Researchers

Lacey Condron with Lizzie Clark and Samantha Gaines

Objective

To calculate the solubility of trans-cinnamic acid in ethanol by density method. The additivity of volumes is an assumption and the density of the solute is obtained from ChemSpider.

Procedure

Ethanol solution was obtained, volumetric flask was weighed and the weight of 25 ml of ethanol solution was obtained from electronic balance. Contents of flask was transferred to 100 ml beaker. Cinnamic acid was added using a microspatula. After each addition, the beaker was swirled to allow contents to dissolve. After multiple additions of cinnamic acid, the beaker was placed in a hot water bath at 36 degrees C to allow more solute to dissolve. After the contents dissolved, more solute was added. This procedure was followed until the amount of cinnamic acid added was all dissolved, but was achieved only by a long period of heating and swirling. The beaker was covered with parafilm and was left to cool to room temperature. After sitting for approximately 1 hour, crystals formed.

Results

https://docs.google.com/spreadsheet/ccc?key=0Au_5J1f583GgdGNGcTdxZVlUYy1jWU1ISlhEdTJ1Q1E&hl=en_US
[If you can get a pic of the volumetric with the meniscus line showing that would be helpful. JCB]
[I didn't get a picture of that, but I will next time. LNC]

Discussion

The solution used was ethanol, which only has a two-carbon chain. Because of this, the solute was very soluble in this solvent. This resulted in a large amount of cinnamic acid being added before the solution reached the saturation point. The following is an image of ethanol.
ethanol.htm
The image below is during the addition of cinnamic acid, this solution is almost to the saturation point.
2011-10-03_10.58.02.jpg
The solution began to turn a yellow color as it neared the saturation point. In this experiment, a beaker was used to hold the ethanol solution (30 mL) and the cinnamic acid was added using a microspatula. This method was the most effective because the cinnamic acid wasn't getting stuck onto the sides of the volumetric flask during the additions to the solution. By using 30 mL of ethanol instead of 25 mL of ethanol, once the saturated solution had been formed, crystals developed on the bottom of the beaker and there were still some crystals floating in the solution. This made it difficult to decant the solution, by having a little more solution than necessary it was easier to obtain 25 mL of saturated solution from the beaker. This method was more sanitary, and it didn't create a mess on the lab bench, as did the method of using only the volumetric flask.

Conclusion

The shorter the carbon chain on an acid, I conjecture that the more soluble it will be, therefore the longer the carbon chain of the solvent, the less soluble it will be. [Back this up with predicted values - maybe do a graph. AL] The molar concentration of trans-cinnamic acid is 1.1040 M. [Compare with other measured ethanol values AL]

Log

2011-10-03

09:37 - Used electronic balance to weigh ethanol solution in 25 ml volumetric flask at room temperature, or 20.4 degrees C. 10 mL of ethanol weighed 19.7781 g.
10:02 - Contents of volumetric flask were transferred to beaker to allow for easier addition of acid. 5 ml of excess ethanol was added to 100 ml beaker to ensure that after experiment, exactly 25 ml of solution could be obtained.
10:04 - Began adding cinnamic acid, swirling beaker between each addition. Cinnamic acid readily dissolved with each addition after simple swirling.
10:29 - Cinnamic acid began to delay to dissolve, beaker was placed on stand in 36 degree C water bath for 6 minutes to help dissolve, swirling periodically.
10:35 - Took beaker out, swirled, and added additional cinnamic acid.
10:37 - Beaker was placed back in 36 degree C water bath for 4 minutes. At this point, the cinnamic acid was having trouble dissolving.
10:40 - Removed beaker from water bath and added additional cinnamic acid.
10:44 - Put beaker back in 38 degree C water bath for 3 minutes.
10:47 - Added additional cinnamic acid and placed beaker in water bath at 38 degrees C for 2 minutes.
10:54 - Added additional cinnamic acid and placed beaker in water bath at 39 degrees C for 3 minutes.
11:00 - Additional cinnamic acid was added, beaker was placed back into water bath at 39 degrees C for 2 minutes. At this point, each addition add difficulty dissolving, which resulted in the beaker needing to be heated after each addition.
11:05 - The last addition of cinnamic acid eventually dissolved after swirling and heating. The beaker was covered with parafilm and left to cool to room temperature to see if the solution was saturated.

2011-10-05

12:00 - Solution was checked and crystals formed in beaker, indicating a saturated solution.
The experiment was continued on 10-5-11 to determine the density of the solution through the determination of the weight of 25 mL of saturated solution.
12:16 - The balance was zeroed and the weight of the 25 mL volumetric flask was obtained to be 20.0407 g.
12:17 - 25 mL of saturated solution from the beaker was pipetted into the previously weighed 25 mL volumetric flask.
12:20 - The weight of 25 mL of saturated solution was obtained to be 21.1862 g
12:22 - The glassware was washed and put away. This concluded this experiment.