Exploring Chemistry

I’m liking the challenge and the potential impact of ‘exploring’ each concept before students actively study as I attempt to implement explore-flip-apply. My twist, though this is blatantly stolen, is to have the students reflect on &/or explain the exploration in a blog post.

My post is coming up prior to any data to support an assertion of actual improved outcomes and increased learning. However, the questions asked, exposing the interconnections between concepts, was absolutely amazing today.

WaterElectrolysisThe activity, using a 9-volt battery to eletrolyze water, is part of my first unit and I wanted it to both review and set the stage for stoichiometry. There were four questions I wanted them to answer:

  • What is the balanced chemical equation?
  • Is there qualitative evidence to support the balanced chemical reaction?
  • Could you collect quantitative data to ‘prove’ the balanced reaction? How?
  • Can you draw a particle diagram(s) that models what’s going on in this reaction?

I had the equipment out — battery, sample cups with tacks, small plastic test tubes, and two different salt solutions — and we got started. One of the first questions asked was how to capture the gas in the test tubes. This is not a question to be taken lightly, since the point was to have the captured gas push water out of the test tubes to visually see the difference in the amounts. Rather than let the students struggle, I made a mistake I think, I showed them what to do — fill the test tubes with the salt solution, invert, and quickly fill the sample container with more solution. The whole apparatus is now placed upon the battery. Immediately, bubbles begin forming, an unmistakable difference in rate apparent. The students get theirs going.

I wanted them to work alone to answer each question first, thinking about them while they watched the reaction, then using their ideas during discussion. Again, I think I jumped the gun a bit — struggling is not something they enjoyed — and I cut this time too short.

We jumped into the group discussion with the first question and a uniform response was provided, a balanced equation for decomposition of water. I jumped to the last question here, I’m leaning toward making it the second question next time, and, again, a confident reply of ‘sure’ from the group. The second question was the first divergence from my script: how can you know that the gases are actually hydrogen and oxygen? The observations also helped to push this question forward from left-field. After a bit, all the test tubes lost the apparent doubling of gas in one test tube versus the other; there was still more in one, but it didn’t look like twice as much. To try to show this, I introduced some UI to the solution and filled the tubes and sample cup again. One complication, the salt solution used sodium bicarbonate.

Shifting our focus again, during this time of waiting and watching, we jumped to the third question; surprisingly tougher than I thought. They were still focused upon how to measure the products, how to verify they were oxygen and hydrogen….I just wanted them to think how a balanced equation had to be based on an equal mass before and after. So, I kept trying to push them back to the law of conservation of mass, the law behind a ‘balanced chemical’ reaction. Again, I gave in, and just told them this.

Concluding the UI variation….

Gases are now being produced in a blue solution, but bless it, one of them begins to lighten (I won’t go so far as to say it turned yellow, but it did become less blue). This lead to what exactly this change in color meant. We take a turn into pH, the equilibrium of water ionization and baby steps to electrochemistry. Using the equilibrium equation as a new starting point, I try to encourage them to work out what’s ‘left’ when each gas is formed, pushing them to visually separate the equation in their mind and the bell rings.

I try to frantically throw information at them as they ready for the next class and assure them we’ll do a quick finish-up tomorrow, in class, and their blog post will be due tomorrow now, too.

[Follow-up: so quickly refocused upon goals from yesterday, added some explanation about self-ionization of water, rewriting the equilibrium equation twice. Without going into detail on redox, so just in terms of particles, if hydrogen is removed (or oxygen), seeing what is left behind helps to explain why the indicator changed color, why the pH is different. I’m really hoping this turns into a seed to reap from in future concepts.]

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