On September 15, we started Lesson 2-3 of The Garbage Unit. This lesson develops the idea that solids and liquids are made of particles and uses this idea to explain sugar dissolving in water. The day before this lesson, students made predictions about what happens to sugar when we dissolve it in water. Most students believed the sugar was still there because they could taste it in the water. Some students said that it was not still there because it disappeared. I asked them how they could gather evidence to determine if the sugar was still there. They suggested tasting the water. I reminded them of our prior investigations that used weight as a property and asked how we could use weight to see if the sugar was still there. Some students suggested that the weight could be evidence.

On the first day of this lesson, students investigated mixing sugar into water. They measured 50 ml of water and weighed the water. They weighed a spoonful of sugar. Then they mixed the sugar into the water until it dissolved. They weighed the mixture. While students were following directions and making their measurements, I circulated the room. I noticed that some students were getting erroneous data because they were not taring the scale correctly. I helped three of the six groups collect a second set of data to ensure they would all have accurate data to use to answer the four questions. If (I had not done this, they would not have noticed that the pattern that they need for later— that the weight of the water and the weight of the sugar add up to equal the weight of the mixture.)

Students answered four questions about the investigation with their groups. I collected the papers to see their thinking. One issue I noticed was that many students did not understand the concept of volume. When asked what happened to the volume after the sugar was mixed in, most students used the weight data to answer the question, rather than thinking about the amount of liquid in the cup.

I filmed a demonstration of the investigation to show as a review the next day to ensure all students could make the observations they needed.

The next day, I returned their investigation papers and we talked about volume. This is an important idea that they need to explain in their models.

We talked about the marks we made on the cup to show the amount of space the liquid takes up, or its volume. First we marked the level of water, then we made a new mark for the level of the mixture. We decided that the volume did not change much, it increased a small amount. How could this happen? We needed to figure that out.

The second day focused on developing a particle model of matter. Students read a short article called What is matter made of?

Then we discussed what we learned from the article. Solids and liquids are kinds of matter that are made of particles. All matter is made of particles.

Next, we watched a video that showed a physical model for particles and discussed the model. In this model, ping pong balls were put in a beaker.

Then marbles were added to the same beaker. The marbles fit in the spaces around the ping pong balls.

Adding the marbles to the cup did not change the volume much. We explained how the ping pong balls were like the water particles and the marbles were like the sugar particles. The water particles have empty space around them like the ping pong balls do. The smaller sugar particles can fit in the empty spaces like the marbles fit around the ping pong balls.

Students worked with a partner to talk about their ideas. Then they each completed an exit ticket that asked how the particle model could explain why the volume did not change much when sugar was added to water. I collected the exit tickets and found that many students only represented the sugar as particles, but not the water.

On the third day, we will review the information we have about mixing sugar and water. We have three sources of information—investigation findings, the reading, and the physical model in the video. I made a video to recap.

We will create our own system models that use particles to provide a cause and effect explanation of what we observed in the investigation. Students work collaboratively to create models using Google Slides. I made a template with a fixed background of the cup and spoon. Students can drag the particles to show how they are arranged. They create before and after models and write their explanations on a third slide.

https://docs.google.com/presentation/d/1C-34w4c3mogfO2IO0WmLgVH6tvIRNpeF9SwuE5XIGv8/copy

In this lesson, students are using four crosscutting concepts together as they generate their explanation for the phenomenon of sugar mixing with water.

• 3-5-CCC1.3: Patterns can be used as evidence to support an explanation.
• 3-5-CCC2.1: Cause and effect relationships are routinely used to explain change.
• 3-5-CCC4.2: A system can be described in terms of its components and their interactions.
• 3-5-CCC5.1: Matter is made of particles.

Students are also using several science and engineering practices

• 3-5-SEP2.4: Develop and/or use models to describe and/or predict phenomena.
• 3-5-SEP4.2: Analyze and interpret data to make sense of phenomena, using logical reasoning, mathematics, and/or computation.
• 3-5-SEP5.2: Describe, measure, estimate, and/or graph quantities such as area, volume, weight, and time to address scientific and engineering questions and problems.
• 3-5-SEP6.2: Use evidence (e.g., measurements, observations, patterns) to construct or support an explanation or design a solution to a problem.
• 3-5-SEP8.4: Obtain and combine information from books and/or other reliable media to explain phenomena or solutions to a design problem.

The lesson focuses on one disciplinary core idea

• PS1.A Structure and Properties of Matter
  • Matter of any type can be subdivided into particles that are too small to be seen, but even then the matter still exists and can be detected by other means.
  • The amount (weight of matter) is conserved when it changes form, even in transitions where it seems to vanish.