The main purpose of this experiment is to purify an impure solid by the technique of recrystallization. This technique involves several steps, selecting an ideal solvent, dissolving the compound in a minimum amount of boiling hot solvent, filtering insoluble impurities while the solution is hot; crystallizing the purified compound, and isolate the pure compound by vacuum filtration . The unknown used in the experiment was #4, which were white crystals. In order to determine the ideal solvent we prepared two test tubes. Test tube #1 containing 0.106g of unknown and 3mL of water, it was well mixed. At room temperature water dissolved a small amount of the solute while boiling hot it was able to dissolve the solid but some impurities remained
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The unknown #4 weighted 0.286g after recrystallized. The percentage recovery was 0.256g/0.500 x 100%=57.2%, meaning that 42.8% (0.214g) was lost during the process. Observing and comparing the results we did not recovered 100 % of the purified compound, therefore there are many factors that affected the crystallization . One of the factors affecting our product was adding too much solvent at at time. Since too much solvent was added, p-hydroxybenzoic pure acid stayed dissolved in the solution, eventually the percentage recovered was lower than it should be. A high percentage yield is considered between 70-80% of the purified product, in order to obtain this results we need to use little solvent as possible. On the other hand another factor that affected the results obtained was that we used a folded paper instead of fluted filter paper. A fluted filter paper is preferred over a folded filter paper because it has more surface area and also helps the filtration to take place faster. Since we did not use the fluted filter paper during the filtration some solvent evaporated resulting in premature crystallization and the solute stayed on the filter paper along with the impurities, making the percent recovered lower. The melting point obtained was 216.8-218.1
The unknown #4 weighted 0.286g after recrystallized. The percentage recovery was 0.256g/0.500 x 100%=57.2%, meaning that 42.8% (0.214g) was lost during the process. Observing and comparing the results we did not recovered 100 % of the purified compound, therefore there are many factors that affected the crystallization . One of the factors affecting our product was adding too much solvent at at time. Since too much solvent was added, p-hydroxybenzoic pure acid stayed dissolved in the solution, eventually the percentage recovered was lower than it should be. A high percentage yield is considered between 70-80% of the purified product, in order to obtain this results we need to use little solvent as possible. On the other hand another factor that affected the results obtained was that we used a folded paper instead of fluted filter paper. A fluted filter paper is preferred over a folded filter paper because it has more surface area and also helps the filtration to take place faster. Since we did not use the fluted filter paper during the filtration some solvent evaporated resulting in premature crystallization and the solute stayed on the filter paper along with the impurities, making the percent recovered lower. The melting point obtained was 216.8-218.1