Week 8 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.
Administrative Issues
1. Please consult your teaching assistant directly in order to find out when a particular post-lab report is due. The yellow reader outlines the tentative schedule which has to be adjusted from time to time depending on how the section proceeds with the in-lab work.
2. If you have questions of general nature, please post them on the course discussion board instead of sending it to the instructor. Answering the same question several times is not productive for anybody.
3. The report for the project will be due by Friday, May 15, 2015 at 4:30 pm (in paper) and on the same day by 5:00 pm (on www.turnitin.com, CourseID: 10086582, Password: Chem30BL).
Prelab questions
1. After reviewing the chapter about "Polarity" and "Green Chemistry" in the reader very carefully, take the online quiz.
(http://bacher.chem.ucla.edu/TakeQuiz/?id=c74d97b01eae257e44aa9d5bade97baf). The quiz is worth 10 points, and has to be taken until one hour prior to the regularly scheduled in-lab meeting 8. Even though you can take the quiz until one hour prior to meeting 8 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 (Virtual 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 .
2. Reaction planning of esterification carried out in the lab
a. Which compound is used in excess in this reaction? Why is this approach necessary?
b. Why is it important to exclude water from the reaction as much as possible?
c. Why is it important to reflux the mixture properly? Which observations should the student make?
d. After the reaction is terminated, the mixture is chilled and then water is added. Rationalize this step.
e. The combined organic layers are extracted with saturated sodium bicarbonate solution. How does the student know that he is done with this step? Show pertinent balanced chemical equations.
3. A student refluxes a mixture of 3.25 g of salycylic acid, 5.00 mL of ethanol and 0.50 mL of concentrated sulfuric acid for four hours. After the work-up, the student isolated 2.54 g of the product.
a. Show a balanced chemical equation for the reaction.
b. Determine the percentage 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 nD24=1.5280. Which conclusion can he draw from this observation?
e. How many signals does the product exhibit in the 1H-NMR and the 13C-NMR, respectively? How do these signals look like? In which range do they fall?
4. Photochemistry Experiment (The extra credit
project 2 in the reader will be carried out as regular experiment this
quarter. Prepare a separate prelab for this experiment and turn it in to
your TA.)
Note: The student will start this experiment on
Thursday, August 27, 2015 or Friday, August 28, 2015. The work up and
characterization takes place on September 1, 2015 or September 2, 2015.
a. What is used as reaction vessel in this reaction? Where is it
obtained?
b. Why is it important to heat the mixture of benzophenone, acetic acid and isopropanol?
c. Why is the hot solution immediately transferred into the reaction vessel which is sealed immediately afterwards?
d. The student submits a sample for HPLC analysis. How is the sample prepared?