CHM 253L Organic Chemistry Laboratory I
Laboratory Follow-Up Assignment Exp. #3
Due:Wednesday, September 24, 2008 by 5:00 pm
Questions:
- Calculate your percent recovery by dividing the sum of the masses of all components by the mass of the preparation you were given. Calculate the approximate percent composition of your drug preparation based upon the total mass of components recovered. Do you think your numbers are reasonable? Why or why not?
- Report all melting point data and explain the utility of the information collected (what does it tell and what does it NOT tell you). Report the identities of any constituents that you could determine. If you cannot identify a constituent, propose a hypothesis as to what you think it might be and why. Do this for all constituents that cannot be determined with certainty.
- Describe and explain the possible effects on your results of the following experimental errors or variations. In each case specifying the component(s) whose percentage(s) would be too high or too low.
(a)After adding dichloromethane to your drug preparation, you didn’t stir the mixture long enough.
(b)During the NaOH extraction, you failed to mix the aqueous and organic layers thoroughly.
(c)You mistakenly extracted the dichloromethane solution with 1 M HCl rather than 1 M NaOH.
- Tell whether each of the following experimental errors will raise or lower the amount of product you recover, and why.
(a)You failed to dry the product completely.
(b)You used enough water to recrystallize phenacetin but your unknown was acetanilide.
(c)You did not extract all of the common analgesic from the dichloromethane solution during the NaOH extraction.
- During the NaOH extraction of the common analgesic, what chemical reaction occurred? Write a complete and balanced equation using Lewis structures to show this reaction. Later on, you needed to re-acidify using HCl. What reaction occurred here? Write a complete and balanced equation using Lewis structures to show this reaction.
- Acetaminophen is a weaker acid than your common analgesic, but a stronger acid than water. What problem would you encounter if the unknown component were acetaminophen rather than acetanilide or phenacetin? Be sure to indicate in your answer why acetanilide and phenacetin are not appreciably acidic and how this fact could influence your results.
Based upon what you learned in this experiment, how would you go about separating a mixture of methylenedioxymethamphetamine (free base) and o-chlorotoulene? Hint: you’ll need to consider the acid/base properties of the two molecules.