F09Mid-term What to expect

F09Mid-term What to expect - What to Expect on the CHEM 232...

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What to Expect on the CHEM 232 mid-term exam, scheduled for week of October 26-30 The exam is a 10 question multiple choice exercise covering Expts# 1-5, worth 50 pts, or 5 pts per question. There will probably be two questions per experiment, one of which will be the sort of thing you did in the experiment (ie. problem-solving using data provided or analysis of data) and a second requiring demonstration of the principle(s) behind the experiment (ie. the kind of questions asked as post-lab questions where you apply what you learned from the experiment). You will have ~40 minutes to complete it. In general, specific details of what you did are not tested; but broader ideas like figuring out if a molecule is polar or non-polar and therefore what kind of solvent it will be soluble in; whether it will adhere to a silica TLC plate and therefore how large its Rf value would be; whether it will adhere to an alumina column and therefore how fast and in what sequence it and other components will elute from the column will be. FYI: It is important for you to recognize that the mid-term and final exams are ways to distinguish between those students who really understand what the point of the experiments performed was and how they relate to material addressed in lecture, and those who don’t. Based solely on lab reports, where many reported answers earn most, if not all, credit because of communal input and/or TA assistance, 90% of students would have the essentially the same grade, despite dramatically different comprehension and mastery of the course content. When finished, you will perform Experiment 7, GC analysis of fractions from distillation will be performed. An absolutely invaluable aide to understanding how this will be done is a video featuring Dr. Friedman, accessed at: http://chemlife.umd.edu/itg/ats/video/gc It will be posted on the BB homepage; you should view it before the lab so you know what to expect and therefore will be best able to complete the experiment in the time remaining after the mid-term. There will also be a pre-lab on GC. FYI: If you did not get good separation in the distillation expt, do not fear: we will do GC analysis on other samples and you will get data to deal with. A document detailing how you will handle that data has been posted in the “Assignments” folder on BB, just following the Expt #7 Worksheet. Recrystallization: Know what makes a good recrystallization solvent: Favorable temperature coefficient: solute is essentially insoluble at room temp or below, highly soluble at temperatures below the solute melting point Impurities insoluble in the solvent at all temps or remain soluble at room temp (both will allow physical separation from desired solute) Low enough boiling point so easily evaporated from purified solute BP lower than the MP of the solute Solvent does not react with the solute How to assess general solubility of solute in a variety of solvents: In general, polar or
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F09Mid-term What to expect - What to Expect on the CHEM 232...

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