Class began with a brief review of where we left off yesterday with the Egg Lab, followed by students writing today’s steps of the experimental procedure. After being checked off for having written out the steps, students put on gloves and carefully rinsed their eggs and cups. They took the mass of their eggs (the “after water – 9/23” mass) and recorded it in their lab notebooks. Finally, they chose one of the offered liquids (distilled water, 30% salt water, 50% corn syrup, 10% dish soap, or canola oil) or used a student-supplied school-appropriate liquid. Liquid was added to the cup (enough to cover the egg) and the cups were scattered around the room for observation.
After adding the liquid, students shared out their egg mass data along with their selected liquid. The data were collated and will be available as an Excel file for analysis on Friday. The students then toured the room, making observations about the eggs after they had been in liquid for 15-20 minutes. During the last few minutes of class, students began thinking about how they would draw a model to represent the movement of matter across the cell membrane. Students also received a reading packet and are responsible for reading pages 76-80 before the quiz on Friday. Students were encouraged to look through the reading this evening and to come to class prepared with questions to discuss during class tomorrow.
We worked through the remainder of the Lesson 8 worksheet today, tracing copper as it moved through the copper cycle and learning about the Law of Conservation of Mass in the Lesson 8 PowerPoint. We concluded the class with a demonstration. Most students were familiar with the chemical reaction of adding vinegar and baking soda together (it bubbles!). Students looked up the chemical formulas for both reagents and we discussed the products that are generated from combining the reactants (baking soda and vinegar). Students learned that the products of the reaction are sodium acetate, water, and carbon dioxide gas. The following question was posed: If a known amount of baking soda and vinegar were combined together in an open container on a scale, what would happen to the final mass of the products remaining in the container on the balance.
For the experiment, 5 grams of baking soda were added to 59.6 grams of household vinegar (5% acetic acid in water) in a flask placed on a digital balance. After a few minutes, the reactants stopped bubbling, and the mass of the remaining contents in the flask were found to be 57.5 grams. Therefore, the difference of 2.1 grams (59.6 grams minus 57.5 grams) should be the mass of the carbon dioxide gas released into the atmosphere. Tomorrow, students will conduct their own experiments and be tasked with using our available technology to evaluate the Law of Conservation of Mass for a given set of reactants.