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Recrystallization Pre-Lab, Lab Reports of Organic Chemistry

University of Georgia (UGA)Organic Chemistry

It is my pre-lab for the recrystallization lab in Organic Chemistry 1 at UGA

Typology: Lab Reports

2022/2023

Uploaded on 09/08/2023

georgia-stinchcomb
georgia-stinchcomb 🇺🇸

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Pre-Lab: Recrystallization
Georgia Stinchcomb – Grs05896
I. Title:
Identifying an Unknown Organic Solid Using Recrystallization
II. Introduction:
Recrystallization is a technique for purifying organic solid compounds. The
purpose of this experiment is to use recrystallization to purify an impure, unknown
substance so it can be identified using its melting point. A small amount of solvent
will be added to the unknown substance. Gravity filtration will be used to separate
any insoluble solids out of the dissolved heterogeneous mixture. For this practice, the
solution will be poured into a funnel with filter paper allowing gravity to pull the
liquid away from the insoluble solids. Suction filtration will be used to remove any
excess crystalized substances in the dissolved mixture. The solution will then be
recrystallized. In this process, the solution is placed in a beaker of ice water to allow
the solution to cool down completely allowing the dissolved solute to recrystallize.
The recrystallized solid will then go through suction filtration. During this process, I
vacuum is attached to a Buchner funnel containing a piece of filter paper and suctions
most of the liquid out of the recrystallized solute. This will allow for more precise
filtration of the liquid from the solute. The left-over crystals will then be heated on a
hot plate in a flask to determine their melting point which can be used to identify the
substance.
III. Table of Reagents:
Reagent
Name
Structure
MW
(g/mole)
Melting
Point (OC)
Acetanilide
135.16
113-115 OC
Benzamide
121.14
125-128 OC
Benzoic Acid
122.12
121-125 OC
pf3
pf4
pf5

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Pre-Lab: Recrystallization Georgia Stinchcomb – Grs I. Title: Identifying an Unknown Organic Solid Using Recrystallization II. Introduction: Recrystallization is a technique for purifying organic solid compounds. The purpose of this experiment is to use recrystallization to purify an impure, unknown substance so it can be identified using its melting point. A small amount of solvent will be added to the unknown substance. Gravity filtration will be used to separate any insoluble solids out of the dissolved heterogeneous mixture. For this practice, the solution will be poured into a funnel with filter paper allowing gravity to pull the liquid away from the insoluble solids. Suction filtration will be used to remove any excess crystalized substances in the dissolved mixture. The solution will then be recrystallized. In this process, the solution is placed in a beaker of ice water to allow the solution to cool down completely allowing the dissolved solute to recrystallize. The recrystallized solid will then go through suction filtration. During this process, I vacuum is attached to a Buchner funnel containing a piece of filter paper and suctions most of the liquid out of the recrystallized solute. This will allow for more precise filtration of the liquid from the solute. The left-over crystals will then be heated on a hot plate in a flask to determine their melting point which can be used to identify the substance. III. Table of Reagents: Reagent Name Structure MW (g/mole) Melting Point (OC) Acetanilide 135.16 113 - 115 OC Benzamide 121.14 125 - 128 OC Benzoic Acid 122.12 121 - 125 OC

Ethyl 3,5- dinitrobenzoate

240.17 94 - 95 OC

m- Nitrobenzoic Acid

167.12 139 - 141 OC

o-Toluic Acid 136.15 102 - 104 OC Salicylic Acid 138.12 158 - 161 OC Vanillin 152.15 81 - 83 OC IV. Safety Information:

