practice1withkey - I Your Your Student Name: . 10# . Your...

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I Your Name: . Your Student 10# . Your TA . ceHlEM~Sl~V ~ (Q)(8)l f~IfD~1~ lE~alm version 1 Problem Score 1 (5 p) 2 (15 D) 3 (20 p) 4 (15 0) ·5 (15 p) 6 (20 p) . 7 (10 p) Total (100 D)
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Problem 1 (5 points) In each case, circle the correct option. a)' The normal boiling point during a steam distillation of a volatile, water-immiscible compound is always higher than 100°C. T I F b)A chromatography column using silica gel as adsorbent can be successfully run with solvents of decreasing polarity. T I F c) Ethyl ether (b.p. 35°C) is an excellent solvent for recrystallization. T I F d) In the isolation of caffeine from tea, calcium carbonate is used to make calcium salts of caffeine. T I F e) The measured optical rotation of a chiral compound is directly proportional to the sample concentration. T I F Problem 2 (15 points) Complete the following reactions. Do not show mechanisms. When more than one product forms, indicate which one is major. Indicate side-products such as H20. etc. when relevant. + Hel (c) methylene chloride + BrZ ethanol
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3 Problem 3 (20 points) a) Arrange the following compounds (I-IV) in order of decreasing At value on a TlC plate run with a solvent of medium polarity (please be clear when you indicate which compound would have the largest and which compound would have the smallest Af value). Justify your answer in no more than 20 words. (5 points) o o \I III IV b) A mixture containing three organic chemicals (A, B and C) has to be separated by column chromatography. Preliminary TlC analyses using different solvents gave the following results. Answer the following questions in the spaces provided. Try to limit each answer to no more than 20-25 words. (15 points) ~I .... ., B -~-$._" c@ .. _------~ methanol cyclohexane toluene i) Is methanol a good solvent to run the column? Justify your answer briefly. (5 points)
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ii) Which solvent or series of solvents would you choose to successfully run the column and isolate A, Band C? Explain briefly. {5 points} iii) Which solvent{s) would you choose to run the column chromatography if only compound A is to be isolated, and compounds Band C discarded? Explain briefly. (5 points) ----------------------~-----------------------------------~------------ Problem 4 (15 points) A sample of benzoic acid (11 g) was carefully recrystallized from water using the minimum amount of the boiling water (162 mL). The solubility of benzoic acid at room temperature is 0.29 g/100 mL. Calculate the % recovery of the recrystallization (disregard experimental losses).
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This note was uploaded on 09/15/2011 for the course CHEM 108l taught by Professor Palleros,d during the Fall '08 term at University of California, Santa Cruz.

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practice1withkey - I Your Your Student Name: . 10# . Your...

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