Chem 51LB Week 4. Winter 16

Size: px

Start display at page:

Download "Chem 51LB Week 4. Winter 16"

Simon O’Connor’
5 years ago
Views:

1 Chem 51LB Week 4 Winter 16

2 Announcements Post-lab reminder Answer only experiment-specific questions, but note how they relate to the general questions. You ll be writing your own specific questions soon! Answer in full sentences or paragraphs (depending on length of answer). Exception: Some data can be in tables for results. Don t forget to number for TA convenience! Include your name! (General life tip: Make grading easy for grader!)

3 Reminder: Spectroscopy Dry Lab The additional spectroscopy assignment on Sapling is open. DUE MARCH 4.

4 Questions?

5 Problem of the Day - For Mon Class Determine limiting reagent and theoretical yield. ANSWER CHOICES AA) benzyl chloride, 165 mg AB) benzyl chloride, 240 mg AC) benzyl chloride, 283 mg CD) sodium iodide, 165 mg CE) sodium iodide, 240 mg CF) sodium iodide, 283 mg

6 Problem of the Day - For Mon Class A pair of students has conducted a nucleophilic substitution reaction like the one you did in lab last week. After filtration they obtained only a tiny amount of crystals (less than 5% of theoretical yield). The students conclude that the unknown solution provided by the stockroom must have been bad and state this in their post-lab assignment. In her feedback, the TA suggests that there are several other possible explanations for the outcome. What other explanation do you think is possible AND how could the students have tested in lab to support this explanation? What tests could the students have conducted in lab to support their original conclusion of a problem with the unknown solution? Include the expected outcome of the test.

7 From Last Week...Strengths & Weaknesses? Water that was used to filter the product may have not been cold enough -a way to test this is to place the solution in an ice bath and filter using cold water to see if product appears; if product appears, then this means the water was not cold enough; if no product appears, then this means that there is some other reason for a low percent yield Student might have used hot water which dissolves the solid, resulting in a lower percent yield Or that they didn t know how to work the vacuum filter properly (e.g. loose assembly), so product went into filtrate. They could use a different vacuum filter with cold water.

8 A Potential Safety Issue! They might ve forgotten to cover the top of the condenser, where the solution inside the round-bottom glass could ve evaporated. To resolve the problem, one must place a stopper or cork in the opening of the condenser. What is wrong with this suggestion?

9 Last Week s Problem Which test/result outcome could allow the students to support their original conclusion of a problem with the unknown solution? (You may choose more than one answer.) A. Attempt to recrystallize the very small amount of product they obtained resulted in no recovered solid. B. TLC of the filtrate showed benzyl bromide present. C. TLC of filtrate showed one of the three potential nucleophiles present. D. TLC of filtrate showed one of the three potential substitution products present. E. TLC of filtrate showed benzyl alcohol present. F. Melting point of crystals isolated from initial filtration match melting point of one of possible products. G. Mixed melting point experiment of initial crystals with possible product standard did not change melting temperature.

10 What s Wrong? Is this TLC plate ok as is? If not, how would you fix the problem?

11 Problem of The Day - TLC Edition Students ran TLC plates in a series of different solvents but forgot to label them. Match the plate to the solvent mixture. A) 9:1 Hex/EtOAC B) 3:2 Hex/EtOAc C) 4:1 Hex/EtOAc D) 1:1 Hex/EtOAC

Preparation of Penicillins by Acylation of 6-Aminopenicillanic acid with Acyl Chlorides Week One: Synthesis

Preparation of Penicillins by Acylation of 6-Aminopenicillanic acid with Acyl Chlorides Week One: Synthesis Wear gloves during this experiment. Dissolve 1.05g of sodium bicarbonate in 12mL of acetone: