Acid-Base Liquid-Liquid Extraction Writer Draft PDF

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Acid-Base Liquid-Liquid Extraction Organic Chemistry 236 Lab 15th March 2021 Writer: Mohammed Ghalib Reviewer: Laila Hancock Editor: Sharon Gallegos

Introduction

Liquid-liquid extraction is used to separate organic compounds from a mixture of compounds. In this technique, two solvents that differ in polarity are added to a separatory funnel. This results in the formation of an aqueous layer and an organic layer which are immiscible due to the difference in their polarity. The solvents can easily be separated due to the formation of two immiscible layers. [1] Acid-base extraction is used when a nonpolar organic compound has the potential to exhibit bronsted lowry acid or base properties. The compound is made more polar due to an acid-base reaction and is thus easily miscible with a polar solvent. This polar solvent can be easily extracted from the mixture. A neutralization reaction done on the polar compound which results in the charge being removed and we get our initial nonpolar organic compound. [2] The main difference between the two extraction techniques is that a difference in polarity is created in acid-base extraction via adding a strong Acid or strong Base to the mixture, whereas Liquid-liquid extraction is used when a difference in polarity already exists between the two compounds. Like-dissolves-like refers to the phenomenon by which polar substances dissolve in polar substances, non-polar substances dissolve in non-polar substances. Furthermore, non-polar substances are immiscible with respect to polar substances [3]. Polar substances refer to compounds with ionic bonds or hydrogen bonding. The majority of organic compounds are nonpolar and exhibit Londondispersion forces. In Liquid-liquid extraction, we identify two compounds that are not “like” ie. differ in polarity and use solvents that are “like” to extract them. In acid-base extraction, we are given two nonpolar organic compounds and we make one of them polar to complete our extraction. Acid-base extractions can be used to separate acidic, basic, and neutral compounds by protonating or deprotonating an organic compound via adding a strong Acid or strong Base respectively. Since the previously non-polar compound turns into its polar conjugate acid/base self, we can use a polar solvent to extract it.

Table of Reagents

Compound

Molecular Weight (g/mol) Melting Point (°C)

Boiling Point (°C)

Density (g/cm3)

Water

18.01

0

100

1

HCl

36.46

-114.2

-85.05

1.1

NaOH

39.9

318

1388

2.13

Mixture 1 Compound

165.192

88-90

310

n/a

Mixture 2 Compound

197.119

242

n/a

n/a

Common Compound

195.03

55-58

182

n/a

Sudan Orange

214.22

144

407.5

1.24

Sudan Blue

342.4

121

538.6

1.3

Hexane

86.18

-95.3

69

0.66

Experimental Week 1 Procedure To begin the experiment, 6 mL of the Sudan Orange standard in hexane was obtained. approximately 2 mL of the standard was added to each of three separate test tubes. 2ml of HCl was added to the first test tube, 2 ml of Water were added to the second test tube, and 2 ml of NaOH was added to the third test tube. Each test tube was capped and shaked which resulted in the formation of two distinct layers. The procedure was repeated with the sudan blue solution. 10 ml of a mixture of Sudan Blue and Sudan Orange dissolved in hexane was added to a separatory funnel. 10 ml of NaOH was added for each extraction which was performed three times and the bottom layer was collected in a beaker. The extraction was performed by holding the stopper in place with one hand, inverting and swirling the separatory funnel allowing for the liquids to get mixed. The separatory funnel was vented to release built-up pressure by holding the stopper in place and inverting the funnel, opening the stopcock facing upward and into the hood. The stopcock was closed and the process of inverting and swirling

was repeated, followed by venting, several times. An iron ring was secured onto a stand and the funnel was placed securely into the ring. The separatory funnel was allowed to sit until the two layers were completely separated. A clean beaker was placed below the funnel, the stopper was removed, and the stopcock was opened, slowly draining the bottom layer out into a beaker. When the bottom layer was nearly removed, the draining rate was slowed down to make sure that the top layer did not enter the beaker.

