Recrystallization of Benzil Lab Report, Lab Reports of Organic Chemistry

Download Recrystallization of Benzil Lab Report and more Lab Reports Organic Chemistry in PDF only on Docsity! Title: Recrystallization of Benzil by Tarika Arjune Experiment performed: September 30th,2021 Report Due: October 28th,2021 Abstract: We performed the recrystallization of benzil to purify a solid organic compound. We added methanol to the benzil and heated it till it boiled. The solution was removed from heat and cooled in an ice bath then 15mL methanol was added. The solution was heated to boiling point and removed then cooled once again. Charcoal was added to the solution to remove colored impurities then boiled once again. The solution was filtered and washed with 30 % methanol then the solution was heated to boiling as water was added. We removed the solution from heat and added it to an ice bath then we used vacuum filtration to separate the crystals. Once the crystals are dried, we calculated a 50% yield from recording 0.5 grams of product we collected. Objective: The purpose of this lab is to purify a solid organic compound, recrystallizing benzil. Introduction: Recrystallization is a seven-step method used to purify solid organic compounds. Recrystallization considers four important concepts such as solubility, saturation level, exclusion, and nucleation. Recrystallization involves dissolving the material to be purified or the solute in a hot solvent to yield a solution and solubility. When the solvent cools, the solution is saturated and then recrystallizes. The crystal formed is a single pure substance in which impurities are excluded. Impurities in the structure do not allow for the crystalline structure to form. A pure crystalline organic substance is held together by London Forces which is weak and will melt from 22 C to 250 C. Soluble impurities remain in the solution if they are not concentrated enough to saturate it and therefore crystallize. Recrystallization of a solute occurs at nucleation. There are seven steps to recrystallizations which include choosing the solvent, dissolving the solvent, decolorizing the solution, filtering impurities/ suspended solids, recrystallizing the solute, collecting/ washing crystals, and drying the product. In the recrystallization of benzil, we add methanol and continuously heat and cool the substance. We add charcoal to remove the impurities and then we filter the solution through the filter paper and dry and separate the crystals through vacuum filtration. Reactions/Schemes/Mechanisms: boiling and cooling of the substance change in color from yellow to green accumulation of bubbles when methanol added Materials: ● Benzil: added to the Erlenmeyer flask to recrystallize ● Methanol solution: added drops to benzil till it was dissolved ● Boiling Chips: allows the liquid being boiled to not become overheated ● Hot plate: used to heat the methanol and benzil mixture till boiling ● Charcoal pellets: added to remove colored impurities from the solution ● Metal spatula: used to scoop the charcoal powder ● Filter paper: used to separate the solids from the liquid in the solution Table of Physical Constants: Name Structure MW (g/mol) MF bp/mp (C) Density (g/cm3) Solubility (g/L) Benzil 210.23 g/mol C14H10O2 bp: 346-348 C mp: 94.8C 1.23 g/cm3 Soluble in Benzene Insoluble in water Methanol 32.04 g/mol CH3OH bp: 64.7oC mp: -97.6oC 0.792 g/cm3 miscible Wikipedia Foundation. (2021). Benzil. Wikipedia Foundation. (2021). Methanol. Procedure: Procedure Observations 1. Choose an appropriate solvent, a good solvent is one when you place a few crystals of solute in it at 22 they do ℃ not dissolve instantly. 2. Add 1g of benzil and 1.5ml of methanol into a 50ml Erlenmeyer flask with a boiling chip, then place the flask onto a hot plate and heat until it boils. 3. Using a dropper, start to drop methanol until benzil dissolves. Very bright yellow, clumpy substance Accumulation of bubbles 4. Remove the flask from the heat and cool it in an ice bath and add the remaining 15ml of methanol. 5. Heat the solution to boiling point 6. Remove the flask from the heat and let it cool. 7. Add 1 spatula of decolorizing charcoal pellets in order to remove any colored impurities from the solution and then heat the solution to the boiling point for 2 mins. if color is still present, add more of the pellets and boil Substance turns green in color with the addition of black spots *Added too much charcoal 8. Filter the solution in a warm stemless funnel with filter paper into another 50ml Erlenmeyer flask. 9. Wash the used Erlenmeyer flask and the filter paper with 2ml of hot 30% methanol by using a Pasteur pipette and dropping the solvent around the upper rim of the filter paper. 10. Heat the solution to the boiling point and add water drop by drop from a 10ml graduated cylinder using the pipette. 11. Swirl the flask around and heat up to dissolve any of the benzil precipitates 12. Remove the flask from heat and allow it to cool in an ice bath. 13. Use a 50mm Bunchner funnel to separate the crystals from the cold mixture by using Vacuum filtration. 0.2g= weight of filter paper 14. Dislodge the crystals when collecting the product by using a spatula to scrape them out of the flask. any crystals remaining in the flask can be washed out with the 30% methanol Filter paper=0.2g After drying=0.7g 0.7g-0.2g=0.5g 15. Dry the crystals and take the percent yield. there should be less than 1g of crystalline benzil % yield = recovered mass/original mass(1g) *100 0.5g/1g *100 = 50% 50% yield Substance end color was green and flaky in appearance Flow Chart: Add 1g benzil and 1.5mL of methanol to Erlenmeyer flask with boiling chip and boil till dissolves