Acid-Base Liquid-Liquid Extraction Final Draft PDF

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Using Acid-Base Liquid-Liquid Extraction to Separate Organic Compounds

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Introduction Liquid – Liquid extraction is a technique used to pull a compound from solvent A to solvent B where A and B are immiscible. This is typically performed while using a separatory funnel.1 When in the separatory funnel, the two solvents will form an “organic” and an2 “aqueous” layer. The more dense layer will be on the bottom of the funnel, while the less dense2 layer will be on the top. Forming two layers achieves the goal of one layer being able to be2 removed and thus allowing the extraction of the desired compound. Acid-Base is a sub-category of liquid-liquid extraction. It involves an organic solvent that typically does not dissolve well in water.3 Substances that donate protons (H +) are known as Bronsted-Lowry acids and the2 substance that accepts the protons from the acids are known as Bronsted-Lowry bases. “Like-dissolves-like” is a concept that states that compounds of similar composition will dissolve in the same relative solvent such as polar compounds will dissolve in polar solvents and nonpolar compounds will dissolve in other non-polar solvents.2 During liquid-liquid extractions, the desired result of being able to separate two separate layers would not be able to be achieved if following the rule of “like-dissolves-like.” When this principle is used, it forms one single layer instead of two due to similar polarities dissolving in one another.2 Therefore, when performing liquid-liquid and acid-base extractions, one needs to use solvents that are distinctly different in polarity for the desired result to be achieved.2 During acid-base extractions, Bronsted-Lowry acids become more negatively charged while Bronsted-Lowry bases become more positively charged.2 By adding charge to the molecules, they become more polar and thus able to dissolve in polar (aqueous) solvents. If sites on the molecules act as Bronsted-Lowry acids, Bronsted-Lowry bases can be used to deprotonate the molecule thus making its charge more negative and more soluble in the polar phase. If sites on the molecules act as Bronsted-Lowry bases, Bronsted-Lowry acids will protonate the substances thus making it more positive and more soluble in the polar phase.2 When compounds are neutral, meaning that they are neither Bronsted-Lowry acids or bases, they will remain in the non-polar solvent throughout the acid-base liquid-liquid extraction.2 At some point, compounds in the aqueous polar phase may need to be isolated and thus need to be neutralized. Bronsted-Lowry bases can be added to remove protons making the substances non-polar thus being able to separate from the water and be isolated. Negatively charged compounds can be removed from water by addition of Bronsted-Lowry acids thus making the substance also nonpolar.2

Table 1: Table of Reagents – Week One Compound Name

Molecular Weight (g/mol)

Melting Point ( !C)

Boiling Point ( C) !

Density (g/mL)

Hexane4

86.18

-95.3

68.7

0.66

HCl5

36.46

-114.2

-85.05

1.19

Distilled Water6

18.02

0

100

1.0

NaOH7

39.99

318

1388

2.13

Sudan Orange8

214.22

145 – 146

407.50

1.24

Sudan Blue9

350.45

120 – 122

568.7

1.18

Table 2: Table of Reagents - Week Two Compounds

Molar Mass

Melting Point

Boiling Point

165.192

88-90

310

195.053

55-58

182

197.119

242

N/A

Experimental To begin the week 1 part 1 experiment, 6 mL of Sudan Orange standard in Hexane was obtained. Approximately 2 mL of Sudan Orange was added to three separate test tubes. To one test tube, approximately 2 mL of the 1 M HCl solution was added. To another test tube, approximately 2 mL of distilled water was added. To the third test tube, approximately 2 mL of 1 M NaOH solution was added. The relative location of the hexane standard and aqueous layers was noted. The test tubes were then capped and shaken which allowed the layers to separate. The final location of the Sudan Orange after agitation was then noted. The experiment above was then repeated with Sudan Blue. 6 mL of Sudan Blue standard in Hexane was obtained. Approximately 2 mL of Sudan Blue was added to three separate test tubes. To one test tube, approximately 2 mL of the 1 M HCl solution was added. To another test tube, approximately 2 mL of distilled water was added. To the third test tube, approximately 2 mL of 1 M NaOH solution was added. The relative location of the hexane standard and aqueous layers was noted. The test tubes were then capped and shaken which allowed the layers to separate. The final location of the Sudan Blue after agitation was then noted. Part 2 of week 1 was started by obtaining a standard solution of a mixture of Sudan Blue and Sudan Orange dissolved in Hexane. Based on the results from part one of the lab, one aqueous solution of 1M NaOH was selected to separate out the colored compound into the aqueous solution, leaving the Sudan blue in the hexane standard. An extraction was then run on the 1M NaOH by first obtaining 25 mL of the Sudan Blue, Sudan Orange dye mixture and 45 mL of the selected aqueous solution. The stopcock was then closed, and 25 mL of the dye mixture was added to a 125 mL separatory funnel. The color of the dye was noted.

