One of the reasons I like guided inquiry labs is it inspires my students to ask more 'What if...' questions. I tried a new lab this year for Stoichiometry in which the students mixed different amounts of baking soda with vinegar. A balloon was placed on the top of each test tube and the students got a great visual for the amount of gas produced.
One group finished the lab and I noticed they started to fill another balloon with a very large amount of baking soda. When I inquired about what they were doing, they said they wanted to figure out if they could pop a balloon only using baking soda and vinegar. With wry smile, I told them they could do it, but only if they showed, using Stoichiometry calculations, how much vinegar they would need based on the amount of baking soda they had already weighed out (28g).
After some Internet research and a bunch of calculations later, they figured out they needed nearly 400mL (for the non-chemistry folks, that's A LOT) which is more than would fit inside their 25 mL test tube. I happen to have a giant test tube and the experiment was off.
Here is what the face of an engaged learner looks like:
The balloon didn't pop, but it got really close. When doing these labs, sometimes you just need to let the students' run with their ideas. It's amazing what they will come up with and what they will learn (about science and themselves) in the process.