[remove all span tags JCB]

Researchers

Lacey Condron and Andrew Lang

Objective

To recrystallize cinnamic acid using hexane.

Procedure

Hexane was obtained, volumetric flask was weighed (20.344 g) and the weight of 25 ml of hexane (16.538 g) was obtained from the electronic balance. Contents of the flask were transferred to a 125 mL Erlenmeyer flask. The amount of cinnamic acid was previously calculated to make a 1.00 M using the Planning Sheet. Cinnamic acid (0.954 g) was weighed and added to the beaker; this procedure was done in a room with a measured temperature at 22.0 degrees C. After the cinnamic acid was added, a stopper was used instead of parafilm because of hexane's high volatility resulted in the parafilm dissolving quickly after application and to ensure that spilling, contamination and vaporization of the liquid did not occur.The beaker was placed in a hot water bath (tap water) at 60 degrees C to allow the solute to fully dissolve.The beaker was swirled periodically to assist in dissolving the solute. The hot water bath was heated to approximately 68 degrees C and the solute was still not fully dissolved. After about 10 minutes, the experiment was abandoned because it would not dissolve. The volumetric flask was weighed (20.365 g) and the weight of 25 mL of hexane (16.457 g) was obtained from the electronic balance. Contents of the flask were placed in an Erlenmeyer flask with a stopper because the hexane's high volatility caused the parafilm to be disintegrated and result in vaporization of hexane. The amount of cinnamic acid was cut in half, to attempt to get a 0.05 M solution. The cinnamic acid (0.478 g) was weighed and added to the Erlenmeyer flask. The Erlenmeyer flask was placed in a 65 degree water bath and was swirled periodically to assist in dissolving the solute. After sitting in the water bath for 10 minutes the solute was still not dissolved. Because hexane has a boiling point of 68 degrees C, the solvent should have dissolved already. These two experiments were abandoned because they would not dissolve.
Two more solutions were made with smaller amounts of cinnamic acid. A 25 ml flask was weighed and the weight was recorded. 25 ml of hexane was measured out and put into the flask. The hexane was weighed (16.682 g) then it was transferred to a 125 ml Erlenmeyer flask. The amount of cinnamic acid was cut in half from the previous experiment, therefore 0.236 g of cinnamic acid was weighed and added to the Erlenmeyer flask. The flask was labeled and placed in a 65 degree C water bath. The flask was swirled periodically to assist in dissolving. The same procedure was used for another solution but this time, only 0.118 g of cinnamic acid was used. Both flasks were placed in the water bath and after about 2 minutes, the flask with 0.118 g fully dissolved, and after 7 minutes, the flask with 0.236 g fully dissolved. Both flasks were removed from the hot water bath and were placed in the fume hood to cool to room temperature.
The 3rd solution that was made which used 0.236 g of cinnamic acid was left to cool to room temperature. Once the solution was fully cooled, the recrystallization process began. The filtering apparatus was assembled using thick rubber tubing, connected to the vacuum. The other end of the rubber tubing was connected to the filtering flask, then the Buchner funnel was placed inside the flask with a piece of filter paper. Hexane was used to moisten the filter paper then the contents of the flask was carefully transferred from the flask onto the filter paper. To help get all of the crystals outs of the flask, hexane was used to rinse the flask to catch any remaining crystals. Once all the crystals were removed from the flask the product was vacuumed for 15 minutes. This procedure was performed in a room with a temperature of 20.5 degrees C. The vacuum was turned to the off position, then the funnel with the filter paper was removed from the flask so that all the crystals could be obtained. A piece of weigh paper was prewieghed and the scale was zeroed. Then all the crystals on the filter paper and the funnel were put onto the weigh paper. The first weight of the crystals was 0.182. The crystals were put back onto the filter paper and the vacuum apparatus was put back into place so that the product could be dried for a few more minutes, ensuring that all of the hexane was dried out and that the weight was purely cinnamic acid. After about 5 minutes of drying once more, the vacuum was turned off and the crystals were reweighed. The second weight of the crystals was 0.186 g. The differences in these values are likely due to the crystals absorbing the air causing them to weight slightly more. The initial weight of the crystals, 0.182 g will be used in the calculations.

