CHEM 2152 Lecture Notes - Lecture 6: Diethyl Ether, Sodium Sulfate

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CHEMISTRY 2153

ACID AND BASE EXTRACTION - EXERCISE ANSWERS

2. The anhydrous sodium sulfate is used to remove the last traces of water that may remain in the organic solvent.

Although the organic solvent was chosen because it is "immiscible" in water, it is generally the case that the two liquids will

have some slight solubility in each other. For example, the solubility of ether in water is 6 g/100mL and of water in ether is

1.2 g/100mL at 25°.

3. Swirling increases the surface area of contact between the solution and the drying agent. This process hastens the

drying.

5. We use the equation x mL water

K = ------ X ----------------------

a - x mL diethyl ether

Part a.

x 400

3.0 = --------- X --------- Solving x = 7.2 g

12 - x 200

Part b.

For the first extraction with 67 mL:

3.0 = [x/(12-x)] X 400/67 , Solving x= 4.01 g

For the second extraction with 67 mL

3.0 = [x/(12-4.01-x)] x 400/67, Solving x= 2.67 g

For the third extraction with 67 mL

3.0 = [x/(12-4.01-2.67-x)] X 400/67, Solving x= 1.78 g

Total extracted = 4.01 + 2.67 + 1.78 = 8.46 g

Thus, three extractions with the same total volume of extracting solvent are more efficient than a single extraction.

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Document Summary

The anhydrous sodium sulfate is used to remove the last traces of water that may remain in the organic solvent. Although the organic solvent was chosen because it is immiscible in water, it is generally the case that the two liquids will have some slight solubility in each other. For example, the solubility of ether in water is 6 g/100ml and of water in ether is. Swirling increases the surface area of contact between the solution and the drying agent. This process hastens the drying. x ml water. K = ------ x ---------------------- a - x ml diethyl ether. 3. 0 = --------- x --------- solving x = 7. 2 g. 3. 0 = [x/(12-x)] x 400/67 , solving x= 4. 01 g. 3. 0 = [x/(12-4. 01-x)] x 400/67, solving x= 2. 67 g. 3. 0 = [x/(12-4. 01-2. 67-x)] x 400/67, solving x= 1. 78 g. Total extracted = 4. 01 + 2. 67 + 1. 78 = 8. 46 g.

Related Questions

Organic chemistry question about extraction lab...?
Procedure:
Place 2.0 g of the mixture of sucrose, acetylsalicylic acid and acetanilide into a 125 mL Erlenmeyer flask.
Add 50 mL of methylene chloride (dichloromethane) and dissolve as much of the solid as possible.
Remove the insoluble sucrose via gravity filtration using fluted filter paper. Allow to dry until the next lab period.
Add the methylene chloride solution to the separatory funnel and extract it with two 25 mL portions of 5 % sodium bicarbonate (aqueous).
Place the combined aqueous layers into a 400 mL beaker and add enough concentrated hydrochloric acid to make it very acidic (less than pH of 2) â approximately 10 mL
Allow the solid to crystallize from the aqueous layer. Chilling in an ice bath may be required.
When lots of solid has been formed, collect the solid by vacuum filtration. Wash the solid with approximately 5 mL of cold water
Allow the solid to dry open until the next lab period.
Dry the organic layer (methylene chloride) over anhydrous sodium sulfate.
Decant the solvent from the drying agent (or gravity filter through fluted filter paper) into a clean, dry a pre-weighed 100 mL round-bottom flask.
Evaporate the solvent using rotary evaporation and allow the residue to dry open over the week.
The following lab period, weigh all 3 solids, take the melting points of all 3 solids and calculate the percent composition of the original solid.

Drying agents:
Equations for drying agents:
MgSO4 (s) + 7 H2O(l) ï MgSO4.7H2O(s)
CaSO4(s) + 2 H2O(l) ï CaSO4.2H2O(s)
CaCl2(s) + 6 H2O(l) ï CaCl2.6H2O(s)
Na2SO4(s) + 7 H2O(l) ï Na2SO4.7H2O(s)

1. The original organic solution was extracted two times with aqueous sodium bicarbonate. After the extraction, what compound(s) were in the organic layer? What compound(s) were in the aqueous layer?

________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Assume that both acetylsalicylic acid and acetanilide are soluble in diethyl ether, and that diethyl ether was used in place of the methylene chloride. Would the ether layer be the bottom layer in the separatory funnel or the top layer? Explain your answer.

3. Assume that both acetylsalicylic acid and acetanilide are soluble in methanol, and that methanol was used in place of the methylene chloride. What problem(s) might occur during the extractions? (Careful, this is a trick question.)

4. Historically, the solid residue that is left after the methylene chloride solution is evaporated has a lower melting point that its literature value, due to impurities. Explain what impurities are present and why.

