216 F09-E2-key - 216 F09-Exam #2 Page 2. Name _Key_ I. (6...

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216 F09-Exam #2 Page 2. Name _____ Key ______________ I . (6 points) There are two types of filtration methods used in organic experiments. These are: (i) gravity filtration using a short-stemmed (glass filter) funnel and fluted filter paper and (ii) vacuum (or suction) filtration using, e.g., a Hirsch funnel and round filter paper to cover the inside bottom of the funnel. For each of the following experimental operations, suggest which of the two filtration methods should be used. (1) A step to remove insoluble impurities from a solution of a compound in hot solvent in the process of recrystallization of the compound: ___ gravity filtration __________________ (2) A step to collect crystals obtained by cooling down the filtered hot solution (see above) of a compound to room temperature: ___ suction filtration __________________ (3) A step to collect precipitates formed upon addition of aqueous HCl to the solution of the sodium salt of dilantin (Experiment 6): ___ suction filtration __________________ II . (9 points) In a number of experiments you performed in the lab, the product mixtures were extracted with diethyl ether a few times. The combined organic layers were first washed with water and then with brine. The resulting organic solution then was dried over a drying agent such as anhydrous CaCl 2 , Na 2 SO 4 , and MgSO 4 . Answer in the boxes provided the following questions. (1) (3 points) What is brine? saturated aqueous NaCl solution (2) (3 points) What is the purpose of this washing with brine? To reduce the amount of water dissolved in (diethyl) ether. (3) (3 points) Explain the chemical basis for the use of a drying agent? Use MgSO 4 as an example. Be specific if any chemical process is involved. MgSO 4 + 7 H 2 O MgSO 4 7H 2 O III . (5 points) Ethyl alcohol [CH 3 CH 2 OH] quite often is present in technical-grade diethyl ether. If this grade of diethyl ether were used, what effect, if any, would the ethyl alcohol have on a Grignard reagent produced? Explain in the box below using words and a chemical equation with phenylmagnesium
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216 F09-E2-key - 216 F09-Exam #2 Page 2. Name _Key_ I. (6...

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