Problem set #2 (Meeting 2)
Announcements
1. You are not allowed to use any readers in the lab starting meeting 2. All information that is needed to carry out the lab should be in your pre-lab report. No exceptions!
2. You will not be permitted to carry out any experiments without proper attire! This means if you do not show up in proper clothing or/and do not wear goggles and a proper length lab coat in the lab, you will be excused from the lab with a zero score (lab performance and quiz!) for this lab the first time (this means that you still will have to make up the lab later on without getting any credit for it!). The second time, the consequences will be more severe i.e. dismissal from the course for not following the safety protocol. CAL OSHA and similar offices have been inspecting the department and pass out very heavy fines (i.e. not wearing a lab coat or goggles costs more than $1000 which will come out of your bar account if you are caught by them!).
3. The IR assignment for this quarter is posted (link). The assignment is due by April 16, 2010 at 5:00 pm in the instructor's office in YH 3077E. Late assignments will not receive any credit. Assignments submitted via email will not be accepted. If you are not on campus on Friday, you will have to submit the assignment early.
ATTN: answers to the below questions are due at the start of meeting 2; these answers should be part of your pre-lab write-up. Show pertinent equations where appropriate.
1. Referring to the benzoin condensation, answer the following questions.
a. The procedure emphasizes to dissolve thiamine hydrochloride before adding 95% ethanol to the solution. Rationalize the procedure.
b. Afterwards sodium hydroxide solution is added to the mixture formed in a.. Show a balanced chemical equation for the reaction.What should the student observe here?
c. Then fresh benzaldehyde is added. The procedure emphasizes that the reaction mixture is homogeneous. What does this mean and why is this important here?
d. After sealing the flask the student places the flask in the drawer. After two days he returns to check on the progress of the reaction. Unfortunately, no crystals formed up to this point. What can he do to assist the reaction at this point?
e. After a week he returns to the lab and a copious amount of crystals formed. He isolates them using vacuum fitration. The procedure asks to rinse the crystals. Why is this necessary and what is used here?
f. A student starts with 0.20 g of thiamine hydrochloride and 1.5 mL of 0.10 N sodium hydroxide solution. Afterwards, he adds 1.9 mL of benzaldehyde to the solution. After the work-up, he isolates 1.60 g of white crystals. Determine the yield for the reaction. Show your calculations.
2. Vacuum filtration (will not be active before 4/2/2010 due to enrollment issues)
Please watch the following video (MP4-format) and read the appropriate chapter in the "Survival Kit Reader". Then take the quiz below.
Online Quiz
http://bacher.chem.ucla.edu/TakeQuiz/?id=c9f0f895fb98ab9159f51fd0297e236d
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, section and TA. (Hint: Think very careful about each response since many of the questions have more than one answer to them! Many students come up with the most obvious one and miss some of the details which leads to a zero score for the question!) Even though you can take the quiz until one hour prior to meeting 2 of your section, you should not delay taking it since there might be some problems with the server or the login. Also, there seem to be problems with MAC systems, Safari and Google Chrome Browser. The best is using IE 7.0 or Firefox. After you submit the answers, your score has to 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 since you are supposed to show preparedness at the point in time when you enter the lab!). The quiz is worth 10 points.
3. Referring to the elimination reaction, answer the following questions.
a. A mixture of conc. phosphoric acid and conc. sulfuric acid is used in the experiment. Which function does each compound have here?
b. What is the function of the Hickman head in the first distillation?
c. Why is important that the first distillation is performed slowly? What is distilled here? What is the boiling point of the distillate?
d. How is the crude product dried?
e. Why is it customary not to distill the entire crude during the second distillation?
f. The qualitative test that can be performed to verify the presence of an C-C double bond is the reaction with potassium permanganate. Show the pertinent chemical equation (including proper stereochemistry). What does the student observe in this reaction when using cyclohexene and cyclohexanol, respectively?
4. a. Using PC Spartan 2002 (which is only available in the SLC), perform the following calculations for the alkenes: terpinolene, limonene, a-terpinene, isoterpinolene. Make sure that all hydrogen atoms are present and there are also no extra ones either.
b. Select Calculations from the Setup menu.
The following window should appear. Select the options shown.
Verify that the Charge is Neutral and Multiplicity is Singlet. Click OK.
Select Submit from Setup menu.
Then click OK to exit dialog. Close the previous window.
Select Submit from Setup menu. When the calculation is completed you will be notified. It should not take more than a couple of seconds for the calculation to complete. Make sure that you have only one window open at this point. The messages are usually displayed in the first window, and often not in the window you are working in at this point.
Under the Display menu, select Properties. Record the value for the Energy.
Data Analysis:
1. Based in the calculated trends in the heat of formation (=energy), which alkene appears to be the most stable based on the calculation? How does this data match with the heats of formation given on page 21 (which are the experimental data)? Can you rationalize the differences?
2. Can you explain the product distribution observed for the elimination of water from a-terpinol (see reader page 20)?
3. Which conclusions can be drawn from this simulation? (Hint: Is the used computer model suitable to predict the outcome of the elimination experiment?)
Problems with calculations: Check here