  • Acetanilide: Harmful if swallowed, may cause eye and skin irritation
  • Benzamide: Can cause skin and eye irritation, may cause respiratory or intestinal infections, nausea, vomiting, and diarrhea
  • Benzoic Acid: Can cause skin irritation, eye damage, and damage to organs after prolonged exposure
  • Ethyl 3,5-dinitrobenzoate: highly flammable, can cause skin and eye irritation after handling
  • m-Nitrobenzoic acid: Can cause skin, eye, respiratory, and digestive irritation after exposure
  • o-Toluic Acid: Can cause skin, eye, and respiratory irritation
  • Salicylic Acid: Can cause eye irritation, harmful if swallowed
  • Vanillin: can form combustible dust, may cause eye irritation V. Procedure:
  1. Obtain 1g of unknown solid and record the code in lab manual a. Be sure to stir mixture
  2. Add approximately 25-50 mL of water and several boiling chips to a 125 mL Erlenmeyer flask
  3. Heat the water to a gentle boil using a hotplate
  4. Add 1g of unknown solid and a boiling chip to a second 125 mL Erlenmeyer flask and begin heating on second hotplate
  • While dissolving, the crystals clumped slightly
  • Pure substance is a shiny/reflective and white crystal Weight of recovered pure product: 0 .094 g Fast melting point determination: 122 .2 °C – 123 .4 °C Slow melting point determination: 122.0 °C – 123. 2 °C Potential unknown reagent 1: Benzoic acid
  • Mixed MP: 121 °C – 124 °C Potential unknown reagent 2: Benzamide
  • Mixed MP: 125 °C – 129 °C VII. Results: For this experiment the unknown impure sample’s code was RC944945. The initial weight of the impure mixture was 1.003 grams. Approximately 25 mL of water was used to dissolve the impure mixture. After being placed in an ice bath, crystals began forming. After suction filtration the new pure substance weight 0 .094 grams. The fast-melting point of the pure substance was found to be 122.2 °C – 123. 4 °C. The slow melting point of the new pure substance was found to be 122.0 °C – 123. 2 °C. This led to the selection of two potential identities for the pure substance. Benzoic Acid was the initial selection with a mixed melting point 121 °C – 124 °C. The second selected identity was Benzamide with a mixed melting point of 125 °C – 129 °C. VIII. Discussion: From the data collected it was found that the unknown pure substance was Benzoic Acid. Benzoic Acid has a melting point of 121 °C – 125 °C. Out of the possible reagents from the reagents table, Benzoic Acid is the reagent with the closest melting point to the pure substance. In the mixed melting point test, this was proved further. The mixed melting point was 121 °C – 124 °C which is almost the same as the melting point of the pure substance 122 °C – 123 °C. The second closest reagent tested was Benzamide. During this mixed melting point test the melting point was significantly raised to 125 °C – 129 °C. While the data gathered supports the theory that the unknown substance was benzamide, there are a few issues that may have occurred when determining the melting point of the purified substance. The biggest issue that may have occurred was during the dissolving process. When attempting to dissolve the pure substance, the substance began recrystallizing before it was placed in the suction filtration set up. Because of this, the dissolved solution had to be poured through the suction filtration system faster than planned and this way have caused impurities to get past the filter paper. This could have caused the melting point data to be skewed slightly. IX. Post Lab Questions:
  1. Consider a heterogeneous mixture of two unknown solids (Q & S). Determine which of the following solvents (dimethylsulfoxide, ethyl acetate, or dichloromethane) would an appropriate choice (or choices) for isolating and recrystallizing Unknown Q from Unknown S? Explain the reasoning behind your decision(s) in detail. In addition, explain why the remaining solvent (or solvents) would not be acceptable options for the proposed experiment.

o The best option for the dissolution of S and Q would be Dimethyl Sulfoxide. This can be determined using the given solubility levels for S and Q. The solubility for Q in this substance is extremely low (0.005 and 0.047). However, the solubility levels of S are higher at both temperatures (0.157 and 7.14). In dimethyl sulfide, the solubility levels of S and Q have the largest difference meaning it is more likely that S will dissolve while Q stays solid. This would allow Q to be filtered out much easier to isolate S. The remaining solvents have much more balanced solubility levels that would cause Q to have a less likely possibility of remaining solid. The solubility levels for S are also much lower, so S would have a less likely chance of dissolving as well.

  1. If you allowed your solution of hot water, impurities, and solute to cool on the benchtop before employing a room temperature gravity filtration, what is the most likely outcome for your separation? Will it result in a successful separation of the solute and impurities? What is likely to happen with your solution under these conditions? Explain your reasoning in detail. o If allowed to cool back to room temperature, the pure substance is likely to reprecipitate into its solid form. This would lead to an unsuccessful filtration because the pure substance precipitate would be filtered out of the solution.
  2. After recrystallizing and isolating an unknown, crystalline solid, you obtain a preliminary melting point range of 132- 137 oC. Identify your purified unknown using the table below. Which of these compounds is your unknown most likely to be? How did you arrive at your decision? Explain your reasoning in detail. o A compound with the melting point range of 132 °C – 137 °C would likely be Cinnamic Acid (133 °C – 135 °C). While the melting points are not exact, the melting point of the unknown substance most closely resembles that of Cinnamic Acid.
  3. A crystalline compound, K, is known to be soluble in dimethylformamide (DMF) at 41 oC. It is possible to dissolve a total of 20.12 g of solid K in 150 mL of DMF. If you are given a 25.4 g sample of this unknown compound, assuming that any impurities present are insoluble in dimethylformamide at room temperature, what is the precise volume of DMF you would require to perform a full recrystallization of solid K? In order to receive full credit, you must show your calculations and explain your reasoning. o If 150 mL of DMF are necessary to dissolve 20.12 grams of K, then in order to dissolve compound K, 189 mL of Dimethylformamide will be needed. 25. 4 𝑔
  4. 12 𝑔
  1. After recording a preliminary melting point range of 140- 147 oC for an unknown solid, you identify it as o-nitrobenzoic acid. Running a mixed melting point determination with o-nitrobenzoic acid affords a melting point range of 126-