Friday, September 27, 2013

How to Jump Onto a Moving Train?!

Heating baking soda using a gas collection apparatus.
Starting over is always tough.  At the beginning of the new school year I was struggling to find the right entry point into the study of chemistry for my students.  I decided to start with an experiment that requires fire, has glassware to assemble, and generates graphable data.   I had the kids decompose baking soda by heating it in a Bunsen burner.  Although this sounds very simple, it turned into a rich experiment to launch my lab-based curriculum.

I found my inspiration for this experiment from the IPS book (Introductory Physical Science - 8th edition by Uri Haber-Schaim).  The opening experiment in this inquiry-based physical science program is to heat baking soda.  As I read through the teachers guide for more details, I came across this statement:  "The original mass of baking soda doesn't matter, more baking soda will increase the volume of gas produced."  That's when I decided to make this into a controlled experiment with an independent variable and dependent variable.  This simple experiment can be easily manipulated to collect enough data to explore the relationship between the mass of baking soda used and the volume of gas produced.

On the first day of experiment, I taught all the students how to light and extinguish the Bunsen burner.

Gas bubbles can be seen in the inverted bottle.
 Once the jitters were out of the way about using the flame, we launched our first round of data collection.  To start off, I had all the students measure out the same mass of baking soda.   I took time to demonstrate how to assemble the apparatus, and then checked each group's set-up before they began heating the baking soda.  I love experiments with apparatus to assemble. This may be the only place in their technology-rich lives that these kids screw a ring clamp to a stand and tweak a tube so that gas bubbles come out inside a bottle.  At the end of the first day, every group could answer to the original question: What happens when we heat baking soda?

Each group used a different mass of baking soda in the second trial.
One the second day, I posed the idea of creating a controlled experiment based on what we had learned about the system.  Through a class discussion, the students generated a question to answer through experimentation.  Once they all agreed on the experimental question:  "Does the amount of gas produced change if we vary the amount of baking soda", each group chose a different amount of baking soda to decompose.  As a class, my students generated a set of data that could be used to formulate an answer to this question.  We plotted a graph of the data, and it gave us a very nice linear trendline.  Now, I have to admit that I was pleasantly surprised when we got a nice graph out of this experiment.  There was so much room for error in this experiment that I was pretty sure that our data would require a lot of handwaving and error analysis to make any sense.

I really enjoyed starting the year with this lab because it has so many introductory concepts all wrapped into one.  The kids learned how to light  the Bunsen burner, they designed and implemented a controlled experiment, they leaned how to measure the mass of a powder and the volume of a gas, they assembled apparatus to collect a gas, they plotted a graph of their data, and answered an experimental question.  I call this a home run in the first week of chemistry class.
A graph of my class data, not bad for the first experiment of the year.


  1. How did the students find the volume gas on the unmarked soda bottles?

  2. Hi Wesley. Here's how we did it: The students held the bottle upside down in the water trough to trap the gas produced at the top. They used the rubber band to mark the hight of the gas. Then they filled the bottle up to the rubber band mark with water. At this point they transferred the water into large graduated cylinders to measure the volume. Although there is a lot of error in this method, the students fully understand the technique.

  3. Hi, really nice to see you guys doing this, actually i came here to get some help & i would like to say thank you for posting this. But here I see a problem with your setup, the problem is your rubber tube is not near the bottom of the inverted tube, its half way in the water, which actually will cause some of the gas produced to dissolve in water resulting in less volume of gas generated. Anyhow for this activity you might not see it, but when you do same in later chapters you will see the difference.

    Muhammad Junaid Arshad