Week 2 Procedure To begin the experiment, 15 ml of Mixture 2 solution was placed in a 125 ml separatory funnel. Since one of the compounds in the mixture was an acid, 10 ml of NaOH were added which deprotonated the compound. The solution was shaken and 2 distinct layers formed. The compound was extracted and this was repeated thrice, with NaOH added each time. The aqueous solution was collected in a 200 ml beaker. 1M HCl was added to the beaker to neutralize the compound. The neutralization was done by regularly testing with litmus paper in between additions of HCl. Once the litmus paper tested as red/acid, the solution was stirred and a solid formed. The solid was isolated via suction filtration and weighed. Meanwhile, our organic layer was added to a 50 ml erlenmeyer flask and ‘dried’ by adding sodium sulfate. Sodium sulfate was added until it stopped clumping. This ‘dried’ solution was transferred to another 50 ml flask, leaving the sodium sulfate behind. The solution was indirectly heated via a water bath set to 40-50 C. The solid left after the ethyl evaporated was collected and weighed. Both of the layers were also retained for melting point analysis.

Results Week 1 Results Solubility of Sudan Orange and Sudan Blue at Different pH Levels Compound

1M HCl

Distilled Water

1M NaOH

Sudan Orange

Insoluble (hexane) Insoluble (hexane) Soluble (aqueous)

Sudan Blue

Insoluble (hexane) Insoluble (hexane) Insoluble (hexane)

When the mixture of Sudan Blue and Sudan Orange was added alongside NaOH into a separatory funnel, the NaOH sank to the bottom and was slightly tinged yellow. After inverting and swirling, the top of the funnel was bright blue (hexane) and the bottom of the funnel was dark yellow/ orange-ish in color (NaOH). Extraction was performed three times. The second extraction was similar to the first one. The final extraction had a pale yellow color. Week 2 Results Percent Yield Analysis: Organic Layer solid Percent Yield = 15.33% Aqueous Layer solid Percent Yield = 39.33% [The calculation was as follows: Percent Yield = (0.023/0.15) * 100% = 15.33%] Melting Point Analysis: Organic Layer Measured Melting point = 55.2 °C Aqueous Layer Measured Melting point = 240.2 °C

Discussion Week 1 Discussion

Sudan Blue

Sudan Orange

Sudan Orange Conj. Base

Since only Sudan Orange was soluble in NaOH in part 1 of our experiment and the rest of the dyes were not soluble in any other solvent, we chose NaOH as our aqueous solution for the extraction. Because NaOH shared a similar polarity with Sudan Orange, it was easy to separate the Sudan orange from the Sudan blue. The Sudan orange dye underwent a deprotonation state by the NaOH. When NaOH was first added to the separatory funnel, it only took up a slight tinge of yellow color but once we inverted and swirled it around, it took up a deep yellow color. This indicated to us that we chose the correct aqueous solution. Right before draining the final extraction,the bottom layer had a pale yellow color indicating that most of the sudan orange had been extracted.

Week 2 Discussion

Because the compound originally present in the mixture was an acid, NaOH was chosen as the aqueous solvent. The compound underwent deprotonation and became its conjugate base in the presence of NaOH. 1M HCl was used as the neutralizing agent for the conjugate base as it would be able to neutralize the solution. This experiment was prone to errors due to possible contamination between layers where not all the aqueous and organic layers were separated.

Conclusion This experiment applied acid-base liquid liquid extraction to separate two distinct compounds by their property to be miscible in a solvent with similar polarity (like-dissolves-like) as discussed in the introduction. By applying Bronsted Lowry acid-base theory we were able to change one of the compound’s acidity/basicity which also changed their polarity and separated the mixture into an aqueous layer and an organic layer. Both filtration and evaporation were performed to separate the solid filtrates in each layer. Through this experiment, we determined that Sudan orange is only soluble in substances with a basic pH. Furthermore, the melting points of both solids were obtained in week 2. The aqueous layer had a melting point of 240.2 ℃. The organic layer had a melting point of 55.2 ℃. These melting points were very similar to the melting points listed in the Lab Procedure and thus the solids we obtained could be considered pure. This lab experiment can be improved by utilizing many different compounds for the purpose of extraction. Using compounds that were similar in polarity and thus soluble in each other would allow us to observe different types of results. Another improvement would be making us repeat the extraction many times to see at what point is the extraction truly complete.

References [1] Acid-Base Liquid-Liquid Extraction Background Week 1 Acid-Base Liquid-Liquid Extraction Background-Week 1.pdf: SP2021 CH 236 Organic Chemistry I Lab (instructure.com)

[2] Acid-Base Liquid-Liquid Extraction Background Week 2 Acid-Base Liquid-Liquid Extraction Background-Week 2.pdf: SP2021 CH 236 Organic Chemistry I Lab (instructure.com) [3] Like dissolves like Primary Connections: Linking science with literacy...