The lesson begins with a balloon demonstration. Before the students enter the room, I place baking soda (30 mL) into a balloon and vinegar into a clear water bottle. I then carefully place the balloon onto the bottle, being sure not to let the baking soda fall into the bottle. Once the students have entered the room and taken out their journals, I ask them to write down some initial observations about the bottle and the balloon. After the students have had a chance to write their observations, I lift the balloon and let the baking soda fall into the bottle. As the baking soda reacts with the vinegar, the balloon inflates. I ask the students to record the following in their journals:
What are your observations? Why did the balloon inflate? Which scientific principle describes this action?
As the students write their answers, I monitor what they are writing. Once the students are finished writing, I ask for volunteers to share their thoughts. When the students share their observations, I ask them to tell me whether the observation is qualitative or quantitative, as a way to continue using the vocabulary we developed in the previous unit. If the students have difficulty articulating the scientific principle, I ask them to refer to their flipped notes to locate the answer. When answering the prompt questions, many of the students write that air fills up the balloon. They also note that a powder substance, many of them write that it is baking soda, fell into the liquid. Some students failed to see the baking soda fall from the balloon, so their writing lacked that observation.
During this portion of the lesson, I review the flipped notes with the students. The students have had online access to the notes and were assigned to have viewed and written their Cornell notes the day prior to our review of the information.
I am careful to point out the differences between physical and chemical changes, as this is usually confusing for the students. I provide the students with examples as a way of modeling thinking about physical and chemical changes, then I ask the students to work in their groups to provide one example of a physical change and one example of a chemical change. When sharing their example, the students must provide evidence as to why they think the change is physical or chemical. Once they share their examples, we analyze them as a class. I also review the answers to the chemistry notes review with the students.
Before we conduct our physical and chemical change activities, I remind the students of proper laboratory procedures and discuss the chemicals we will be using during the lab activity. The students are partnered up and they take their Chromebooks into the lab to complete the lab sheet online. Once the students have their aprons and goggles on, they are able to begin working on the lab. (Lab safety first!)
While the students work, I move from table to table, completing a lab checklist about their work. I only have the students complete the open flame portion of the lab during this class period. That way they all start at the same point the following day. This also makes it easier to manage supplies, supervise (if/when needed), and observe the lab activities. The completion of this lab addresses NGSS - MS-PS1-2, which states that students should be able to analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
When there are five minutes left of class, I have the students begin cleaning up their lab areas. Prior to leaving, we briefly discuss their observations from the first section of the lab. I ask the students to describe what they noticed as the candle melted and I ask them if this is a qualitative or quantitative observation. Generally their answers will be qualitative, so I ask them to offer a possible quantitative observation they could have listed.