PostLab Expt 4 - Chem 549-653 - 2023

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NHTI, Concord's Community College *

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Chemistry

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Feb 20, 2024

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CHEM 549/653 Post-Lab Questions Experiment 4 – Extraction (10 points) 1) a) Report the % recovery (as a % of total mass of the mixture) for all three components of the mixture used in the experiment. (Show your work) (3 points) Sucrose- (1.046/2.968g)= 0.3524*100= 35.24% Aspirin - (1.037/2.968)= 0.3480*100= 34.80% Acetanilide – (2.030/2.968)= 0.6840*100= 68.40% b) If you assume that equal amounts of the three components were in the initial mixture, provide an explanation for low recovery of the component isolated in the lowest amount. (1 point) The low recovery for the aspirin might be due to not enough HCl being added and there being too much water in the solid. 2) If sodium chloride were a fourth component in this mixture, AND the process used for the separation were unchanged, where would the sodium chloride be found? (1 point) Sodium chloride would be found in the first step because it would not dissolve with DCM. 3) The pKa of aspirin is reported to be 2.97. During the extraction process, the pH of the aqueous solution is adjusted by the addition of aqueous HCl. If one of the students in the lab lowered the pH of the solution to 2.97 and a different student used more HCl and lowered the pH to 1.0, which student would recover the greater amount of aspirin? Why? (1 point) The more HCl added will protonate and give hydrogen to the conj. base and then will yield more aspirin. 4) Comparing the experimental processes used to isolate the acetanilide and the acetylsalicyclic acid, which substance do you believe should be more pure and why? Is this result supported by the mp data? Discuss your reasoning. (1 point) Although the roto-vap is very precise, the amount of sodium sulfate that is added is variable. Adding too little sodium sulfate will result in excess water which makes it less pure. It’s whatever the student deems “not clumpy anymore,” which can sometimes be subjective.

5) If toluene (d = 0.78 g/mL) were used as the organic solvent to extract ethylene bromohydrin (d = 2.41 g/mL) from water, would the organic layer in the separatory funnel always be the top layer, the bottom layer, or could it be variable? Explain. (1 point) Ethylene bromohydrin would combine with water so it would be on the bottom in the first round because it would have a greater density, and toluene would be on the top. But the toluene and Ethylene bromohydrin would both be on the bottom and water would be on the top in the second filtration, so you would have to repeat this process a few times to separate them. 6) How would you determine which layer was the organic layer and which was the aqueous layer? (1 point) The organic layer is on the bottom, and the aqueous is on the top in this experiment, but it mainly depends on the density of the solvents and the products. 7) In the drying process of the acetanilide containing solution, you were provided guidance for determining the correct amount of drying agent to use. What would be the consequence of not using enough drying agent? What would be the consequence of using too much? (1 point) Adding too little will result in too much water. Adding too much will result in making filtration difficult.

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