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. In this week's experiment a carboxylic acid is reacted with an alcohol to form an ester. In which ratio are these reactants reacted? Why is this ratio been chosen? Explain.
b. What is function of the concentrated sulfuric acid in the reaction? Show the appropriate key intermediate. How much should be used?
c. Why is it important that water is excluded from the reaction mixture as much as possible?
d. The reaction mixture has to be refluxed. Which purpose does this step serve? Which equipment is used here?
e. After the reaction is terminated, the reaction mixture is chilled and water is added. The student should observes the formation of a precipitate at this point. Rationalize this observation.
f. Why is the reaction mixture extracted with sodium bicarbonate during the work-up? Show pertinent chemical equations. How does the student know that he is done with this step?
2. A student refluxes a mixture of 1.22 g of benzoic acid, 3.00 mL of ethanol and 0.30 mL of concentrated sulfuric acid for four hours. After the work-up, the student isolated 1.20 g of a liquid 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 = 20 torr.
d. The student observes refractive index of nD25= 1.4980. 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 .