Lab Report Recrystallization September 27, 2016, Exams of Chemistry

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Chem2211L

Lab Report

Recrystallization

September 27, 2016

Experiment #3: Recrystallization Experiment Date : September 20, 2016 Lab Partners : Judienne Archer Tonja Bryant Alexis Dunn Objective : To separate benzoic and acetanilide impurities by the technique recrystallization and to calculate the percent recovery of benzoic acid and acetanilide after recrystallization. Theory : As the temperature increases, the amount of solute dissolved in the solvent increases also. Introduction: Pure homogeneous compounds consist of the same molecules and have similar structures. These compounds may not be totally pure due to possible amounts of contaminants. The process of recrystallization can be used to purify a solid and remove the impurities. Recrystallization heats or cools a solvent then filters the impurities. Any impurity present in a solid sample will remain in the aqueous solution and only pure solute will be on the filtered paper.

crude acetanilide, 2 spatulas of activated charcoal, 3 boiling chips, and 30 mL of distilled water was weighed and added to the flask. The above process is repeated with acetanilide. Results & Calculations: MW of benzoic acid (C 7 H 6 O 2 ) = 122.12g, MW of acetanilide (C 8 H 9 NO) = 135.16g, MW of deionized water (H 2 O) = 18.02g. Weight of crude benzoic acid: 2.0g Weight of filter paper: 0.18g Actual weight of benzoic acid: 1.82g Weight of crude acetanilide 2.0g Weight of filter paper 0.18g Actual weight of acetanilide 1.82g After recrystallization: Weight of benzoic acid 1.70g Weight of filter paper 0.18g Weight of acetanilide: 1.78g Weight of filter paper 0.18g Limiting Reactant: Benzoic acid 2.0 g C 7 H 6 O 2 x 1 mol C 7 H 6 O 2 x 18.02g H 2 O = 0. 295 mol C 7 H 6 O 2 122.12 g C 7 H 6 O 2 1 mol H 2 O Acetanilide 2.0 g C 8 H 9 NO x 1 mol C 8 H 9 NO = x 18.02g H 2 O = 0. 266 mol C 8 H 9 NO 135.16 g C 8 H 9 NO 1 mol H 2 O

Theoretical Yield (T.Y.): Benzoic acid 1.52 g x 1 mol C 7 H 6 O 2 x 18.02g H 2 O = 0.224g C 7 H 6 O 2 122.12 g C 7 H 6 O 2 1 mol H 2 O Acetanilide 1.60 g x 1 mol C 8 H 9 NO x 18.02g H 2 O = 0.236g C 8 H 9 NO 122.12 g C 8 H 9 NO 1 mol H 2 O % Yield: Benzoic acid 0.224g x 100% = 75.9% 0.295g Acetanilide 0.236g x 100% = 88.7% 0.266g Percent recovery: Benzoic acid 1.52 (1.70 – 0.18(filter paper) x 100 = 83.5% 1.82 (2.0 – 0.18 (filter paper) Acetanilide 1.60 (1.78 – 0.18(filter paper) x 100 = 87.9% 1.82 (2.0 – 0.18 (filter paper) Discussion and Conclusion: The technique recrystallization was used because it is a simple method to purify a solid compound. The percentage yield for benzoic acid and acetanilide acid being high indicated the initial sample had a low concentration of impurities. With the melting point being in a specific range it is concluded that benzoic acid and acetanilide is a pure substance after recrystallization was done.