Diffusion Thorugh a Membrane Lab Follow Up

So I already complained about the set-up for this lab. I'm afraid it simply isn't worth the effort. It is on the one hand a cook-book recipe lab, a traditional approach to lab activities that I just don't care for. It is also overly complicated, consisting essentially of three parts, although only two parts are listed officially. But I'm gettting ahead of myself.

Let me list some of the issues.

1. Safety. Goggles, gloves. I guess this is always going to be an issue, what school has a steady supply of gloves for students? I used up all my gloves earlier this year. I tried to minimize any hazard by distributing the chemicals in dropper bottles to avoid spillage. Not enough goggles, so I had to keep reminding people without goggles to keep back from the materials, or switch and put some goggles on - then there's the hygiene issue...

2. Poor instructions. No way were my students going to make sense of the instructions. I had to demonstrate just about every step of the procedure and go over the lab sheets to help them fill it out. At least a cookbook lab should have instructions the kids can follow. I would definitely write a companion set of instruction for next year.

3. Space. Not that there isn't enough, but that the ameneties are inadequate. No sinks, no running water. No outlets for setting up waterbath. Clean-up was as much work as set up, since I could not have every group clean up their own station, since their stations don't include sinks or water. And just going through Part 1 took all of a double period (80 min) with almost no time left to discuss the results. I planned the lab for today when I knew my room would not be used in between my lab periods by other classes, otherwise I wouldn't have been able to clean up. If I were doing this lab again under these circumstances, it would be a demo lab. Sorry. I mean come on, seven test tubes & ten medicine droppers per group? Only one sink and it'a across the hall?

4. Complexity. I would have broken this lab down into at least 3 parts, three days. Part 1: Indicators. Part 2: Diffusion through a membrane, incorporating the indicators. Part 3: Osmosis in plant cells. I realize the idea is to learn about indicators in some sort of context, but this should not be the students' first introduction to indicators - there just isn't enough time to explore them. For example, one of the lab sheet questions asks students to suggest a way to demonstrate that it is the combination of Benedict's Solution and glucose that causes the color change - not just the Benedict's and not just the glucose. But there's no provision for actually testing it (I did as a demo anyway, of course). Likewise, students should have time to explore Lugol's solution with other materials.

Kick myself for waiting until now to do these labs, but maybe doing it this late will get them the extra points they need for the exam. I just hope that with all the graduation-induced haze, they don't go completely brain dead between now & the 22nd.

UPDATE

Final Thoughts on Part 2