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ChemLab113-0049 - period swirl the beaker or stir the...

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Unformatted text preview: period swirl the beaker or stir the contents of the beaker with the scoopula for several seconds; that often produces a dramatic increase in the rate of crystallization by distributing seed crystals throughout the solution. While the aspirin is crystallizing in the ice-water bath chill 60 mL of distilled water in a beaker in a second ice-water bath. Use the filter crucible, a water aspirator and the plastic filter flask on your lab bench to filter the aspirin crystals from the reaction mixture. Your instructor will demonstrate that step. Afier filtering it is imperative that you remove as much of the liquid as you can before proceeding. Excess liquid is removed from the crystals in the filter crucible by pressing the water out with a glass stopper on top of a piece of filter paper, as your instructor will demonstrate. (It will not be necessary to press the excess liquid from the crystals after any of the filtering steps that are described below.) After that operation is done the remaining acetic acid is removed by washing the crystals with water several times. It is imperative to wash the crystals well to remove the acetic acid that is present in high concentration in the liquid left wetting the crystals. Significant acetic acid left with the crystals will have a disastrous effect on the results of the aspirin characterization to be performed in Experiment 5. Proceed as follows: Clean the reaction beaker to remove the acetic acid in it, and then transfer the crystals from the filter crucible to the beaker. Rinse the filter crucible and place it on the bench. Transfer the crystals back into the filter crucible, using a total of about 10 ml of your chilled, distilled water to help with the transfer. Put the filter crucible back in place, turn on the suction and pull off all the liquid. Now wash the crystals three times in the filter crucible as follows: Turn off the suction and set the filter crucible back on the bench. Add about 10 m1 of the 60 mL of chilled water, stir the mixture well for a second, and then quickly suction off the liquid. Follow the same procedure to carry out the two additional washings. If you and your instructor think the crystals still smell of acetic acid, wash them once more. After the final Washing and filtering you will dry the crystals well. Begin the drying by leaving the filtered crystals undisturbed in the filter crucible for ten minutes with the water aspirator on. Then lightly stir the crystals in the filter crucible for an additional five minutes, also with the water aspirator on. Finish the drying by spreading the aspirin evenly on a labeled watch glass and putting it in one of the ovens for thirty minutes. While the aspirin is in the oven, label your clean Na2C03 vial from Block I with your name, your teaching assistants name, and your section number. Weigh the vial on a top-loading balance, recording the mass in your notebook. Take the dried aspirin from the oven, grind it well to a fine powder using the mortar and pestle, transfer it to the vial, weigh it and record the mass. Store the vial of aspirin in your desicooler and return the filter crucible and mortar and pestle. Finally, take your data to the computer you have been using and follow the directions on the screen. 69 ...
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