Week 7 Problem Set 30 BL (Esterification Reaction)
Useful Link: Refractometer
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. Reaction planning of esterification carried out in the lab
a. Why is it important to use an excess of the alcohol in this reaction? How much of it is used?
b. Why is it important that the glassware and the reagents are dry in this experiment?
c. The procedure asks to add a 1-2 drops of concentrated sulfuric acid to the reaction mixture. Why is this necessary? Show the appropriate key intermediate assuming salicylic acid was used as unknown acid.
d. The reaction mixture has to be refluxed. What does this exactly mean and how is this accomplished in the lab?
e. After the reflux period, the reaction mixture is chilled and ice-cold water is added. The student observes the formation of a white precipitate at this point. Rationalize this observation.
f. After extraction the mixture obtained in e., the combined organic layer is extracted with sodium bicarbonate. How does the student know that he is done with this step? Show pertinent chemical equations.
g. During the vacuum distillation, the procedure asks to apply a vacuum before heating the mixture. Explain briefly why.
2. A student refluxes a mixture of 4.97 g of salicylic acid, 4.00 mL of ethanol and a few drops of concentrated sulfuric acid for several hours. After the work-up, the student isolated 4.55 g of the product.
a. Show a balanced chemical equation for the reaction.
b. Determine the yield of the reaction. Show all calculations.
c. Predict the boiling point of the product at p = 50 torr.
d. The student observes refractive index of nD23= 1.5280. Which conclusion can he draw from this observation?
e. How many signals does the product exhibit in the H-NMR and the C-NMR, respectively?
3. After reviewing the UV-Vis chapter in the reader, take the online quiz
(http://bacher.chem.ucla.edu/TakeQuiz/?id=c20ad4d76fe97759aa27a0c99bff6710). The quiz is worth 10 points, and has to be taken until 1 hour prior to the in-lab meeting 7. (Hint: In some cases more than one answer is correct!) Even though you can take the quiz until one hour prior to meeting 7 of your section, you should not delay taking it since there might be some problems with the server. There seem to be problems with some MAC systems as well. After you submit the answers, your score should appear on your screen. If this does not happen, you will have to retake the quiz. (There will not be any possibility to retake the quiz weeks later!). In order to take the quiz, you have to go through a UCLA ICP address. This means that you either have to use your Bruin-Online account or go through the VPN (Vitual Private Network, software can be found here: http://www.bol.ucla.edu/services/vpn/) to have this UCLA ICP address. To log in, use your last name and your student ID. If you are experiencing problems, contact the instructor via email and include your full name (indicated which one is your last name), your student ID and section .