CHEM 221 Lab Report #5 PDF

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Experiment 5: Liquid-Liquid Extraction Purification of Benzoic Acid

Name: Anonymous ID: [00000000] Partner: Anonymous

Lab Section: 08L Date Performed: March 5th, 2020 Date Submitted: March 12th, 2020

Introduction: The objective of Experiment #5 was to purify a sample of benzoic acid contaminated with salt (NaCl) through liquid-liquid extraction techniques. The method of liquid-liquid extraction works to purify organic substances by using two immiscible liquids, meaning the liquids do not mix with one another due to their different polarities, to separate our solid (benzoic acid) The layers in which the liquids assemble into in the separatory funnel depends on the densities of the solvents. The organic being either denser, will separate below the water level, or less dense than water, will separate as the top layer. The principle of the method is that if a substance is soluble to some extent in both immiscible liquids, most of it can be transferred from one liquid to the other by a process that involves thorough mixing of the liquids. It also involves hydrophobicity, in that “like dissolves like '', so polar molecules will readily dissolve in polar solvents, whereas non-polar substances will dissolve in nonpolar solvents. In our particular experiment, we used benzoic acid (a carboxylic acid), which is a weak organic acid that is deprotonated using a base (NaOH) would be more water-soluble because the resulting solvent would carry a charge and allow the polar molecules to mix.

Results: Data Table for Benzoic Acid Obtainment

vial #1

vial weight (g)

vial weight with acid (g)

calculation

Benzoic acid weight (g)

13.002 g

15.506 g

15.506 g - 13.002 g = 2.504 g

2.504 g

Observations:

Extraction process did not have any noticeable color changes to the solvent in the separatory funnel, however there is a noticeable separation between the different liquid densities Calculation of Yield equation

calculation

percent yield = (actual yield) / (theoretical yield) x 100%

1.138 g / 1.752 g = 0.6495 x 100%

percent yield 64.95%

Densities of Solvents Solvent

Density (g/ml)

diethyl ether

0.713 g/ml

ethyl acetate

0.902 g/ml

water

1.00 g/ml

Distribution Coefficient equation

calculation

theoretical yield

K = [solute] organic [solute] aqueous or

K = [2.5 g/30 ml] [2.5 g/21 ml]

K * sample (2.504 g) =

K = 0.6998

1.752 g

K = [concentration of A in S2] [concentration of A in S1]

Discussion: Liquid-liquid extraction involves the process of transferring a substance from a liquid or solid mixture to a solvent is called extraction, and the solvent is called the extraction solvent. The extraction solvent we used (ethyl acetate) is usually a low-boiling organic solvent that can be evaporated after extraction to isolate the wanted substance.

The extraction method was carried out by shaking the liquids in a separatory funnel. This allows us to open the funnel’s stopcock to drain the denser layer into a beaker and the liquid layers to separate sharply. We repeated the process several times to transfer most of the desired substance to the extraction solvent. We started the procedure by transferring the benzoic acid contaminated with table salt and adding the solutions of hydrochloric acid and ethyl acetate. After adding the solutions to the separatory funnel, we noticed the partition in the different densities of the liquids, and carefully drained the lower aqueous phase into a beaker. We then added water and repeated the wash. From what we know about densities, the layer with ethyl acetate is less dense than water, and will form the top layer. This means that our product (benzoic acid) is miscible with hydrochloric acid and is deprotonated. The NaCl had mixed with the water, as both are highly polar, and was extracted and poured out into the beaker.

We then add more NaOH into the separatory funnel and repeat the extraction. We know that both benzoic acid and ethyl acetate are insoluble in water because they are both almost nonpolar, therefore in order to separate the benzoic acid from ethyl acetate, NaOH is used to ionize the carboxylic acid to sodium benzoate. Then the HCl is added in order to protonate the sodium benzoate back to benzoic acid. Then, the benzoic acid will be ready to precipitate in water.

Complications during the experiment might have arisen out of an emulsion forming at the interface between the two liquids (an emulsion usually contains microscopic droplets of one liquid suspended in another). This can be solved by using a wooden application to stir the liquids gently at the interface. Another cause of error is noticing bubbling or foaming in the separatory funnel, which is a sign of a chemical reaction from the solvent and the extractive solvent reacting with each other that yield a gas, usually carbon dioxide. In this case, don’t shake the mixture, but stir it until the reaction has subsided and start shaking gently with frequent ventilation. An alternative method of separation is liquid-solid extraction. This method works by removing one or more components of a solid by mixing the solid with an extraction solvent and separating the resulting solution from the solid residue. It is often used to separate substances from natural products and other solid products. Some improvements that could’ve been done to better the separation during an extraction is to add enough of the salt (NaCl) to the separatory funnel to saturate the aqueous layer, and shake to dissolve the salt. The adding of the salt reduces the solubility of the organic compound in the water and thus promotes the quality of separation. This method can also be used to increase the amount of organic solute transferred from the aqueous to the organic layer and to remove excess water from the organic layer. In our experiment, liquid-liquid extraction was performed to purify a sample of benzoic acid contaminated with salt (NaCl). Our isolated substance weighed 1.138 g, and after calculating the distribution coefficient to determine the theoretical yield of our experiment, our percentage yield was 64.95%.

Conclusion: All in all, by repeating the process of liquid-liquid extraction through incorporating principles of “oil and water don’t mix” (in that substances with varying polarities will not be miscible) and “like dissolves like” (polar molecules will dissolve in polar substances and nonpolar molecules will dissolve in nonpolar substances) we were able to purify the sample of benzoic acid. The percentage yield calculated was 64.95%. References: Works Cited (1) “Extraction (Part 1).” Extraction in Theory and Practice (Part I) , University of California, Los Angeles, 30 Dec. 2013, www.chem.ucla.edu/~bacher/Specialtopics/extraction.html. (2) Extraction . University of Pittsburg, www.pitt.edu/~ceder/lab2/extraction.html. (3) Finchsigmate, Kyle. “Liquid-Liquid Extraction.” Chemistry LibreTexts , Libretexts, 5 June 2019, chem.libretexts.org/Bookshelves/Ancillary_Materials/Demos%2C_Techniques%2C_and_Experi ments/General_Lab_Techniques/Liquid-Liquid_Extraction. (4) Liquid/Liquid Extraction . courses.chem.psu.edu/chem36/Experiments/PDF%27s_for_techniques/Liquid_Liquid.pdf....