EXP2 - 1 Layla Fijany Chem 12A T/TH 5-10pm 9/5/2011...

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1 Layla Fijany Chem 12A T/TH 5-10pm 9/5/2011 Experiment 2: Crystallization Purpose : to purify a desired compound by crystallization and various filtrations techniques; learn how to choose the most appropriate solvent for a solute by taking into consideration solubility at different temperatures; calculate percent recovery; determine identity of an unknown compound using melting point technique and to determine purity of final material after crystallization by verifying the melting point of the sample Introduction: A common method for purifying solid compounds is crystallization (or recrystallization). Before starting the crystallization process, the most suitable solvent must be chosen in which the compound that is being purified is soluble at high temperatures (near BP of solvent) and insoluble at low temperatures. It is important to use as little solvent as possible so that the solution will be (almost) completely saturated. When the solution is heated to temperatures near the boiling point of the solvent, the impurities stay in solution (mother liquid) while the pure compound forms crystals. Therefore, the resulting crystal is a pure substance with little impurities. It is important to cool the compound slowly so that large crystals form, a sign of a pure compound. These crystals form because the solubility of the compound decreases as the temperature decreases. Once the solution has been cooled the crystals will be filtered from the solvent and impurities using various techniques. Determining the melting point and comparing it to a literature source may then verify the purity of the solid. Hypothesis: A suitable crystallization solvent will dissolve a large amount of the impure compound at temperatures near the boiling point of the solvent and crystallize the greatest yield of purified compound in the solution at low temperatures. Set Up: List of Reagents FW (g/mol) BP (˚C) MP (˚C) Density (g/cm 3 ) Other (hazards, uses, etc) Methyl Alcohol (CH 4 O) : 32.05 64.7 -98 0.7918 - reacts violently with acids, reducing agents, highly flammable; colorless, volatile, poisonous Ethyl alcohol (C 2 H 6 O): 46.08 78 -114 0.789 - volatile , flammable , colorless lqd; psychoactive drug in alcoholic beverages , also used in thermometers as solvent /fuel Diethyl Ether (C 4 H 10 O): 74.14 34.6 -116.3 0.7134 - colorless, volatile, extremely flammable lqd, odor; RI( n D Benzoic acid (C 7 H 6 O 2 ): 122.13 250 121-2 1.27 - clrless crystal solid; used as food preservative, inhibits mold, yeast & bacteria, also used to treat ringworm & athlete’s foot.
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2 Sulfanilamide (C 6 H 8 N 2 O 2 S): 172.2 ----- 165 1.08 - antibiotic, inhibits enzymatic rxns; very slightly soluble in cold water; harmful if swallowed or inhaled Flourenone (C 13 H 8 O): 180.2 342 83.5 1.13 - used to make antimalaria drugs; yellow flakes, chips or crystalline powder Toluene (C 7 H 8 ): 92.14 110.6 -93 0.867 - clear, water -insoluble liquid,
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EXP2 - 1 Layla Fijany Chem 12A T/TH 5-10pm 9/5/2011...

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