Results

Weight of the dried recrystallized from hexane, trans-cinnamic acid was measured to be 0.182 g. [Assuming this is from solution #3, this would correspond to a 79% apparent yield. JCB]

Conclusion

[This yield is much higher that would be expected from the corresponding experiment EXP281 , where 94 mg should be left in the 25 ml of filtrate instead of the apparent 50 mg here. One explanation for this higher apparent yield would be evaporation of the solvent. JCB]


Log

Solution #1
9:12 Weighed 25mL volumetric flask- (20.344 g)
9:13 Pipetted 25mL of hexane into the previously weighed volumetric flask. Weighed 25mL of hexane- (16.538 g)
9:14 Poured the previously weighed 25mL of hexane into 125mL beaker and used a stopper to prevent evaporation.
9:20 Weighed/ added cinnamic acid (0.954 g) at 22.0 degrees C.
9:21 Placed beaker in 60 degree C water bath using tap water.
9:22 Beakers were continuously swirled to assist in the dissolving process while the temperature of the water bath was maintained to stay within 68 degrees C.
9:35 Solute was not dissolved, experiment abandoned.
Solution #2
9:16 Weighed 25mL volumetric flask- (20.365 g)
9:18 Pipetted 25mL of hexane into the previously weighed volumetric flask. Weighed 25mL of hexane- (16.457 g)
9:19 Poured the previously weighed 25mL of hexane into 125ml Erlenmeyer flask with stopper.
9:23 Weighed/ added cinnamic acid (0.478 g) at 22.0 degrees C.
9:25 Placed beaker in 60 degree C water bath using tap water.9:26 Beakers were continuously swirled to assist in the dissolving process while the temperature of the water bath was maintained to stay within 68 degrees C.
9:35 Solute was still not dissolved, experiment abandoned.
Solution #3
9:36 Weighed 25 mL volumetric flask- (20.043 g)
9:39 Pipetted 25 mL of hexane into the previously weighed volumetric flask. Weighed 25 mL of hexane- (16.682 g)
9:40 Poured the previously weighed 25 mL of hexane into 125 mL Erlenmeyer flask. Placed stopper on flask.
9:41 Weighed/ added cinnamic acid (0.236 g) at 22.0 degrees C.
9:43 Placed beaker in 60 degree C water bath using tap water.
9:44 Beaker was continually swirled to assist in the dissolving process while the temperature of the water bath was rising steadily to reach the boiling point of hexane, 68 degrees C.
9:50 The temperature reached 68 degrees C and the solute was fully dissolved. The beaker was removed from the hot water bath and placed in the fume hood at room temperature to cool.
Solution #4
9:43 Weighed 25 mL volumetric flask- (20.149 g)
9:44 Pipetted 25 mL of hexane into the previously weighed volumetric flask. Weighed 25 mL of hexane- (16.560 g)
9:45 Poured the previously weighed 25 mL of hexane into 125 mL Erlenmeyer flask. Placed stopper on flask.
9:47 Weighed/ added cinnamic acid (0.118 g) at 22.0 degrees C.
9:48 Placed beaker in 60 degree C water bath using tap water.
9:49 Beaker was continually swirled to assist in the dissolving process while the temperature of the water bath was rising steadily to reach the boiling point of hexane, 68 degrees C.
9:52 The temperature reached 68 degrees C and the solute was fully dissolved. The beaker was removed from the hot water bath and placed in the fume hood at room temperature to cool.
**The recrystallization was performed on a different day.
9:30 Assembled the vacuuming apparatus.
9:32 Began transferring the crystals onto the filter paper.
9:34 Washed the flask with hexane to ensure the full removal of the crystals.
9:37 All of the crystals had been removed from the flask and onto the filter paper.
9:40 The product was left to vacuum for approximately 15 minutes.
9:55 The product was taken off the vacuum and the crystals were weighed.
10:00 The crystals were put back into the vacuum and set to dry for a few more minutes
10:05 The crystals were removed from the vacuum and weighed for the final value which was 0.186 g.