Please help me with the following problem. It has many parts to it, but it is one question. Thank you in advance

Synthesis of 1-Bromobutane

Reaction Scheme

NaBr, H2SO4

CH3CH2CH2CH2OH---------------------> CH3CH2CH2CH2Br + NaHSO4 + H2O

H2O

Possible by-products:

1-butene (bp â6.3 ^oC), di-n-butyl ether, C₄H₉OC₄H₉, (bp 141 ^oC)

Properties of reagents and product:

Substance	Mol Wt. (g/mol)	Density (g/ml)	bp, ^oC	Solubility	Hazards
1-butanol	74.12	.81	117-118	Sol water, Miscible alc, ether, and more	Flammable, irritant
H₂SO₄ (con)	98.07	1.84	280	X	corrosive material
sodium bromide	102.89	X	X	X	X
1-bromobutane	137.03	1.27	101.6	Insol in water; sol in alcohol, ether	Flammable, irritant

Quantities used in the reaction and yield data:

Substance	g or mL	Calculated moles	Theoretical Yield moles grams		Actual Yield, grams
1-butanol	mLs		x	x	x
H₂SO₄ (con)	11.5 mL		x	x	x
sodium bromide	13.3 g		x	x	x
Water	15.0 mL	x	x	x	x
1-bromobutane	x	x			Want 7.5 g

A. Assume the above synthesis of 1-bromobutane is known to proceed in 75% yield and you would like to prepare 7.5 g of material. Back calculate how many mLs of 1-butanol you will need for the reaction to synthesize the 7.5 g of product, assuming that the 1-butanol is the limiting reagent. Place this number in the table. Also, calculate all the remaining missing data to fill the table.

Experimental Procedure: The NaBr, 1-butanol, and water are combined in a round-bottomed flask containing a stir bar and cooled to 0 ^oC. Concentrated sulfuric acid is slowly added with stirring. The reaction flask is then prepared for a 50-minute âbriskâ reflux using a heating mantle. After reflux, two layers will be present. The condenser is removed and replaced with a distillation apparatus. Distill the mixture, recording the temperature range, until no more water- insoluble droplets are collected and the temperatures reaches around 115 ^oC. (The boiling point is elevated due to azeotropic distillation of the water with the 1-bromobutane and increasing amounts of sulfuric acid).

B. Propose a way that you could test if the droplets coming over are âwater-insolubleâ.

Be specific with the manipulations, glassware, and what observation you would see.

The collected liquid is transferred to a separatory funnel and 10 mL of water is added. Two layers form, the bottom being the 1-bromobutane layer. The layers are separated, one through the bottom and one through the top, and the separatory funnel is cleaned and dried. The bromobutane layer is returned to the separatory funnel and washed with ice-cold sulfuric acid to remove traces of the starting material, butene and ethereal by-products.

C. Will the top or bottom layer be the bromobutane layer when washing with concentrated sulfuric acid? Why?

The sulfuric acid layer is removed and the 1-bromobutane is washed with 10 mL 3 M NaOH followed by 10 mL aqueous sodium chloride (brine).

D. What is the purpose of each of these washes?

NaOH â

Brine -

Care should be taken to save the correct layer. The 1-bromobutane is then dried over anhydrous CaCl₂.

E. How will you decide how much drying agent to use? How will you know that the 1-bromobutane is dry.

The product is distilled to obtain a clear, colorless liquid.

F. TLC â Suppose you wanted to follow the above reaction by TLC.

a. Describe how you would go about finding a good solvent or solvent pair to use.

b. Suggest a specific solvent system you would try.

c. Draw below what you would want the TLC plate to look like and show the expected relative R_f values for the 1-butanol and 1-bromobutane. Label the spots, baseline, and solvent front.

Experiment: Extraction to seperate benzoic acid and naphthalene.

Procedure-

Place 2 g of a 1:1 (by weight) mixture of benzoic acid and naphthalene in a small beaker; record the exact mass of the mixture in your notebook. Add 35 mL of dichloromethane to the beaker and stir until the solid mixture has completely dissolved. Carefully pour the solution into a separatory funnel.

Add 20 mL of 3.0 M NaOH to the separatory funnel, stopper it, and shake the mixture with frequent venting. When the layers have separated, drain the bottom portion into a clean flask. Pour the aqueous layer into another clean flask labeled âaqueous layer.â Pour the organic layer back into the separatory funnel and extract with a second portion of 3.0 M NaOH. Drain the bottom layer into a clean flask labeled âorganic layerâ and pour the aqueous layer into the âaqueous layerâ flask.

Put the organic layer back into the separatory funnel and shake with 20 mL of saturated NaCl solution. Drain the organic layer into a clean, dry flask and add a small amount of anhydrous calcium chloride to dry the solution. Allow this solution to stand for at least ten minutes, with occasional swirling, then remove the drying agent by gravity filtration; place the filtrate in a round-bottom flask and remove the solvent by simple distillation or by using the rotovap. Once the dichloromethane has been removed, scrape the crystals out of the round-bottom flask into a clean, labeled, tared vial, and determine the weight and melting point of the naphthalene crystals.

Acidify the combined aqueous layers with 6.0 M HCl until the solution tests acidic to litmus paper. A white precipitate of benzoic acid should develop as the solution is neutralized. Chill the solution in an ice bath for at least ten minutes to finish precipitating the solids, then collect the benzoic acid by vacuum filtration. Wash the crystals with a small amount of cold water; then scrape the crystals into a clean, labeled, tared vial and allow to dry. Once the crystals are dry, determine their weight and melting point.

Post-Lab Question:

Write a balanced equation (using structures) for the reaction that takes place when the aqueous layer is acidified with HCl. Why does the precipitate form when the solution is neutralized? (HINT: benzoic acid (slightly soluble in water) and sodium benzoate (soluble in water)

CHEM 2152 Lecture Notes - Lecture 6: Diethyl Ether, Sodium Sulfate

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