Experiment 3- Recrystallization and Melting Point PDF

Preview

Summary

Exp. 3...

Description

Lab 3: Recrystallization and Melting Point February 11th, 2021 Purpose: The purpose of this experiment was to purify a crystalline organic compound and discover the melting point for the compound. To be able to determine the percent of naphthalene from recrystallization and to determine the melting points of urea, cinnamic acid and the unknown mixture of the two. Theory: Recrystallization is a technique that is used to purify. Often times it is used when a substance is dissolved in a solvent and then it is cooled to form crystals of the pure substance. Some of the substance may still remain within the solution due to that it is important to remember to use as little solvent as possible. Melting Point can be used to determine the identity of the substance as well as the purity of the substance by comparing the melting range of the unknown substance to the melting point ranges of known substances. When the melting point is closer to its theoretical melting point, the purer the substance is. Reactions:

Urea

Cinnamic Acid

Naphthalene

Methods and Procedures: The experiment was followed verbatim from the lab manual on page 20-21; with the following exceptions: In step 2, two boiling chips were used while boiling and then removed before the solution was allowed to crystalize. The following chemicals were used during the experiment; naphthalene, cinnamic acid and urea. These chemicals are all irritants to the eyes, skin and lungs. Goggles and eyewear were worn at all times during the experiment. During the lab, experimenters avoided breathing in the chemical fumes. Naphthalene is also flammable; it was kept away from heat and the crystals were dried at room temperature instead of using an oven in order to avoid combustion. Observations and Results: The naphthalene dissolved after adding about 6 mL of ethanol which was more than the calculated value of 5 mL. There are a few problems that could have altered the outcome of this experiment. Also, when transferring the solution to the Buchner funnel, there was some substance still left in the test tube that was unable to be recovered. This could have affected the

end weight of the crystals. The crystals could have longer time to dry to the remove the excess liquid, but it was important to avoid using the oven due to the flammability of naphthalene. The yield from the recrystallization of naphthalene was 0.497 grams; less than the initial 0.50 grams, as expected. The melting point ranges were found as followed.  Naphthalene: 72 – 75  Cinnamic Acid: 130 - 132  Urea: 125 - 130  Cinnamic Acid/ Urea Mixture: 100 – 107 Since the oven was not used to dry the naphthalene solution, it is possible that the actual percent recovered should be less than found. This could have also caused the melting point to change for the naphthalene, as the crystals didn’t get too dry for long enough. Discussion and Conclusion: The experiment besides the minor human errors explained in observations and results went as planned. In conclusion, the crystalline organic substance naphthalene was successfully purified by recrystallization and was measured by using melting point to determine the level of purification of the substance. Exercises:...