Lab 3 - Extraction PDF

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Summary

Extraction Separation of p-dimethoxybenzene and benzoic acid by extraction...

Description

EXTRACTION – LAB 3 Johanna Mead (Lab partner: Dyan Cruz) Professor Rajendra Shakya Ph.D Date of experiment: January 29, 2019

PURPOSE

The purpose of these experiments is to accomplish the following: 

To become familiar with the equipment and apparatus used to perform extraction in the laboratory.



To understand that a substance can be selectively transferred between phases to allow it’s extraction from one phase to another in order to separate it or purify the original substance

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To realize that the property of immiscibility is useful because polar solutes will primarily dissolve in polar solvents and non-polar solutes will primarily dissolve in non-polar solvents. Each compound has a specific solubility of how much it will dissolve when placed in 100mL of a solvent. This allows for the calculation of the distribution coefficient as a ratio of these two numbers can be calculated.

INTRODUCTION

Extraction is a process of removal. Extraction in everyday life includes being able to extract the flavor of tea from tea leaves when they are placed in water, coffee from coffee grounds and the even the flavor of vanilla pods into vodka. In organic chemistry, extraction is an important technique used to separate compounds from a mixture of compounds or to remove impurities from a single compound. It relies on the Theory of Extraction. When a solute is in the two immiscible liquids it will favor the phase that is most close to it in polarity, but some of the solute will also be dissolved slightly in the other phase that it does not favor. This ratio of solubility in the two immiscible solvent is called a distribution coefficient. Because the distribution coefficient is constant it is important to

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EXTRACTION – LAB 3

perform batch extraction. This will allow more and more of the solute to be able to transfer into the solvent as the same ratio of solute will be transferred each time. Each time the ratio of solute in the two immiscible phases will be the same and each time just a little bit more of the solute will be recovered and less and less will remain in the non-favored phase. Due to the different physical properties of compounds it is possible to set up experiments where it is known which compound will dissolve into which solution. A polar solid solute will dissolve in a polar solvent and a non-polar solute will dissolve in a non-polar solvent.

A common technique used in the organic chemistry laboratory is a liquid-liquid extraction. It sounds strange that two liquids can be used in this way as liquids usually mix together. However, providing that the two liquids being used are immiscible and do not mix, then a liquid-liquid extraction can be performed and the two liquids will form layers when placed into a glass, or in the organic laboratory, a separatory funnel. The two liquids form layers because they have different polarity. Usually one phase (liquid) will be polar and one phase will be non-polar. One layer will form on the top and one on the bottom. The layer with the greatest density will be the bottom layer. If you do know which layer is the aqueous layer and which is the organic layer then you can take a few drops of one of the layers and place in a test tube that contains water. If the layer is the organic layer then it will not mix with the water and if it is the aqueous layer then it will mix with the water. In this way the two layers can be separated and the solute can be transferred from one liquid to another until the compounds have been separated or the impurities removed. In this experiment the initial solvent used to dissolve the mixture of Benzoic Acid and Dimethoxybenzene was diethyl ether. It is an organic solvent that is relatively inert and does not react with solute and has a low boiling point which allows it to be removed easily. Another reason that ether was chosen as the initial solvent was because the extraction mixture would produce an aqueous phase and as ether is less dense than water it, would be the top layer and the aqueous layer could easily be drained and collected after each successive extraction.

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EXTRACTION – LAB 3 MATERIALS 250mL Erlenmeyer flasks

Graduated glass cylinders

50mL glass beakers

100mL glass beaker

50mL Erlenmeyer flasks

Hot plate

Separatory Funnel

Glass Funnel

Clamp Stand

Clamp

Spatula

Glass Rod

Thick walled tubing Ice Balance

PROCEDURE 

Set up clamp stand and clamp

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Placed separatory funnel in clamp add glass stopper

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Measured 1 gram of Benzoic Acid and Dimethoxybenzene mixture

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Added to 125mL Erlenmeyer flask

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Measured 45mL of ether into a graduated cylinder cool in ice bath

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Added Ether slowly to dissolve the solid mixture

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Made sure that the stopcock is in the closed position on separatory flask

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Added Ether and dissolved solid to the separatory flask, replace glass stopper

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Shuck with stopcock pointed up and away from you and others

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Opened stopcock to release pressure (repeat shake and release 2 more times)

