Monday, January 30, 2012

Baking soda reactions never get old

There's nothing like a baking soda volcano. What kid doesn't love to see all that weird white foam come burbling out of a paper mache cone?

What's that you say? Volcanoes spew lava and hot ash, and not the product of a baking soda/vinegar reaction? No one pours anything into a volcano to make it erupt?

I love that today's experiment captured the natural student excitement about the baking soda volcano but also taught them some accurate chemistry.

We started by reviewing what a physical change is, emphasizing that phase changes and mixtures such as solutions and suspensions are reversible. Then we talked for a bit about what kids thought a chemical change would entail. I introduced the definition, which I now have posted on our display along with other new words introduced in the past couple of weeks. Then we were ready for the experiment.

Students wrote hypotheses to respond to the question: Does baking soda react chemically with lemonade. Most kids instinctively said yes, but their reasoning was all over the place. This is understandable; so far we have only dipped our toes in the vast field of chemistry. Next we reviewed the procedure. Last week when we strained applesauce I was underwhelmed at how poorly the small groups followed directions when they strained the sauce through the coffee filter. I wanted to make sure that this time they understood expectations and successfully completed the procedure. I also gave them time to plan how to collect data without giving any directions. At the end of the lesson I collected and quickly assessed their work to make sure everyone knows how to plan for data collection. We are moving closer and closer to the point where they will plan and execute their own experiments, so it is my job to make sure they are able to do each step of the process.

Small groups stirred baking soda into water and watched it dissolve. Good review of solution making, and also our control for this experiment. And then the joy and wonder! Baking soda fizzing in lemonade! Could science be any cooler?

Kids recorded data, wrote brief conclusions and many also jotted down new questions they have. One area we need to keep working on is making sure that their conclusions respond directly to the question being tested. We reviewed their conclusions, and then I gave the five minute science teacher lecture about why the baking soda caused a chemical reaction. Later, when I read over their questions, I was pleased to see that many of the questions they had right after the experiment were wonderings about why the baking soda reacted, or what was in the lemonade that made it react. Exactly the point I wanted to raise for them, and hopefully my science talked cleared things up. (They did a great job with data collection, too. Most kids made simple charts, but one student created a Venn diagram and another did labeled sketches for each mixture.)

Last and most fun part of this lesson: I had poured glasses of lemonade for everyone and said they could choose to drink it plain or try it fizzy. Every single one of them wanted to try it with the baking soda mixed in, and they all loved it! Kids, you can try this at home! One student started asking me if there was baking soda in carbonated soda, another wanted to put more baking soda in a partially-drunk glass of fizzed lemonade to see if it would create another reaction. They are thinking like scientists...

My regrets that it all happened so quickly, I never got the camera out. Hopefully you were using your imagination as you read this, If not, feel free to go into your kitchen and stir about 1/4 tsp baking soda into a tall glass of lemonade and see for yourself the magic of what happens.

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