Lab_Practical__1 - Chemistry 251 Laboratory Practical 1 For...

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Unformatted text preview: Chemistry 251 Laboratory Practical 1 For the next two weeks you will be carrying out the first of two laboratory practical exercises in Chem 251. In this experiment you will receive from your TA a fixed amount of isopentyl alcohol which you will use, along with some acetic acid, to make the ester isopentyl acetate (also known as isoamyl acetate). isopentyl acetate Acetic acid lsopeniyl alcohol The sample of the alcohol you will be given contains a small amount of an inert solvent so that you will not know how much alcohol you will actually be starting with. It is very important, therefore, that you immediately record the unknown number of your sample in your notebook so that your results can be graded properly. For the purpose of any calculations you might be asked to carry out, you should assume that your sample contained 12.0 gms of the alcohol. Procedure: Your entire alcohol sample should be mixed with 20 mL of glacial acetic acid (a two to three fold excess) and ~1—2 mL of a concentrated mineral acid to act as a catalyst. (Concentrated HCl, HNOa, and H2804 are all available in the lab - the choice is yours). This mixture should be refluxed for about an hour. After cooling, you will need to “work-up" the reaction mixture to separate and purify the isopentyl acetate ester. Your final result should be turned in to your TA in a clean, dry, screw—cap vial that is clearly labeled with your name, your unknown number and your TA‘s name. In order to receive any credit your sample must consist of a single phase which is both clear and colorless. Your grade will be based on both the yield and purity of your sample as determined by Gas Chromatography. You will also receive a grade for your notebook pages (your "work-up" procedure) which will be worth three times the normal notebook grade (3 x 100 points). While you will obviously model your procedure on the one used in the synthesis of methyl benzoate there are a few important differences. For one, the scale of this esterification is significantly larger and you will need to adjust your procedure to account for the increased volumes. Another difference is that you will be using (diethyl) ether as the extraction solvent for this experiment (instead of methylene chloride). Any other differences andlor changes are for you to discover. Hint: Be sure that you understand the nature and purpose of every extraction step used in the methyl benzoate ester synthesis before you begin to work on your procedure for this experiment. Also, be sure you read over the ground rules for laboratory practical exams on the reverse side of this handout. Chemistry 251 Laboratory Practical 1 ground Rules for Chem 251 Laboratory Practicals: 1. Discuss this "examination" as much as you wish among yourselves before you come to the laboratory. You must bring to lab with you a clear, carefully outlined laboratory procedure for the ENTIRE experiment This will be collected before you begin the experiment. This procedure should also include provisions for waste disposal. 2. The TA's are NOT to discuss any aspect of the procedure with you at any time, either before or during the laboratory. You should not approach any TA with a question about the experiment unless it pertains to safety or other non-procedural issues. 8. During the examination, there should be no discussion relating to procedures among yourselves or with the TA. This does not mean that you cannot talk with each other - but you should not be modifying your procedure based on something you saw someone else doing (or not doing). Have confidence in yourself and your procedure. 4. The TA‘s will answer ONLY questions relating to logistics (i.e.. "Where is the ethanol?") or safety (e.g., "Is it safe to use a bunsen burner here?"). 5. If you have any questions that you feel should be answered even if they violate the above rules, feel free to ask the Dr. Russo about them. He will be the sole judge as to any exceptions to the above rules. (You may of course freely ask any questions about the methyl benzoate experiment to the TA's andlor the Professor at any time). 6. There are no hidden tricks in this separationlpurification. It is based on theory that has been covered in lecture and on techniques you have been practicing all semester. ...
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This note was uploaded on 02/25/2009 for the course CHEM 2510 taught by Professor Russo,s during the Fall '07 term at Cornell.

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Lab_Practical__1 - Chemistry 251 Laboratory Practical 1 For...

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