15 mL of the 1M NaOH was added to the separatory funnel. Holding the stopper in place with one hand, the separatory funnel was inverted and swirled allowing for the liquids to mix. The separatory funnel was vented every few inversions by opening the stop cock and pointing the separatory funnel away from others. The stopcock was then closed, and the process of inverting and venting was repeated several times. An iron ring was secured on a ring stand and the funnel was placed securely into the ring. The separatory funnel was then allowed to sit until the two layers completely separated. A clean beaker was then placed below the funnel, the stopper was removed, the stopcock was opened, and the bottom layer was slowly drained into the beaker making sure to stop before any of the top layer was drained into the beaker. The colors in the beaker and funnel were inspected and compared to the standards analyzed in part 1. The same extraction process was repeated two more times each with 15 mL of the 1M NaOH solution. To begin week 2 part 1 of the lab, 15 mL of the assigned mixture number 1 was obtained. The mixture solution was placed into a 125 mL separatory funnel. The compound was extracted 3 times with 10 mL of the selected aqueous solution from week 1, and the aqueous solution was collected in a 200 mL beaker. The separation scheme was then used to determine which compounds were in which layer, and the protonation state of each compound.

Figure 1. The two molecules that were dissolved in hexane in assigned mixture number one.

For week 2 part 2, 1M NaOH was selected to neutralize the extraction solution. The selected solution of 1M HCl was added and pH was checked using litmus paper to ensure that neutralization occurred. HCl was added until the solution was acidic or basic. At this point, a solid formed in the beaker and remained undissolved in the solution. The solid was then isolated through suction filtration and dried by pulling air through the solid by suction filtration. The solid was then collected, weighed for percent yield calculations, and retained for further analysis. Next, diethyl ether was dried through addition of anhydrous sodium sulfate. To dry the organic layer, the diethyl ether solution was added to a 50 mL Erlenmeyer flask, and sodium sulfate was added a little at a time. The sodium sulfate was added until the amount of solid flowed freely at the bottom when the flask was swirled. The liquid was transferred to a clean 50 mL beaker leaving the sodium sulfate behind in the other beaker. A hot water bath was gently heated to 40 – 50 C. ! The beaker with the ether solution was placed into the hot water bath and the ether was gently boiled off until the liquid was completely removed. The beaker was removed from the hot water bath and allowed to cool

to room temperature to reform the solid. The solid was then collected, weighed for percent-yield calculations, and retained for the melting point analysis. The purity was analyzed by determining the melting point of each. Everything was then disposed of properly.

Results Table 3: Solubility of Sudan Orange and Sudan Blue at Different pH Levels Compound

1M HCl

Distilled Water

1M NaOH

Sudan Orange

Hexane (insoluble)

Hexane (insoluble)

Aqueous (soluble)

Sudan Blue

Hexane (insoluble)

Hexane (insoluble)

Hexane (insoluble)

Before the extraction procedure during week 1, the Sudan orange/Sudan blue mixture was a deep teal/green color. Distilled water, 1M HCl, and 1M NaOH were all transparent before the extraction procedure. After the three extractions of 1M HCl, HCl in the beaker was a creamy/light-yellow color. Following the extraction of distilled water, the transparency of the water remained unchanged. Lastly, after the extractions of 1M NaOH, NaOH appeared deep yellow in color.

