Almost half my class stayed until the end of the period. Divide your class into three sections and have them each start with a different part of the lab to keep lines down.
Part A - PETE
The phthalic anhydride should be weighed on the analytical balances while wearing gloves. The cover should be closed as soon as a student is finished weighing. Make sure the students use the disposable culture tubes and weigh boats on the back benches instead of test tubes from their drawers. When heating polymers, use Bunsen burners angled into the hood making sure not to heat the clamps. There are matches under the chalkboards and extra hoses and glass hose connecters at the stockroom window to make the burners reach to the fume hoods. Many students needed help figuring out how to adjust the air/gas ratio on their burners. When the liquid turns a light amber color, they should stop heating and pour into a weigh boat within 10-30 sec (not the 30 sec - 1min mentioned in manual). If they pour their polymers at different times, make sure they observe the viscosities well enough to compare. All waste goes in the trash cans.
Part A - PVA films
Most students are confused about using the triple beam balances. Have them 'tare' their weigh boats (about 5g), and then add 15g for a total of 20g of weight. They then slowly pour in liquid until the arrow points to the line at the zero point. Watch out for students pouring excess liquid back into the bottles. They should dye each sample a different color and record this in their notebook so that when they cut their polymer away from their labeled boats next week, they will be able to distinguish them. They should remove as many bubbles as possible, or at least push them to the side so that they have a large section with no bubbles for testing next week. The boats should then be placed flat in their drawers to dry.
Part A - PEO demo
Do this 1 or 2 times per lab period. We had one TA stand on a stool and demo for all three sections at a time. To cleanup, pour the polymer into the waste container, add water, stir and pour into waste container again. Then use copious amounts of soap, water and brushing in the sink to remove the rest of the polymer.
Part B - Density
There is no PVC in the jars. Make sure the students do not shake or tip them too much. If you've never seen these before, go look at the colors and make sure you can identify all of the pieces because I always get a lot of questions about the difference between the blue and purple pieces.
I received lots of questions about Q5 because I did not discuss the definition of "cross-linking" in my prelab, which I will definitely do next time.