Orgo Lab 2 - organic chem lab 2 PDF

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organic chem lab 2...

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Simona Kogan Organic Chemistry Lab 1, Section: 1 TA: Shambeda

Lab performed: 9/16/19 Report due: 9/23/19

Experiment 4B: Solvent Extraction I: Acid-Base Extraction Using the System Benzoic Acid, Methylene Chloride and Sodium Bicarbonate Solution. Objective: We will be using extraction techniques to alter the solubility (acid-base reaction) characteristics of the 2 immiscible solvents, methylene chloride and water which will help determine the partition coefficient of benzoic acid. Experimental Procedure: The procedure was followed as described in Mayo, pages 141-147, with the modifications listed in the posted Canvas document. Additional modifications to the procedure included the following: ● Use 75 mg of benzoic acid and 1.0 mL each of methylene chloride and 10% sodium bicarbonate solution. ● Use a 5-mL conical vial as in the lab textbook procedure. ● Transfer the methylene chloride layer from the conical vial using a simple glass pipet, not a filter pipet. Transfer the solution to a test tube rather than a 5-mL conical vial. ● Use anhydrous sodium sulfate instead of magnesium sulfate. ● Add a boiling stone to your vial before obtaining the tare weight ● Use a heater block to concentrate the final, dried methylene chloride solution

Reaction Scheme:

Data and Results: Benzoic Acid

Methylene Chloride

Water

10% NaHCO3 solution

Mol. Formula

C7H6O2

CH2Cl2

H2O

NaHCO3

Amount (mg)

84

Amount (mL)

83 1.00

1.00

mmoles

0.688

0.988

Molar Mass

122.13

84.01

Density (g/mL) Melting Point (C) Boiling Point (C)

1.33 122

1.00 40

1.00

Observations: ● Prior to mixing the methylene chloride, benzoic acid, and deionized water, the mixture was colorless but a little bit cloudy. You can still see the separation for extraction. ● Benzoic acid was initially a white crystal like substance but then dissolved into a clearer solution ● Top layer was clear and the bottom layer was cloudy ● The heating block rod hardened during evaporation. (Turned into a white solid very quickly) Calculations: 1. Benzoic acid in CH2Cl2 = (final weight of vial + boiling stone + solid) – (weight of vial + boiling stone) 4A:11.524-8.706=2.818grams=2818 mg 4B: 8.808-8.485=.323grams=323mg 2. Benzoic acid remaining in the aqueous layer (either water for 4A or 10% sodium bicarbonate solution

4A:83mg=323mg+x (x=-240mg) 4B:84mg=2818mg+x (x=-2734mg) 3. KpCH2Cl2/aq. NaHCO3 4A:2818mg/84mg-2818mg=-2784mg 4B: 323mg/83mg-323mg=-319mg *** Data results are off because I could have grabbed the wrong test tube or used a different beaker for the tare weight. The weights for 4A are off by about the same difference in mass between large and small test tubes therefore, this could have happened due to experimental errors. Questions: 1. a. The laboratory glass that I found to be more efficient was the separatory funnel versus the conical vial because I was able to get a more precise separation because the separatory funnel is drop by drop with more control of how much comes out. While the conical vial had a couple drops of water on the bottom which was difficult to get out. b. The most accurate piece of glassware is the separatory funnel in determining the partition coefficient because we are able to precisely release the solution drop by drop which results in limited error. This is due because we were able to get all of the organic layer out without water. This technique limits error and therefore, we are able to obtain a more accurate partition coefficient. 2. Benzoic Acid

a. b. c. d.

Circle and Label (Non Polar) London Dispersion & Dipole-induced Dipole Circle and Label (Polar) Hydrogen Bonding, Dipole-Dipole, dipole-induced dipole, and London Dispersion

e. Benzoic acid is more soluble in water then 9-fluorenone because benzoic acid is more polar than 9-fluorenone since the polar regions interact with H20 and form hydrogen bonding. “Like dissolves like”, benzoic will be more soluble. 3. a. The type of reaction that occurs is an acid-base reaction b. Sodium bicarbonate is a base in this reaction c. Draw Sodium Benzoate with charges

d. Circle and Label (Polar) e. Ion-dipole

4. a. The Kp value from Experiment A was much larger than it was in experiment 4B. b. This happened because Benzoic Acid is more soluble in methylene chloride because of Benzoic’s Acid ability to hydrogen bond to methylene chloride. Additionally, in experiment 4B neutralization occurred between the acid base reactions which resulted in less benzoic being recovered from the methylene chloride level. This is why it produced a smaller Kp value.

Works Cited: Full references for the experimental procedure(s) in the following format: 1. Mayo, D. W.; Pike, R. M.; Forbes, D. C. Microscale Organic Laboratory with Multistep and Multiscale Syntheses, 5th ed.; John Wiley & Sons, Inc., 2011; pp 141-147. 2. Modifications for Expts 4A and 4B: Partition Coefficient Part B and Solvent Extraction I, Canvas document....