Organic Chemistry Lab 1 PDF

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Organic Chemistry Lab 1...

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Laboratory Exercise 1 Purification of a Solid: Crystallization and Melting Point Section A56 Conducted on 9/13/16

Introduction:

The objective of this lab was to identify an unknown solid by recrystallizing it and then by determining its melting point. In order to do this, basic experimental techniques, as well as basic glassware and apparati that are commonly used in the organic laboratory were introduced. These basic organic laboratory techniques consisted of thermometer correction, recrystallization of a solid, melting point determination, and two types of filtration: gravity and vacuum. Procedure: 1. Determination of Melting Point and Thermometer Correction a. Pure benzoic acid was obtained and placed in a capillary tube. b. Using a Digi Melt, the melting point was determined. c. By comparing the observed melting point with the known melting point, the thermometer correction was calculated. 2. Recrystallization and Identification of an Unknown Organic Solid Acid a. An unknown impure solid acid sample was obtained from the TA. b. 3.00g of the sample was measured out and transferred into a 250ml Erlenmeyer flask. c. 50ml of distilled water was added to the flask and the flask was placed on a hot plate. d. Once all of the sample was dissolved, the flask was removed from the hot plate and decolorizing charcoal was added. e. After the solution boiled on the hot plate for a few minutes, it was removed from the heat and the color of the solution was examined. More charcoal was added if there was no noticeable change in color and the solution was re-heated. f. The hot solution was filtered into a different Erlenmeyer flask using fluted filter paper. g. After the solution was cooled, the product was collected using vacuum filtration. In order to assist with crystal formation, the inside of the flask was scraped multiple times with a glass stirring rod. h. The product was dried and it’s melting point was determined using the Digi Melt. Its weight was also measured, and percent recovery was calculated. i. Using the table provided in the lab manual, the unknown sample was identified.

Reagents Table Name

Molecular Formula

Molecular Mass

Benzoic Acid

C7H6O2

122.1213g

Melting Point 122.4℃

Adipic Acid

C6H10O4

146.1412g

151.5℃

Diagram

Phthalic Acid

C8H6O4

166.1308

230℃

Salicylic Acid

C7H6O3

138.1307g

158.6℃

pAminobenzoi c Acid

C7H7NO2

137.1360g

188.5℃

2Chlorobenzoi c Acid

C7H5ClO2

156.5664g

142℃

Data Tables Part One: Determination of Melting Point- Thermometer Correction Melting Point Apparatus Number 24 Standard Melting Point of Benzoic Acid 122.4℃ Digi Melt Temperature 1 (Benzoic Acid) 121.6℃ Digi Melt Temperature 2 (Benzoic Acid) 124.4℃ Average of Digi Melt Temperatures 123.0℃ Thermometer Correction 122.4℃ – 123.0℃ = -.6

Part Two: Recrystallization and Identification of an Unknown Organic Solid Acid Unknown Sample Number 27

Mass of Unknown Sample Before Recrystallization Weight of Filter Paper (first round of crystal collection) Weight of Filter Paper (second round of crystal collection) Weight of Unknown Sample After Recrystallization Including Filter Paper (first round of crystal collection) Weight of Unknown Sample After Recrystallization Including Filter Paper (second round of crystal collection) Total Weight of Unknown Sample After Recrystallization (Minus filter paper) Percent Recovery Digi Melt Temperature 1 (Unknown Sample) Digi Melt Temperature 2 (Unknown Sample) Average of Digi Melt Temperatures Melting Point of Unknown with Thermometer Correction

3.00g .12g .12g .76g 1.51g 2.03g 67.67% 150.0℃ 151.9℃ 150.95℃ 150.35℃

Unknown Organic Solid Acid: Adipic Acid Observations   

When the unknown sample was dissolved in water, the liquid became yellow. After the solution was heated and charcoal was added, the liquid slowly turned light green. During the melting point determinations, the sample was observed as it turned from a solid to a liquid.

Calculations Thermometer Correction 122.4℃ – 123.0℃ = -.6 Percent Recovery % Recovery = (New Mass/Original Mass) x 100 % Recovery = (2.03/3.00) x 100 = 67.67% Discussion The main point of this lab was to determine the identity of an unknown sample by recrystallizing it and then determining its melting point. 3.00g of the unknown were weighed out, and was then dissolved into 50ml of water in an Erlenmeyer flask. After the sample was fully dissolved, charcoal was added to the flask, and the solution was re-heated. Charcoal was used because it is porous and thus able to filter out any polar impurities contained in the organic solid. Further, charcoal is insoluble and thus can easily be filtered out. Once the solution was cool and the charcoal was filtered out using gravity filtration, a glass stir rod was scraped against the side of the Erlenmeyer flask to assist in the formation of crystals. The small amount of glass that chipped from the side of the flask acted as a base from which the crystals could grow, thus initiating recrystallization. Then, the first round of vacuum filtration was performed. The sink puts pressure on the collection flask, causing it to act as a

vacuum, and pull down anything that fits through the filter paper. The crystals were collected and measured to weigh .64g. Because this weight was so small, the solution was reheated as to boil out any extra liquid that had been added to dissolve the solute. Then, the solution was cooled and unlike the first round of recrystallization, it was placed on ice. Placing the solution on ice, along with the scraping of the side of the flask with the stir bar allowed for more crystals to form, and the second round of recrystallization yielded 1.51g of crystals. Thus a total of 2.03g of crystals were formed in the recrystallization process. The percent recovery was calculated to be 67.67%. While this is a high percent recovery, errors occurred that prevented it from being 100%. One error that may have occurred is that too much solvent was used when dissolving the solute, thus affecting the amount of crystals that were able to form during the recrystallization process. Once the recrystallization was completed, the melting point of the unknown was determined using the Digi Melt. Because the Digi Melt needed to be calibrated, first the melting point of Benzoic Acid was determined, in order to calculate the thermometer correction. It was found that the Digi Melt was .6 degrees low, meaning .6 would need to be subtracted from whatever temperature was found to be the melting point. The melting point of the unknown was found to be 150.35℃.This is comparable to the melting point of adipic acid which is 151.5℃, and thus it was determined that the unknown sample (#27) was adipic acid. This experiment is important because it allowed for important organic chemistry laboratory techniques to be learned, such as recrystallization, melting point determination, and filtration techniques. Further, it emphasizes that compounds have distinct melting points and that these melting points can be used to determine what substance something is. Conclusion This lab was performed in order to gain a better understanding of organic laboratory techniques. By using recrystallization and melting point determination, the identity of an organic solid acid was determined. The recrystallization yielded a percent recovery of 67.67% and the melting point was found to be 150.35℃. This is comparable to the melting point of adipic acid; thus the unknown organic solid acid was adipic acid. Acknowledgements Melia Wakerman, lab partner Julien Viel, TA References 1. Binghamton University Department of Chemistry, Chemistry 335 Laboratory Manual, Fall 2015 Edition 2. http://chemistry.about.com/od/chemistryfaqs/f/charcoal.htm (“What is Activated Charcoal and How Does it Work?”) 3. Handbook of Chemistry and Physics...