LONG lab today! My last students finished 30 minutes after lab was technically done. Be prepared to warn them that the lab is long - especially if they didn't do their theoretical yields for the CaCO3 from two weeks ago, or if they did it incorrectly.
Here are some thoughts to help lab #8 move along:
* They will check out a Molarity Kit from window, one per two students.
* Assign partners different colors of dyes so each has to do their own dilutions
* One partner can set up dilutions while the other uses the buret, volumetric pipet, and pH meter
* Go over how to do the dilutions step by step - a drawing on the board helps
* The post lab questions are good, but go back and review old stuff (like total ion calculations) so there were many confused students on those.
* By the time the second student was using the pH meter we had problems with getting those calibrated. I think you need to make sure that they turn off the pH meter before re-running calibration. But turning it off can be tough - there were several that I had to repeat the "off" sequence several times before they would actually shut off. And some I couldn't get to recalibrate at all.
The main issues with finishing the CaCO3 lab were
* Students have forgotten how to do theoretical yield calculations
* Actual yields again ended up high in some cases.
* Filling out the observation part could be consolidated into one overall diagram showing which cells had a precipitate
Overall - Finishing the CaCO3 and doing Experiment #8 parts I and II is probably too much to all be finished in one lab period. Last fall we only did Part I so that would be plenty of time, but with all the finicky measurements in Part II we ran over.
Good luck and move them along!