last updated
Problems Set #6
General announcements (please read them carefully since you will held responsible)
1. In-lab work
It is imperative that students come much better prepared to the in-lab meeting. Many students seem to struggle performing the experiments in a timely fashion, in some cases due to the lack of equipment (nothing we can do about this at this point), in most cases due to simple mistakes and/or lack of organization skills i.e., setting the priorities straight (Hint: Cleaning every piece of glassware in your desk should not be your priority!). The lab section ends at 5:00 pm at the very latest and if you are not out of the lab by then, you will receive a significant deduction in points for your in-lab evaluation. Student will not be allowed to attend other lab sections, which means that they will not be able to complete the project. The experiments can be completed in the allotted time if you show up prepared and focus on your work.
2. Waste management and lab safety
a. The instructor noticed that some students poured acetone down the sink, which is entirely unacceptable according to California Law. If the authorities notice this, we will get fined $$$$.
b. Gloves and paper towel belong in the regular trash and not into the box where glass waste is collected. Students tend to throw the hot glass waste (from pulling capillaries in there and the paper might catch fire!). On the same token, glass waste and syringe needles belong into the blue-white box or the sharps container, respectively, and not into the regular trash can.
c. You are not allowed to wear gloves outside the lab. This applies in particular to the office suite in which the instructor resides since this poses a significant health risk for everybody in the suite. Another bad habit is to bring solutions and chemicals to the instructor's office, which is a no-no as well.
3. Quiz 3
The third quiz will be administered on Thursday, October 23, 2014 at 11 am covering the epoxidation (experimental and theory). Please make sure that you show up on time, which means at 10:55 am. Otherwise you will not be allowed to take the quiz. It would also be helpful to do some more serious studying as well.
4. Formal report
a. Make sure that you make progress on your formal report as well in terms of literature research and writing the parts that you completed already in the lab. The draft version of paper is due on October 17, 2014 at 4:30 pm. The draft version is worth 20 points, the final paper 60 points. For more information what the draft is supposed to contain see here. Late submission will receive less credit. The more of your work you submit here, the more feedback you will get, which will beneficial for the final version. We will try to return the reports by Monday, October 20, 2014.
b. The draft has to be submitted in a report cover. Copies of all spectra have to be included into the draft.
5. Data sharing
It also came to the attention of the instructor that some students are sharing data. To make it very clear, this is not allowed and will be regarded as cheating independent from what the teaching assistant told the students. This also means that the spectra have to be properly labeled i.e. the title and name of the student have to be printed on the printout and not be handwritten.
6. Experimental
a. The solvent level in the NMR tube has to be as accurately as possible 5 cm. The solvent here is CDCl3, which can only be handled in the hood and with nitrile gloves.
b. The NMR tube has to be properly labeled (unknown, student name, section, Chem 30CL) and also be signed in with the same information.
c. The GC sample has to be signed in as well (student name, unknown, etc). Samples that are not properly label or signed in will not be run. The solvent here is hexane and not CDCl3! The label of the GC vial has to have the unknown on it as well!
ATTN: answers to the below questions are due at the start of your lab period of Meeting 6 (10/21 or 10/22); these answers should be part of your pre-lab write-up.
1. Flash chromatography
a. Silica is used as stationary phase. Which problem(s) do arise from this choice?
b. Why is it important to use sand when packing the column? Where is it placed?
c. Which solvent should be used to wet the column? Rationalize your choice.
d. Why is it crucial that the stationary phase is properly pre-treated with a 1 % solution of triethylamine?
e. A student acquires the TLC for the fractions 2, 5 and 8. He observes two spots at Rf =0.35 and Rf =0.80 in 2nd, one spots at Rf =0.34 in 5th fraction and one spot with Rf =0.20 in 8th fraction. How should be proceed? Explain.
2. NMR spectroscopy
a. Why is it important that the NMR tube is dry before placing the sample in it?
b. Which solvent is used to prepare the NMR sample? Which precautions have to be taken when using this solvent?
c. How much solution should be placed in the NMR tube (exact height!)?
d. What has to be included into the label on the NMR tube? Where this label placed?
3. GC/MS chromatography
a. Which solvent is used to prepare the solution to be submitted for GC/MS?
b. What is the proper concentration of the sample to be submitted?
c. Which other aspects have to be considered when preparing and submitting an GC/MS sample?
d. Which information does the student obtain from the GC/MS data?