Recrystillation lab report PDF

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Organic Chemistry Recrystallization lab report...

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Purifying Acetanilide by Recrystallization TECH #703 Kim Nguyen Professor: Dr. Vladimir Zaitsev Teaching Assistant: Estela Ordonez CHEM 3221 – 111030 June 5th, 2020

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Pre-laboratory Answers Question 1: a. Organic solvents should not be heated on Bunsen burner flame because they are potentially flammable. The reason is that organic solvents have very low vaporization points, which means they also have very low combustion temperature. In addition, organic solvents should be heated in water bath or hot plate. b. We should add activated carbon to a cool solution and then heat the mixture to boiling rather than add the carbon to a boiling solution because adding of activated charcoal to boiling solution can cause the solution to boil over and burn skin. Question 2: Procedure to solve the following recrystallization problems a. Oiling out: Use a recrystallizing solvent with a lower boiling point than its melting point to avoid the oiling out. b. Lack of crystal formation: Add a small amount of a pure solid called seed crystals to start the recrystallization process or scratching the side of the glass. c. Presence of colored impurities: Use activated carbon, which is also called “decoloring carbon”. It has a high affinity to absorb the colored impurities. In addition, we filter the mixture using gravity filtration method. d. Premature recrystallization in the funnel stem during gravity filtration: should be solved by pre-heating the funnel shortly before filtration. Question 3: Methanol would be a good recrystallizing solvent for compound A because it is very volatile, which makes it easier to remove from the crystals than water, and it dissolves the solute when the solution is hot, but not when it is cold. Question 4: a. The smallest volume of boiling water could be used to dissolve 500mg of phthalic acid is = 500 mg / (18 / 100mL) = 2.78 mL b. The percent recovery of phthalic acid in this experiment = (380mg / 500mg) x 100% = 76% c. The loss of phthalic acid can be caused by absorption of phthalic acid by calculation of too much activated carbon, not allowing the solution to sufficiently cool, or not allowing sufficient time for the crystals to precipitate.

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Introduction a. Purpose: In this experiment, we will learn how to separate and purify acetanilide from a mixture by recrystallization. b. Background required: measuring mass, volume, and melting points. Table of Physical Constants

Substances Quantity

Molar Melting mass Point (g/mol) (°C)

Boiling Point (°C)

Density (g/ 3 cm ¿

Hazards

1g

135.17

114.3

304

1.22

2 mL

58.08

-95.0

56

0.784

Carbon, activated

60 mg

3550

500600°C

2.10

Ethanol

2 mL

100 to 1000 Daltons 46.07

-114.1

78

0.789

Petroleum ether

2 mL

82.2

< -73.0

35 - 60

0.653

Acetanilid e Acetone

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Dermatitis and eczematous skin eruptions; anemia and cyanosis. Eyes, nose, and throat irritation; dermatitis. Eye, skin, and eye irritation. Inhalation can cause irritation of mucous membranes. Severe eye irritation, moderate skin irritation, gastrointestinal irritation with nausea, vomiting, and diarrhea; headache, dizziness, unconsciousness, and coma. Dizziness and drowsiness if inhaled, and high concentrations may result in central nervous system depression, and loss of consciousness.

