Researcher

Matthew McBride

Objective

To recrystallize benzoic acid from n-hexane using the sintered glass funnel method

Procedure

A 0.25M solution of benzoic acid in n-hexane was created in a 10 mL test tube and dissolved at the boiling point of n-hexane using a water bath. The crystals were cooled to room temperature, vacuum filtered using a sintered glass funnel and dried over air.

Results

Recrystallization Sheet
Concentration: 0.25 M
Amount of Product Recovered: 0.1313 g
Yield: 59%

Discussion

The predicted solubility of benzoic acid in n-hexane at the boiling point is 0.9 M, but this experiment found that at the boiling point the solubility was 0.25 M. However, this measured solubility of 0.25 M may be inaccurate as it is based on the amount of n-hexane known to have been added to the solution. Some of the n-hexane may have evaporated off as the solution reached the boiling point and this loss of n-hexane is unaccounted for and would have caused the solubility at the boiling point to be greater than 0.25 M. The way to accurately determine the amount of n-hexane in the solution is to weigh the vial after the crystals have all dissolved in to determine the final weight of solvent added.

The predicted recrystallization yield with the boiling point solubility of 0.9 M is 92%. With a boiling point solubility of 0.25 M, the predicted recrystallization yield is 70%. The experimentally measured recrystallization yield was determined to be slightly less than this at 59%.

Conclusion

The solubility of benzoic acid in n-hexane was measured to be 0.25 M at the boiling point and the recrystallization yield was measured to be 59%.

Log

2013-04-12

10:33 A beaker filled with water was placed on the hot plate and the heat was turned on.
11:16 0.2229 g of benzoic acid was added to a 10 mL screw cap test tube (Tube #1).
11:30 1.7527 g of n-hexane was added to the test tube and the test tube with the cap loosely on top was placed in the hot water bath.
11:38 The solution reached a boil and all of the crystals had not entered the solution. An additional 0.5515 g of hexane was added and tube #1 was placed back in the hot water bath.
11:40 The solution reached a boil and all of the crystals had not entered the solution. An additional 0.4881 g of hexane was added and the tube #1 was placed back in the hot water bath.
11:42 The solution reached a boil and all of the crystals had not entered the solution. An additional 0.7281 g of hexane was added and the tube #1 was placed back in the hot water bath.
11:45 The solution reached a boil and all of the crystals had not entered the solution. An additional 0.7223 g of hexane was added and the tube #1 was placed back in the hot water bath.
11:50 The solution reached a boil and all of the crystals had not entered the solution. An additional 0.5723 g of hexane was added and the tube #1 was placed back in the hot water bath.
11:52 All of the crystals entered the boiling solution. Tube #1 was removed from the hot water bath and allowed to cool at room temperature.
11:55 Crystals were visible in the tube #1.
13:14 The content of tube #1 had formed a liquid gel and was placed on the 15 mL sintered glass funnel using the spatula.
13:19 1 mL of hexane was used to complete the transfer of the crystals from tube #1 to the funnel. The vacuum was applied and the crystals were filtered. Some crystals were visible in the filtration flask. The crystals were spread across the surface of the funnel to dry.
13:43 The filtration flask was removed from the suction. The weight of the funnel with the crystals was 16.6441 g.
13:55 The weight of the 5-dram vial (no cap) was 11.7943 g.
13:58 The crystals were removed from the funnel and placed in the 5-dram vial. The total weight of the vial with the crystals (Product A) was 11.9256 g.
14:15 The sintered glass funnel was cleaned and weighed empty to be 16.5404 g.