Making CO2
Before making a water filter, we first need to understand some chemistry. The explorations below give students skills and knowledge they can apply to making plaster filters.
I. Baking Soda and Cream of Tartar
Baking Soda (Sodium bicarbonate) and Cream of Tartar (Potassium acid tartrate) can be combined to form a chemical reaction.
• Have students measure 1/4 teaspoon of each compound and mix in a clean dry container. Is there any reaction?• Add 1 tablespoon of water. What happens?
A chemical reaction between Baking Soda and Cream of Tartar releases carbon dioxide (CO2) and creates a new compound, Sodium Acetate (CH3COONa). The chemical reaction looks like this:
NaHCO3 + KC4H5O6 → K+1 + Na+1 + C4H2O6 -2 + H2O + CO2↑
Chemical Change
This chemical reaction is a chemical change. The compounds are changed because the connections between atoms is changed and the products look and act unlike the ingredients. This is different than making a mixture, for example. If you add sand and sugar, they may be mixed up and look different, but if you taste the mixture you can still tell that there is sugar unchanged in the mix. In the chemical reaction above, baking soda and cream of tartar are white powders to begin with, but then the products (C02, a gas, and sodium acetate, a salty/vinegary chemical used to flavor potato chips).
There are several sources of information to use to help students to be aware of the nature of chemical change. See the following science link for resources on chemical change: Chemical Change Resources. Although knowledge is important, experience is also critical. Students should have a good sense of how to measure chemicals, how to observe reactions, and how to record data. This would be an excellent opportunity to refresh liquid volume and solid mass measuring skills. It is also a good time to remind students to use the STEM Notebook for all their work.
II. One can collect the amount of gas generated from the reaction by setting up his apparatus:
Baking soda, water and cream of tartar are placed into the container at left. The gas created then passes through the tube, displacing the water in the inverted graduate cylinder. A simple measurement of gas volume may be read dependent on amount and proportion of reactants. This can be demonstrated and/or students can do their own set of experiments using small plastic tubs, aquarium tubing and a small plastic generating container.
Students can develop a theory on how much proportion of each chemical is required by repeating the experiment using different ratios:
1/4 tsp Baking soda + 1/2 tsp creme of tartar = . ________CO2 gas in ml.
1/2 tsp Baking soda + 1/4 tsp creme of tartar = . ________CO2 gas in ml.
1/2 tsp Baking soda + 1/2 tsp creme of tartar = . ________CO2 gas in ml.
If a triple beam balance is available, students can use gram measures to be more precise in measuring ratio amounts:
The combination that creates the most gas can help one detect the proper ratio needed for the reaction to occur efficiently. The question becomes, should we always use equal portions? Should baking soda be 2X that of cream of tartar? Or should cream of tartar be 2X that of baking soda? For students able to understand the actual formula above, the best formula is displayed in the chemical reaction itself.