Table 4: Data of Solids Obtained from the Aqueous and Organic Layers Layer

Weight (g)

Percent Yield (%)

Melting Point ( ! C)

Aqueous

0.066

44%

93.3 – 95.5

Organic

0.126

84%

54 – 56

The calculation for percent yield is as follows: Percent yield = (actual yield / theoretical yield) x 100.10 Percent yield calculation for Aqueous layer: .126g (actual)/.15g (theoretical) = .84 x 100 = 84%

Discussion In the week one extraction, 1M NaOH was chosen as the aqueous solution because it is immiscible with hexane and shared a similar polarity with Sudan Orange as seen in Table 3 above. Because of NaOH sharing 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 and its state as a conjugate base after deprotonation is shown below.

Figure 2: Sudan Orange

Figure 3: Sudan Blue

Figure 4: Sodium Hydroxide

Figure 5: Hexane

Figure 6: Conjugate Base of Sudan Orange

Because the compound originally present in the mixture was basic, HCl was chosen as the aqueous solvent during week two of the lab. The compound became protonated into its conjugate acid in the presence of HCl. 1M NaOH was selected as the neutralizing agent for the conjugate acid because it is a strong base. This experiment was prone to errors due to possible contamination between layers where not all the aqueous and organic layers were separated.

Figure 7: Diethyl Ether

Figure 8: Hydrochloric Acid

Figure 9: Conjugate Acid

Figure 10: Molecule after NaOH Addition

Conclusion This experiment applied acid-base liquid liquid extraction to separate two distinct compounds by their ability to dissolve in a solvent similar in polarity. The Bronsted Lowry acidbase theory2 was utilized to manipulate one of the compound’s acidity/basicity which further separated the mixture into an aqueous layer and an organic layer. Two systems, filtration and evaporation, were then performed to obtain the solid filtrates of each layer. Through this experiment, it was determined that Sudan orange is only soluble in substances with higher pH. Furthermore, the melting points of both solids were obtained. The aqueous layer had a melting point of around 93.3-95.5 ℃ and 0.66 grams of solid was collected. The organic layer had a melting point of around 54-56 ℃ and 0.126 grams of solid was collected. This lab experiment could be improved by utilizing multiple different compounds to run the experiment. Using compounds that were miscible with each other would allow students to compare how each one reacts. Performing multiple extractions would also be a beneficial way to optimize this experiment and eliminate any impurities.

References 1. Liquid-Liquid Extraction. https://chem.libretexts.org/Courses/Bethune-Cookman_University/B-CU%3A_CH 345_Quantitative_Analysis/CH345_Labs/Demonstrations_and_Techniques/General_Lab _Techniques/Liquid-Liquid_Extraction (accessed July 15, 2020). 2. Acid-Base Liquid-Liquid Extraction Procedure. https://uab.instructure.com/courses/1527297/ 9 (accessed July 17, 2020). 3. Acid-Base Extraction. https://chem.libretexts.org/Bookshelves/Ancillary_Materials/Demos%2C_Techniques%2 C_and_Experiments/General_Lab_Techniques/Acid-Base_Extraction (accessed July 15, 2020). 4. Hexane. https://pubchem.ncbi.nlm.nih.gov/compound/Hexane (Links to an externa (accessed July 15, 2020).

l site.)

5. Hydrochloric Acid. https://pubchem.ncbi.nlm.nih.gov/compound/Hydrochloric-acid (Links t o an external site.) (accessed July 15, 2020). 6. Distilled Water. https://pubchem.ncbi.nlm.nih.gov/compound/Water (Links to an externa l site.) (accessed July 15, 2020).

7. Sodium Hydroxide. https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-hydroxide (Links t o an external site.) (accessed July 15, 2020). 8. Sudan Orange. https://pubchem.ncbi.nlm.nih.gov/compound/Sudan-orange (Links to a n external site.) (accessed July 15, 2020). 9. Sudan Blue. https://pubchem.ncbi.nlm.nih.gov/compound/Sudan-blue (Links to an externa l site.) (accessed July 15, 2020). 10. Percent Yield. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory _Chemistry_(CK-12)/12%3A_Stoichiometry/12.9%3A_Theoretical_Yield_and_Percent_ Yield...