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Measured 10mL of 0.5M NaOH add to separatory flask

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Shuck with stopcock pointed up and away from you and others

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Opened stopcock to release pressure

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Allowed layers to separate

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Removed glass stopper and drain bottom aqueous layer into a 125mL Erlenmeyer flask labelled ‘Aqueous’

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Measured another 10mL of 0.5M NaOH and repeat shake and release

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EXTRACTION – LAB 3

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Removed glass stopper and drain bottom layer to flask layered ‘Aqueous’

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Measured 10mL of cool H₂O to separatory flask and repeat shake and release

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Removed glass stopper and drain bottom layer to flask layered ‘Aqueous’ and set aside

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Poured the remaining Ether layer from the top of the flask into a 125mL Erlenmeyer flask labelled ‘Org’

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Measured 1.0g of Na₂SO₄ add to flask labelled ‘Org’ add stopper and set aside

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Washed the separatory funnel with water

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Poured the solution from the flask labelled ‘Aqueous’ into the separatory funnel

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Added 5mL of cooled HCl

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Used pH paper check the pH is acidic

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Measured 30mL of Methylene Chloride

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Added 10mL at a time and perform a successive extraction saving the clear drained solution in clean a 125mL Ehrlenmeyer labelled ‘Aqueous’

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Added a drying agent, MgSO₄ to the extraction.

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Placed the flask labelled ‘Aqueous’ in hot water bath under vent hood and waited for evaporation of water to occur.

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Placed the flask labelled ‘Org’ into the water bath also.

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Removed the dimethyoxybenzene from the water bath when just a small amount of liquid is left. Allowed to cool and crystals formed.

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Removed Benzoic acid when crystals formed.

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Weighed both in Erlenmeyer flask and recorded weights

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Used Mel-temp machine to find out melting point ranges of both substances.

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EXTRACTION – LAB 3 SKETCH OF EXPERIMENT SET UP

TABLE OF REAGENTS

Name Benzoic Acid p Dimenthoxybenzene Diethyl Ether Sodium Hydroxide Hydrochloric Acid Methylene Chloride Anhydrous Magnesium Sufate Anhydrous Sodium Sulfate

Table of Reagents Formulas Molecular Weight C₇H₆O₂ 122.12g/mol C₆H₄(OCH₃)₂ 138.17g/mol C₂H₆O 46.07g/mol NaOH 39.99g/mol CH₃COOH 36.46g/mol CH₂Cl₂ 84.93g/mol

Melting Boiling Point Point 122°C 249.2°C 55°C 212°C 55°C 212°C °C 114.3°C °C °C °C °C

Density 1.27g/cmᴲ 790kg/mᴲ 2.11kg/mᴲ 1.22g/cmᴲ 1.64g/L 1.33g/cmᴲ

MgO₄S

120.37g/mol

°C

°C

2.45g/cmᴲ

Na₂SO₄

142.04g/mol

°C

°C

2.66g/cmᴲ

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EXTRACTION – LAB 3 DATA AND OBSERVATIONS

COMPOUND Benzoic Acid pDimenthoxybenzene

WEIGHT 0.692g 0.531g

TEMPERATURE WHEN Sample begins Sample completely to melt melted 115°C 120.3°C 25.4°C 50.4°C

OBSERVATIONS Lower layer Upper layer

Total recovery of the two compounds = 0.692g + 0.531g = 1.223g % Yield = Actual yield x 100% Theoretical yield

1.223g x100% = 121.69% 1.005g

DISCUSSION

When dissolved in the ether the mixture became clear. During the shake and release stage the initial release made a noise like a soda can being opened when it had been very slightly shaken. The second time that the stopcock was opened the pressure was less, but there was still a slight ‘shh’ noise. The third time there was no noise and almost imperceptible amount of pressure being released. When the NaOH was added to the separatory funnel the layers were both clear liquids, but there was still a distinct layer separation that could be seen. It was surprising that two clear liquids could show a layer separation if they were immiscible with each other, but they did. A white precipitate formed in the aqueous layer solution immediately when the 5mL of HCl was added. Later in the process the Anhydrous magnesium sulfate became opaque and solid immediately when it was added to the benzoic acid in methylene chloride. Similarly, when the anhydrous sodium sulfate was added to the p-dimethoxybenzene, the powder became quite solid as it attracted the water out of the solution. It became quite hard and crystalline. During the evaporation stage when the two solutions were being heated in the water bath only one solution, the benzoic acid, crystallized when being heated. The pdimethoxybenzene remained in a liquid phase. Due to its low melting point it needed to be added to an ice bath to allow the compound to cool and get to a point below its melting point, then the solid p-dimethoxybenzene began to form. 6

