Every year from day one I always have first years asking when can we blow something up. A lot of primary school teachers are putting a lot of effort into their science classes and the kids arrive expecting big things from big school. This year was no different, especially after showing them how the gas taps & Bunsens work.
"Sir can we blow something up?"
"Can we burn something"
"Let's do an experiment with fire"
My usual response is to distract them with other experiments that were prescribed by the old curriculum, not very innovative, but it's what I did.
This year with the new emphasis on Nature of Science I said "sure, why not", but before we did anything the students would have to prove there was scientific merit to the experiment. "Just to see what happens" doesn't cut it.
Over the course of the next few classes I gave 5-10 minutes to discussing possible options/ideas for experiments. Through group discussion we settled on vinegar and baking soda. A standard experiment that a lot of them had done in primary school, but I wanted them to take it further. Their homework that night was to research the science behind the reaction and think of what we could measure. During the class I had introduced the words quantitative and qualitative and explained the meaning behind them.
It took 5/10 minutes each from another two classes to settle on the design of the experiment, this involved very fruitful discussion on what we could measure (colour change, CO2 produced) how we could measure it (observation, circumference of a balloon) and what we would vary during the experiment (quantities and heat supplied). We discussed why it might be better for each group to carry out the same 2-3 variations of the experiment rather than everyone doing different ones, we examined the equipment available in the lab and tried to decide what we could use.
On experiment day I took quite a bit of control (they are first years after all) I decided the most accurate way to carry out the experiment would be the setup used for production of oxygen, but using a boiling tube with an arm instead of a Buchner flask.
I drew a diagram of the experimental setup on the board and got each group to come up and collect each piece of equipment as they needed it. We agreed to test 5g of baking soda with 10ml of vinegar first. We practised filling the graduated cylinder and placing it on the beehive shelf without any air inside, we practised stoppering the tube before we added the vinegar, having one student assigned pour and another assigned to stopper. We discussed what they expected would happen during the experiment and how they would read the result, most seemed a bit confused by this so I just decided to go for it.
I can't believe how well the experiment went, four of the groups ended up with roughly the same value for CO2 produced, some struggled with stoppering in time, others had spilled either the baking soda or vinegar during the process. I wrote all results on the board and got the average, we debated whether to include all results given things had gone wrong in some.
We then repeated the experiment but with 10g of baking soda and 10ml of vinegar. Almost all had an issue stoppering it quickly enough this time and all groups say a reduction in CO2 produced, but they saw from their tubes it was because a lot of baking soda was left over and they used the words "it hasn't all reacted".
I'm absolutely thrilled with the result and would definitely recommend it to others. Maybe not this exact experiment (although it does work nicely).