Exp #3 report - Recrystallization and melting point PDF

Preview

Summary

Recrystallization and melting point...

Description

Experiment #3 Report Connor Morris Chem 253 – 014: Peter Rietgraph Lab: Recrystallization and Melting Point 09/13/2016 Purpose The purpose of this experiment was to purify a crystalline organic compound and discover the melting point of that compound. The procedure used to purify the compound Naphthalene was called recrystallization. Theory There are many ways to purify a liquid or a solid. Because we are using a solid compound, we used a process called recrystallization to purify the substance. This process requires the compound to be dissolved in a warm solution of a specific solvent, and then cooled in order to form a recrystallized solid. In this experiment, Naphthalene was the substance being purified. It was first dissolved in methanol, and then cooled to allow crystals to form. The slower the crystals formed the purer the substance becomes. Any impurities could potentially skew the results as well as the melting point of the substance. Once the pure substance has been isolated, we could test the melting point of the compound. The closer the melting point is to the theoretical melting point, the purer the substance being tested. Reaction Cinna

mic Acid

Naphthalene

Urea

Benzoic Acid

Yield Calculations: Amount started with = 0.500g Amount formed after recrystallization = 0.400g Percent yield = 0.400/0.500 = 80% Methods/Procedures The experiment was followed verbatim from the lab manual found on pages 21-22. Benzoic acid, urea, naphthalene, and cinnamic acid are all irritants to the skin, eyes, and

respiratory systems and should be handled with care. Naphthalene is flammable so it cannot be dried in the oven or else it will catch on fire. Gloves and eye protection were required in this lab. Observations/Results There are a few problems that could have altered the yield of our product. When we were cooling our substance to allow crystals to form, we might not have waited long enough, and some impurities could have remained which could change the melting point of the substance. Also, when transferring the solid crystal compound to the Buchner funnel, there was some remaining substance that couldn’t be retrieved from the test tube. This could affect the ending weight of the dried substance. Another factor that could have affected the ending weight of the purified substance was not waiting long enough for the naphthalene to dry before taking its weight. The melting point temperatures recorded were very similar to the temperatures from the lab manual. The ending purified substance was a milky white solid that didn’t have an odor. Discussion/Conclusion Everything in the experiment besides the minor human error occurrences explained in observations/results went as planned. It was concluded that a crystalline organic substance such as naphthalene could successfully be purified by the recrystallization process, and measured by using the melting point to determine the level of purification of the substance. Exercises 2) Minimum volume of water required: 200g x 1.4 ml/ 1g = .28ml. Sodium benzoate remaining: .28ml x 1g/1.8ml = .156g Max mass of solid that can be recovered: .200g - .156g = .044g 4) Compound Y is oxalic acid because this substance has the lowest melting point, and when it is mixed with the other substances, their melting points are lowered as well. 6) A. If there was twice the amount of water, the impurities wouldn’t be able to be dissolved all the way, which would affect the total yield. The melting point would also likely increase due to unwanted impurities. B. If the naphthalene wasn’t completely dried, the total yield would be altered because the substance wouldn’t have completely finished its purification process. This would also raise the substances melting point. C. If the benzoic acid solution was placed directly into the ice bath without being allowed to cool first, the solvent wouldn’t be able to dissolve completely. Because of this, there would still be impurities in the solution which would then crystallize and affect the total yield. These extra impurities would increase the melting point of the substance....