EXTRACTION – LAB 3 Our percentage yield was more than 100%. We had a 20% increase in the weight of our recovered substances when we added them together. Also, the melting point of pure Benzoic acid is 122°C and our sample began to melt at 115°C and was completely melted at 120.3°C indicating that it was close, but not completely pure. The melting point of Dimethypoxybenzene is 59°C and our sample had a wide range for its melting point from 25.4°C-50.4°C again indicating that the sample was contaminated still. The possible reason for the 20% increase could be caused by thee small Erlenmeyer flask used to weigh the samples not being completely dry and water vapor was still inside the flasks, or that the samples themselves were not completely dry and this could reflect a higher weight and influence the mass measured.

CONCLUSION The fundamental reason for carrying out an extraction is to isolate a compound from a mixture. In this experiment we had one polar compound Benzoic Acid and one and one nonpolar compound p-dmethoxybenzene. We had a polar solvent, water and a non-polar solvent, ether. After extraction with the solvent pair of ether and water, the polar compound would be in the aqueous layer and the non-polar compound would be in the ether layer. It is possible to separate compounds from mixture if their physical properties are known. By knowing the physical properties of compounds it is possible to use theory of extraction and the distribution coefficient Kd Extractions are performed in a separatory funnel. When two immiscible liquids are placed in the separatory funnel two phases are observed. As a result the polar and non-polar compounds have been isolated from the mixture. Like dissolves like is often used to remind us that compounds of similar polarity are able to dissolve in each other. However, there is often a little of the solute in the opposite polarity phase, although not much. The idea that a compound dissolves in a solvent can be explained using the distribution coefficient, which states that there is a ratio of the concentration of the solute between the two phases given the solvent pair and temperature. POST-LAB QUESTIONS

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EXTRACTION – LAB 3 1. Why would ethyl alcohol not be a good solvent to use with water in an extraction? Ethyl alcohol is polar and so is water so they would not create separate layers and they would mix together as they are homogenous. 2. How does the extraction procedure differ when the organic phase is a) less dense than water and b) more dense than water? What differences did you observe between the two drying agents that you used today? When the organic phase is less dense than water it will be the top layer and it will need to be removed from the separatory funnel from the top. When the organic phase is denser than water it will be the bottom layer and will be removed using gravity and the stopcock. The magnesium sulfate is an acidic salt and the Sodium sulfate is a neutral salt.. When the magnesium sulfate was added to the Benzoic acid it looked like oil was in the flask so more was needed to be added to adequately dry the benzoic acid. When the Sodium sulfate was added to the p-Dimenthyoxybenzene it formed an opaque solid in the flask that did not easily move when the flask was shaken. 3. What is the purpose of venting the separatory funnel by occasionally opening the stopcock during the shaking process? Why is there a buildup of pressure even when no gas is being produced by a chemical reaction? The ether is volatile and will move between the liquid and gas phase easily. It will create a slight buildup of pressure in the separatory funnel when they are shaken. It is necessary to release the ether vapor so that the glass not break. 4. What is the biggest safety hazard in this equipment? The biggest safety hazard whilst preparing an extraction in the organic chemistry laboratory is the handling of chemicals and the potential for breaking glass. 5. Describe a procedure that might be used to separate p-dichorobenzene (a neutral compound) from p-chloroaniline (a basic compound) by extraction? p-chloroaniline is soluble in warm water as it is polar and is water. p-dichloronezene is not soluble in warm water it is non-polar and insoluble. If the mixture is placed in warm water the p-chloroaniline would dissolve in the water and become and aqueous solution that could be separated from the solid p-dichloronezene. 6. Why is it necessary to remove the stopper from the separatory funnel when the liquid is being drained through the stopcock? If the stopper is not removed when the liquid is being drained from the separatory funnel then the liquid will not drain as a vacuum will be formed. The liquid that is being drained needs to be replaced in the separatory funnel by air to allow an equilibrium in pressure to allow gravity to pull the liquid towards it.

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