General Announcement (Please read!)

It has come to my attention that some students are not clear about certain policies in this course. There is no such policy in this lab course which discourages students from asking questions. The reason why you are here is to learn. This should also result in questions from the the student's side, which are welcome by the teaching assistants and the instructor. However, it is expected that the student comes prepared to the lab section in order to be able to complete the experiment in a timely fashion. The majority of the questions regarding the experiment (theory and practical issues) can be answered during lecture and office hours. A question generally should demonstrate the student's ability to analyze the problem and be as specific as possible in his/her inquiry.

ATTN: answers to the below questions are due at the start of your lab period; these answers should be part of your pre-lab write-up.

1. Referring to the reaction carried out in the lab, answer the following questions. Show pertinent equations where appropriate.

a. Why is absolute ethanol used for the reaction?

b. Why is it important to get the solution to a gentle boil before adding the KOH solution?

c. Which observation(s) during the course of the reaction indicate the progress of reaction?

2. Referring to the recrystallization step, answer the following questions.

a. Why is a solvent mixture (95% ethanol/toluene) used in this step instead of toluene?

b. Which problems does a student face if he boils the mixture used in the lab for a longer time?

c. Why is it important that the solution cools down slowly after dissolving the sample?

d. A student has 300 mg of the crude product. If the solubility of the crude is 40 mg/mL at 80 ^oC, 10 mg at 20 ^oC and 5 mg/mL at 0 ^oC, how many grams of the product would he recover if he conducts the recrystallization properly?

3. The student obtains the TLC for his final product.

stationary phase: silica mobile phase: methylene chloride:hexane (1:1)

a. Calculate the R_f-values for all compounds.

b.What can be said about the purity of the final product?

c. What would change if the student would use i) only hexane ii) only methylene chloride as the solvent?

d. What can be said about the relative polarity of the compounds?

4. A student has to obtain the UV-Vis spectrum for a compound that contains a keto function. The literature reports the following peaks: 280 (1500), 440 (4000), 590 (300). He is asked to measure the range from 200 to 600 nm. (Note: The number in parathesis are the molar extinction coefficients)

a. Which concentration(s) should he use in order to determine the molar extinction coefficient for all peaks in this range?

b. What does he have to consider when he acquires the spectrum?