Experimental Procedure / Observations / Data 1. Choosing a Recrystallization Solvent Label your four test tubes with names of all the solvents, which are “acetone”, “water”, “ethanol”, and “petroleum ether”. Weight and place about ~100 mg of crude acetanilide into each test tube. Pulverize the acetanilide using a microspatula. Place 2.0 mL of the appropriate solvent into each test tube then stir each mixture thoroughly. Record whether the acetanilide is soluble and insoluble in each solvent at room temperature. o Water: acetanilide is insoluble at room temperature o Acetone: acetanilide is soluble at room temperature o Ethanol: acetanilide is soluble at room temperature o Petroleum ether: acetanilide is insoluble at room temperature Select the test tubes that contain the solvents in which acetanilide did not dissolve at room temperature, which is water and petroleum ether. Heating the mixtures to boiling using a sand bath, then record whether acetanilide is soluble or insoluble in each hot solvent. o Water: acetanilide begins to dissolve while reaching water’s boiling point. o Petroleum ether: at petroleum ether’s boiling point, acetanilide has not dissolved. Let the heated solvents cool slowly. Meanwhile, prepare an ice-water bath by half-filling a 250 mL beaker with equal volumes of ice and water. Place the tube containing water and acetanilide into the bath for 5 minutes and observe whether recrystallization occurs and record the observations. o Water displays crystallization upon cooling. o The recrystallized product is cold, ice-like, and colorless. Droplets appear around the test tube, making it blurry. Choose an appropriate solvent from which to recrystallize acetanilide.

o Water is chosen to be the appropriate solvent to recrystallize acetanilide o The reason is that acetanilide readily dissolves in water at water’s boiling point but not dissolve at room temperature. In addition, water does not react with acetanilide to be purified.

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2. Dissolving the Compound Obtain ~500 mg (= 0.5 g) of acetanilide and place it into a 25 mL Erlenmeyer flask. In a separated 50 mL flask, place 20 mL of the appropriate recrystallizing solvent, which is water. Add acetanilide then heat the solvent to boiling on a hot plate. Pick up the hot flask containing solvent using beaker tongs. Add 0.5-1 mL of boiling solvent to the flask containing the acetanilide using a Pasteur pipet. Stir the mixtures thoroughly until it dissolves. Once the acetanilide dissolves, remove the flasks from the hot plate. Transfer the dissolved acetanilide solution through a funnel. A few mL of water (solvent) were used to aid in the transfer of crystals remaining in the flask. Let the collected acetanilide solution cool down in an ice bath. Observe the solution color, record the observations, measure, and record the solvent volume. o Observation: the product appears to be cold, viscous, and colorless. It is not totally ice-like or crystals-like. An amount of crystals may have been formed but not apparent. 3. Decoloring the Solution Weight out 60 mg of activated carbon then simultaneously conduct procedure in part A and B. a. Heating the Gravity Filtration Apparatus Place 20 mL of the recrystallizing solvent (water) into a 100 mL beaker. Add acetanilide then heat the water to boiling on a hot plate. Preheat the filtration apparatus by pouring the solvent through the funnel containing a fluted filter paper. Do not add acetanilide into the funnel. Collect the water in another beaker. Place the gravity filtration apparatus on the hot plate to keep the water hot. b. Adding the Activated Carbon Meanwhile, add 60mg of activated carbon to the Erlenmeyer flask containing acetanilide solution. Reheat the solution to boiling. when both parts A and B are completed, pour the boiling solvent from the filtration apparatus beaker into the other 100 mL beaker. Filter the boiling solution containing the carbon through the gravity filtration apparatus while it is still hot from recrystallizing solvent. Collect the liquid in the 25 mL receiving flask. Observe the color of the filtered solution and record the observations. o Observations: the color of the solution changes from dark, cloudy black to colorless. 4. Recrystallizing Pure Acetanilide

