26 November 2007

A Better Mousetrap

Do you ever have one of those "Duh." moments? The ones that are slightly embarrassing to admit? I had one today...and yes, I'm revealing it here for all the world to read---because I want other biology teachers to benefit from my revelation.

There is a lab that I have often done with students. You take three different solutions (water; yeast and water; yeast, sugar, and water) and place them in test tubes. There is a rubber stopper with the glass tube and some rubber tubing that lead from each test tube into a smaller test tube containing bromthymol blue, an indicator for carbon dioxide. The experimental set-up is represented below:The idea is that you're able to look at evidence of cellular respiration because the assembly with the yeast, water, and sugar will turn the bromthymol blue yellow. It's great, except there are always some problems. It's darned hard to get all the tubes to stay connected and upright. If you have more than a couple of classes, you struggle to have enough materials. Keep in mind that the experiment runs overnight, so it isn't as if you can use the same things for each class. Meanwhile, the length of the experiment means that there is ample time for things to get knocked over or otherwise screwed up. The tubing isn't always clean and so results can also be iffy. More than once, I've played the role of the "carbon dioxide fairy," and used a straw to blow in some carbon dioxide before the students arrived.

So, it's that time again. I'm thinking about this lab, and while I want to use it...it's a lot of trouble and the issues with the design get in the way of The Big Idea. There has to be a better mousetrap, right?

At lunch, I mixed up some yeast, water, and honey. I put some in 2 test tubes along with bromthymol blue. I covered one and left the other uncovered (just in case the whole rubber stopper thing was important). In a third tube, I put bromthymol blue and then inserted a pipette that contained the yeast solution (in case separating the yeast from the indicator was important).

Wouldn't you know it? They all worked. And what's more, the two where the solutions were directly mixed only took 15 minutes to show results. The third tube took longer, but the indicator was yellow within 2 hours. No rubber tubing. No glass tubes. No rubber stoppers. No test tube racks overflowing and falling over with stuff.

I could have been doing this for years, saving myself a tremendous amount of headache and heartache...but no. The answer and materials were in front of me all along and I just didn't look for it. I am glad that I have now, and while I feel a bit foolish for not making this discovery before, I hope that others can learn from this.



Hugh O'Donnell said...

Hey, if big-time scientists can cook results for the current administration, why can't you make sure a cinch experiment turns out right? Right? ;)

Just kidding.

Do you have any insights I could use at the next school boundary discussion meeting? The amount of carbon dioxide blown over people at those meetings would make Al Gore blush.

Hugh aka Repairman

The Science Goddess said...

Sorry, but hot CO2 isn't part of our investigation. :)

Mike in Texas said...

I had a moment like that a few weeks ago.

I was going through the water cycle with some 4th graders and was boiling water on a small hot plate. Above it I had rigged up a rube goldberg device to try and capture some of the steam, have it cool off in some tubing, and eventually drop down into a measuring cup as precipitation. I think I may have captured one or two drops.

Finally it occured to me that all I had to do was put a one gallon glass jar over the hot plate and boiling water and I'd immediately have condensation and precipitation.

It only took me 5 years of being a science lab teacher to figure it out.

The Science Goddess said...

I think that the people who write these activities as part of teacher resource material have not actually done the experiments themselves. Or, perhaps, it has been so long since they tried them that they haven't thought that there might be possible improvements.

Linda Fox said...

Thank you. I teach in a class not set up for experiments, and getting usable chemistry experiments for the physical science class can be a challenge