In this two day lab rotation, students go through a series of engaging lab stations that cause the students to discuss their conceptual understanding of density. Students work on group discourse as well as density calculations as the complete the lab stations.
MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MS-PS1-4 Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
CCSS.ELA-LITERACY.WHST.6-8.1.B Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.
CCSS.ELA-LITERACY.RST.6-8.3 Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.
Science and Engineering Practices:
In this lesson, students utilize mathematics and conceptual thinking as they calculate density and answer questions that cause them to think conceptually about density (SP5). Students also answer lab questions that ask them to engage in argument based on evidence through group discourse (SP7). As students discuss ideas and evidence with their groups, they also work towards obtaining information and communicating their scientific understanding (SP8).
Relating to the NGSS, students look for the relationship of adding and removing heat and the physical properties of mass, volume, and density. Thus, this connects to the Cross Cutting Concept of “Patterns” which explains that macroscopic patterns are related to the nature of microscopic and atomic-level structure.
Ask the students, “What are you going to learn today?”. Students should respond with the Essential Question, “How can the arrangement and motion of the particles in a substance affect its physical properties and how can they be measured?” I keep this EQ posted on the board and students also have a copy of it in their Density Unit Plan.
Let students know that today they are going to be introduced to Skill 1:
D.1 I can provide evidence explaining how temperature affects the arrangement and motion of the particles in a substance.
Ask students to take some time to silently read the skill, underline the important vocabulary, and rank their level of mastery on a scale of 1 to 4 (4 being mastery) next to the skill. Self-assessment is so important to growth. Take the time to have students reflect on where their learning is at on this first day of learning about this skill.
Explain that in the lab rotation for today, students are going to investigate how adding and removing heat energy can affect the arrangement and motion of the particles in a substance including the state of mater, mass, volume, and density.
Students need practice, direction, and instruction in how to participate in group discourse. One strategy that I have found very helpful is using a “Fishbowl”.
Description of Fishbowl Activity: Have a group engage in a group conversation at a table in your classroom with the remainder of the class surrounding that table. The group discussing are like fish in a fishbowl with the class looking in. Then, have the "audience" share what strategies they saw that were effective in the group's discourse. Be careful here! Students will struggle with how to provide criticism appropriately. I like to use "3 stars and a wish" in which students giving feedback provide 3 successful strategies they notice and 1 wish they have. Providing them with the sentence starter, "I wish..." helps students communicate the areas for improvement more professionally. Two key elements that I find are helpful to add to this strategy are:
In promoting group discourse I find it very important to be explicit in your expectations. Let students know what you expect and provide them with sentence starters that might help them achieve discourse. Here are some I use with my students:
There are so many more! I add to my list every year!
Start With a Demonstration:
Place a balloon full of pop in a microwave and allow the students to watch as you heat it for a couple minutes (A marshmallow works too :). Ask students to make observations and look for evidence of how adding thermal energy affects the physical properties of substances and how the particles are arranged. The balloon should expand and eventually pop!
Fishbowl: Provide Students With Roles
Next explain to the students that you are going to go through a Fishbowl Activity to discuss what was just witnessed. Choose a group of students and sit down at a table with the class surrounding the table.
*Prior to doing this, provide the students with a slip of paper that says their role during the fishbowl. Students may participate as they feel is correct in a group conversation; however, they must at some point exhibit the behavior that they have on their slip of paper. Here are some of the roles I might give are:
Sometimes I even give students more than one slip of paper. The key is that the students understand that they are to actually act as if they believe is appropriate group discourse at all times in the conversation. The only exception is completing the task provided on their slip, which only needs to be done once. The remainder of the time, they should just act as if they are demonstrating excellent group discourse. (Other than the student that is not supposed to speak unless spoken too.)
Fishbowl Discussion Questions:
With you acting as a group member as well, engage in conversation with the group in the fishbowl and let the discussion questions lead you as a guide. Let the conversation develop. Provide no feedback as the conversation is taking place. Your interactions are key. Make sure that you interject with comments that are important for the group to hear (even if they are wrong).
Fishbowl: Group Feedback on Discourse
Following the discussion, ask the students outside the fishbowl to provide feedback on the discussion in the format of “Three Stars and a Wish” (We go through multiple rounds of this). Students offer three positive group discourse actions they saw and one wish they would like to see improved. Explain to the group that it is important to provide feedback in a respectful way and not to judge those in the group. Emphasize that each group member was given a role of how to act so they may have been making mistakes on purpose! (This takes pressure off the fishbowl participants.)
The following video is one of my classes' fishbowl conversation. In the video, I added callouts/speech bubbles that indicate the behaviors that students noted in the "Three Stars and a Wish" reflection discussion. In addition, I add callouts indicating some examples of students acting out their provided roles.
