CHE_LAB3(RC)

CHE_LAB3(RC) - Compound Purification by Recrystallization...

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Compound Purification by Recrystallization Experiment #3
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Purpose Recrystallization is a widely used technique that is essential for the purification of many compounds. Recrystallization is a result of dissolving impure or crude crystals and cooling them in solution to saturate the solution in order to recrystallize the compound in its pure form. The lab focuses on recrystallization techniques and testing the success of it. Results and Discussion Purification of a Solid by Recrystallization 1,4-dimethoxybenzene was purified by first creating a solution with 1g of 1,4- dimethoxybenzene and 3 ml of ethanol in a 10ml Erlenmeyer flask. Ethanol was chosen as a solvent due to its polar properties. Since both the compound and its impurity are polar, ethanol would be able to dissolve both. The compound to be purified is less polar than its impurity and thus it will solidify at a higher temperature. For 1,4- dimethoxybenzene, The 1,4 position of the substituents creates a balancing and canceling effect on the polarity. Thus, the compound has lower polarity than 2-napthol that exhibits a polar hydroxyl group. The respective structures are shown below. The solution was heated to melt the solute and then cooled slowly at room temperature for crystal formation. Since no crystals were seen to form, the glass was scratched slightly to set free a series of rapid crystallization in the flask. The crystals were then dried and extracted. The recorded mass was 0.422 g. Since the initial mass was 1 g we concluded that 42.2% of the compound was recovered. O O CH 3 C H 3 1,4-dimethoxybenzene OH naphthalen-2-ol
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The purity of the recovered compound was then tested by two alternative methods: melting point comparison and thin layer chromatography (TLC). A miniscule amount of crude and purified compound were placed into capillary tubes and then placed into the Mel-Temp apparatus. The recorded melting point range of the crude compound was 43 to 55 ºC. The melting point range for the pure recovered product was 54 to 56 ºC. The
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CHE_LAB3(RC) - Compound Purification by Recrystallization...

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