A Quick and Dirty Stoichiometry Lab...Differentiation and Inquiry?

What am I doing to help kids achieve?

How do I know when they are there?

What is the evidence?

There is a traditional stoichiometry lab I have done before that involves adding dilute hydrochloric acid to sodium bicarbonate, boiling off the fluid and then getting the mass of the sodium chloride. Students then can solve the percent yield for the sodium chloride based on the amount of sodium bicarbonate they use. It is not a bad lab, but having hot ceramic watch glasses with acid in them just makes me a bit nervous. I am not sure where I got this new lab I am about to share, but it has been one that has evolved over the years. It is quick, dirty, relatively simple and uses over the counter (mostly) materials, making it much safer than the traditional lab that I used to assign.

First we start with some over the counter effervescent cold tablets. The brand name is "Alka Seltzer". Students are asked, "How can you figure out the ingredient that makes the bubbles?" Students brainstorm questions which are all collected and recorded. Next, we start in on stoichiometry. Ultimately, students figure out that they need the balanced equations to solve this problem. The nice part about this lab is that there are many substances in these tablets, however, the bubbles seem to only come from the baking soda. Students are provided the question and as a class we work on safety, procedure, materials and data. It is eventually decided that students will use dilute hydrochloric acid to react a portion of the tablet. After the bubbles stop, they let the test tube sit in a bit of warm water for a few minutes to help drive off all of the carbon dioxide. It is important to slowly add bits of the tablet to the acid. students record the mass of the tablet and materials before the reaction and they record the mass of everything after. The only difference is that after the reaction, the total mass is less due to the escaping carbon dioxide. The mass of the carbon dioxide can be converted to moles. From here, students use the balanced equation to solve for moles of sodium bicarbonate and then grams. Students then are given the mass of an entire tablet and to solve for the sodium bicarbonate in a whole tablet. They are also provide with the amount of sodium bicarbonate the manufacture claims is in the tablet.

This lab can be used many different ways. A teacher can stress the inquiry part, designing an experiment, experimental versus theoretical results, dimensional analysis, stoichiometry, significant figures or balancing reactions. Depending on your class, you can pick which aspects you believe would be appropriate for your students. About ten to fifteen minutes are required to complete the procedure and collect data. Sometimes, students add too much of the tablet all at once and the test tube over flows. It is simple and easy enough to start over. Overall, it seems to be a relatively simple lab that can pack an educational punch on several levels. The nice part is that you can adapt the lab to best meet the needs of your students. In other words, it is a form of differentiation.

Ultimately, it is about our students. It is tough and exhausting. The other day, I saw a great sign. It was a drawing with a circle that said "Comfort Zone" inside the circle. Outside the circle was a dot with an arrow and the phrase said, "This is where learning begins." Let's have fun as we take on the journey to learn along with our students.......

Editor's Note - Responding to a request for a student handout, Chad submitted what he provides for students. You will find it in the Supporting Information below if you are logged in to your ChemEd X account.. 2/22/18