Provide the students with the Density Lab Rotation Student Document. Go through the procedures and safety precautions for each station. Let students know that today they will be practicing sound group discourse. They will not be writing the answers, but discussing them instead! Students will be expected to use the strategies discussed in the fishbowl as they verbally answer the questions in the lab. Explain to the students that the only thing they have to write down is any measurement they take. So, anytime they are asked to measure mass, volume, or density, they must write the numbers down in the appropriate places on their lab sheet. However, if it is a question, students will use their best group discourse strategies to discuss the lab stations.
As a teacher, it will be critical that you check in with every group as much as possible to listen in on their conversations and provide them with feedback. Also, it will be important for you to ask questions to those learners that tend to be quiet in group settings. Ask them questions that they can respond to confidently!
After students have completed the entire rotation, meet as a whole class and discuss each lab station as a large group. This is so important to clarify any misconceptions that group's had at the stations. I like to call on students randomly during this discussion to encourage accountability in participation.
The upcoming sections go into detail about procedures, teacher tips, and the key discussion points. In addition, I have included a few resources here. Other than the student lab document, I have also included your answer key and a Density Reference Sheet students can use to reference textual evidence as they discuss.
Will It Sink Or Float?
Have the water you put the cans in be warm! It will help with the Coke sinking!
Let students know the volume of the pop is on the can! They should not open the pop cans.
Key Discussion Points:
Students recognize that the cans have the same volume, but different masses. They determine that the larger the mass, the larger the density. Also, they discover that it is the sugar in the Coke that makes it more dense.
Is Salt Water Denser Than Pure Water?
For the "Plastic", I use a plastic paper clip I have although I have used the top part of a plastic spoon before. The key is that it has to be the right density to sink in pure water and float in saturated salt water.
Key Discussion Points:
Students realize that the salt water is more dense than the fresh water because adding salt adds more molecules and mass to the same volume. Students also discuss what makes an object sink or float.
Making a Cartesian Diver:
Make these ahead of time! You must use glass eyedroppers.
At some point, the diver will "stop working". This just means that water has gotten stuck in the eyedropper. Simply empty the water until you can get out the eye dropper, squirt the water out and refill. It will be fixed!
Key Discussion Points:
Students recognize that when the bottle is squeezed, the eye dropper fills up with water. They should realize that the volume of the system (the eyedropper itself) does not change, but that the mass increases. Thus, they discover that the eyedropper becomes more dense because there are more molecules packed in the same space and it becomes more dense causing it to sink.
Densities of Solids and Liquids:
Part 1: Rectangular Prisms
Part 2: Irregularly Shaped Solids
Pick your own set of random materials. One set of rectangular prisms and one set of irregularly shaped objects.
If using things like staple boxes or tape roll boxes, emphasize to students that they are to use a ruler to calculate the volume and they are not to place the cardboard boxes in water!
Key Discussion Points:
Students get more practice at using displacement and calculating density. In addition, they practice calculating volume of a rectangular prism by multiplying the length by the width by the height. They should also focus on using appropriate units in their measurements.
Determine the Density of Water:
Repeat the procedure using a different volume of water. The amount is your choice!
Key Discussion Points:
Students realize that water has a density of about 1.0 g/ml. They also recognize that tap water is not pure water and that other things are dissolved in it resulting in a density that is not exactly 1.0 g/ml. Also, they begin to develop their understanding of the idea that density is proportional as they calculate the density of water with two different volumes and realize the density is still the same. (Students have a hard time with this. Many think that if you have half of the water, you will have half of the density.)
Ball and Ring Apparatus:
Goggles at all times at this station!
Emphasize the appropriate height for a Bunsen burner flame.
Emphasize to only grab the ball and ring by the handles. If a student comes to a station, they need to understand that it could still be hot from the previous group.
You can purchase this right from Amazon.
Key Discussion Points:
In this lab, students see that when thermal energy is added, the molecules spread apart resulting in an increase in volume and a decrease in density. In addition, they see that the reverse is true when thermal energy is removed. Last, students develop the idea that when thermal energy is added, that the mass does not increase. In the video below, you will see the typical reaction when students are asked if adding heat increases the mass. They tend to pause and really think before answering! When this video ended, I did provide them with some feedback. First, the height of their flame is too high. Safety first! Next, after answering that the mass of the ball stayed the same, they should have followed it up with their reasoning. With density and volume they referenced the molecules spreading apart, with mass they might reference their Density Reference Sheet and note that mass is how much matter is in an object and by adding heat we are adding energy not matter.
On the board or chart paper, inside of a light bulb with light rays coming out of it, write the question "What are your go to group discussion phrases?"
Ask students to add their phrases to the light bulb graphic organizer. Keep the light bulb posted in the classroom so that students can not only reference them but add to the graphic organizer as they come up with more phrases worth sharing. The picture below is an example of this light bulb graphic organizer.