to cool.
13:10 - Small amounts of crystals start to appear on inside walls of flask.
13:19 - Scratched off some crystals off inside walls of flask with metal spatula to increase crystal formation.
13:37 - Filtered contents of flask through suction filtration.
13:48 - Took mass of empty vial with cap (5.2397g)
13:50 - Took mass of vial with crystals and cap (5.4008g)