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Let the decolorized solution containing the acetanilide to cool to room temperature. Once the room temperature is reached. Place the Erlenmeyer flask into an ice bath for 5 minutes to complete the crystallization. 5. Collecting, Washing, and Drying Crystals Prepare a washing solvent by placing 5 mL of the recrystallizing solvent into a test tube. Let the tube cool in an ice-water bath. Weight a filter paper and record its mass, which is 0.18g. Turn on the water to the aspirator and moisten the filter paper with a few drops of recrystallizing solvent once the recrystallization is completed. Swirl the flask containing the acetanilide and pour the crystals and mother liquor into the funnel, using a glass rod to direct the crystals to the middle of the filter paper. Release the vacuum by loosening the screw clamp on the trap after the mother liquor has been pulled into the filter flask. Remove the funnel from the filter flask and pour the mother liquor into a beaker. Tighten the screw clamp and reattach the funnel. Rinse the remaining crystals of acetanilide from the Erlenmeyer flask using 4-5 mL portions of the mother liquor. Wash the crystals in the funnel with cold water. Let the crystals dry by pulling air through the funnel for 10 minutes. Remove the filter paper and crystals. Weigh the dried crystals and filter paper and record the mass. Observe the color and shape of the crystals and record the observations. o Crystals + filter paper mass = 0.207 g o Crystals mass = 0.207 – 0.180 = 0.027 g o Observations: the crystals lay on the filter paper. They appear to be light and white. Measure and record the melting point ranges of both crude and recrystallized acetanilide. o Melting point: 112.7 – 114.3°C o Melting point range: 1.6°C

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Calculations % recovery =

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mass of recrystallized compound , g ⋅100 % mass of crudecompound , g 0.027 g ⋅100 % = 5.40% = 0.500 g

Results and Discussion The percentage of recovery calculated in this experiment is 5.40%, which is relatively low. The maximum percent recovery can be up to 85%. The data indicates that the initial sample had a high concentration of impurities. On the other hand, the melting point of the recrystallized acetanilide is 112.7114.3°C and the melting point rage is 1.6°C. The collected data suggests that the recrystallized product contain pure acetanilide. In addition, we have chosen water to be an ideal recrystallizing solvent for acetanilide because it matches the criteria. Based on this experiment, acetanilide did not

dissolve in water at room temperature but did at water’s boiling point temperature. Moreover, water does not react to acetanilide. Hence, water is an ideal recrystallizing solvent for acetanilide. VII.

Conclusion In today experiment, we have succeeded in learning a simple method for recrystallization technique. We have learned the criteria for selecting a recrystallization solvent and purify acetanilide from a mixture by the learned technique. In addition, we have also learned to decolorize a solution by heating the gravity filtration apparatus and adding activated carbon. In the first part of this experiment, we have chosen water to be an idea recrystallizing solvent for acetanilide. The reason is that acetanilide does not dissolve in water at room temperature but dos at water’s boiling point temperature. By the end of this experiment, we have managed to calculate the percentage of recovery and the melting point of the recrystallized product. The percentage of recovery is 5.40%, which is relatively low and indicates that the initial mixture contains a high concentration of impurities. In addition, the melting point of the recrystallized acetanilide is 112.7-114.3°C, which suggests that the recrystallized acetanilide is pure.

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Post-Laboratory Answer Question 1: a. The minimum volume of water needed to dissolve 1.00g of benzoic acid at 100°C is v = 100 / 6.84 = 14.62 mL b. The amount of undissolved benzoic acid = 1 – 0.051 = 0.949g The maximum theoretical percent recovery from the recrystallization of 1.00 g of benzoic acid from 15mL of water, assuming the solution is filtered at 25°C, is = (0.949 / 1.000) x 100% = 94.9% Question 2: a. The amount of recovered acetanilide = 500mg – (5mg / 1mL) x 15 mL = 425 mg. This is also the maximum mass of the substance recovered. The maximum percent recovery = (425mg / 500mg) x 100% = 85% b. The percent recovery of the acetanilide produced in this experiment is 5.4% c. The percent recovery of acetanilide produced in this experiment is very low compare to the maximum percent recovery. The reason might be the cooling temperature used in this experiment is relatively lower than its in this problem. Question 3: a. Adding 5 mL instead of 0.5 mL portions of boiling solvent, which is 10 times more than required, would make the percent recovery of acetanilide be less.

b. Not pre-heat the gravity filtration apparatus would lower the temperature of the solution and lead to prone to premature recrystallization while filtering the solution. c. Not cooling the solvent and washing the crystals with room temperature solvent may dissolve an extra amount of crystal and take away with it, which is results will affect the percent yield of recrystallization. Hence, it can decrease the percent recovery....