Density Lab Stations

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Objective

Students will be able to explain how the state of matter and temperature of a substance affects the physical properties of that substance.

Big Idea

Students go through a series of lab stations in an exploration of density. They use Cartesian Divers, Coke and Diet Coke, and a Bunsen Burner Ball and Ring Apparatus help make students engaged in group discourse about density!

Introduction and Connection to the NGSS and Common Core

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).

Crosscutting Concepts:

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.

Connecting to the Essential Question: What are you going to learn today?

5 minutes

 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.

Background and Explanation of the Fishbowl as a Strategy for Group Discourse

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:

  1. You should be in the fishbowl! You have the knowledge of effective and ineffective discourse.  You should "act" out both effective and ineffective strategies as you engage with the group.  The more authentic you are in the way you speak and act (sound like your students!), the more effective you will be! 
  2. Prep the students that are in the group.  Give them roles.  For example, you could tell a student that they are to "play" with all the materials at the lab station while the group discusses.  You could tell another to make sure that they touch the text when they cite evidence from it.  Whatever the key qualities you are focusing on, ask students to show them.  This strategy can be pulled out of your hat at any time!  If you see your students having a need in an area, have them fishbowl it!

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:

  • Everyone participates. Have an awareness of your group members.  Not everyone will feel comfortable in speaking.  If you notice a member that hasn't spoken, ask them their opinion.  If you notice a member that is shy or in the process of building confidence, ask them questions they can give immediate feedback to and let them know what you liked about what they said.  For example, you might say, "I like how you....." and follow it with "I would love to hear more of your ideas."
  • Ask follow up questions.  Even if you agree with a classmate's opinion, if they haven't provided evidence say, "That's an interesting idea.  What evidence lead you to that opinion?"
  • Point to the text when you are referencing textual evidence.  If a group member shares an idea and says it came from the text, say "I'd like to read more.  Can you show me where the text says that?".
  • Leave your ideas open to feedback and suggestions.  When offering ideas, let your group members know that you want their feedback.  You might start by saying, "Correct me if I'm wrong....".
  • Always back up your ideas with evidence.  When providing an opinion, you might state your idea and then say "The evidence that supports this idea can be found in the....(data, text, etc.)"
  • Use science vocabulary!  When speaking, sound like a scientist!  Keep text and notes handy so that as you speak, you can look up words if you need to!  If a student in your group is not using science vocabulary, you might say, "What do you mean by ________?  Is there another word for that?"
  • Don't be afraid of not knowing. At some point you are going to feel as if you are not quite sure what the answer is.  You might be confused. You might not understand.  This does not mean that you can't be an effective group member.  Asking questions can promote group discourse.  Ask questions like, "Do we have any data that can help us?", "What does the text say about this concept?", or "What evidence have you seen in your life that relates to this topic?".
  • Disagree based on evidence.  Instead of saying, "You're wrong." or "I don't agree.", say something that shows you have evidence to the contrary and you are looking for your own feedback.  That will allow your group member to not get defensive.  You might say, "I notice in the text it says _________________.  How will that affect what you are proposing?", "The data states ____________________.  Does this support what you are saying?", or "What qualitative observations did you make that showed you this?".

There are so many more!  I add to my list every year!

Mini Lesson: Fishbowl

25 minutes

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:

  1. At some point in the discussion, get out your Density Reference Sheet, point to a place in the text that provides evidence, and read it to the group.
  2. At some point in the conversation, talk to someone else about something you saw on twitter or your favorite (appropriate) app when a member of your group is talking.
  3. At some point in the discussion, ask the question, “Is there any evidence in the text that can support this?”
  4. At some point in the discussion, make a point about the molecules and physical properties but use words like “it and they” repeatedly instead of using science vocabulary.
  5. At some point in the discussion, say to another group member that just offered an idea.  “That was a horrible idea.  I think you're wrong.”
  6. Don't say anything at all in the conversation unless someone directly asks you your opinion.
  7. Pay attention to who has spoken and who has not.  Say to a person that hasn't spoken, “You usually have really good ideas.  Did you see any evidence you could share?”

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:

  • What physical properties changed when heat was added?  What evidence do you have to support that?
  • How did adding thermal energy affect the motion and arrangement of the molecules?  What evidence do you have to support that?
  • Did the volume of the ball increase? What evidence do you have to support that?
  • Did the density of the balloon increase?  What evidence do you have to support that?

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.

 

Density Lab Rotation

45 minutes

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.

Stations 1 and 2 Descriptions: Will it Sink or Float and Is Salt Water More or Less Dense than Fresh Water?

Will It Sink Or Float?

  1. Place the Coke can in the aquarium filled with water. Did the Coke sink or float?
  2. Place the Diet Coke can into the same aquarium filled with water.  Did the Diet Coke sink or float?
  3. Measure the mass of the Coke and Diet Coke cans on the scale.  Record your measurements in the data table below.  HINT:  For the volume, look on the can itself!

Teacher Tips:

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?

  1. Place the plastic in the beaker of plain water.  Observe if it sinks or floats. 
  2. Stir the salt water.  Place the egg in the beaker of salt water.  Observe if it sinks or floats.

Teacher Tips:  

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.

Stations 3 and 4 Descriptions: Making a Cartesian Diver and Densities of Solids

Making a Cartesian Diver:

  1. Fill a 2-L bottle nearly to the top with water.
  2. Drop in the glass eyedropper.
  3. Tightly put the cap back on the bottle.
  4. Squeeze the sides of the bottle until the eyedropper sinks to the bottom.
  5. Try to keep the eyedropper suspended in the middle of the bottle by applying different amounts of pressure on the bottle with your hands.

Teacher Tips:

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

  1. Choose an object to measure.
  2. Place the object on the scale.  Record the mass.
  3. Using a ruler, measure the length, width, and height of the object.  Record the volume.
  4. Calculate the density.

 Part 2:  Irregularly Shaped Solids

  1. Using the scale, weigh the object you have chosen and record the mass.
  2. Fill the beaker of water with water.  The amount is your choice.  Record this data.  Remember to measure from the meniscus!
  3. Place the object into the beaker of water. Record the new volume of the liquid.  Remember to measure from the meniscus!
  4. Subtract the new volume from the previous volume to find the displacement. (New Volume)  -  (Old Volume) = Volume of object

 Teacher Tips:

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.

Stations 5 and 6 Descriptions: Density of Water and Ball and Ring Apparatus

Determine the Density of Water:

Part 1

  1. Measure the mass of an empty beaker.  Record this data.
  2. Pour in an amount of water. (YOUR CHOICE).  This is the volume.  Record this data.  Remember to measure from the meniscus!
  3. Place the beaker with the water on the scale and measure its mass.  Record this data. 
  4. Subtract the mass of the empty beaker from the mass of the beaker with water.  This is the mass of the water.  Record this data.
  5. Calculate the density.

 Part 2:

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:


  1. Take the ball and ring and push the ball through the ring to see if it can pass through.
  2. Heat the ball over a Bunsen burner for 2 minutes. 
  3. Try again to push the ball through the ring.
  4. Put the ball immediately in the bucket of ice water for 1 minute.
  5. Try again to push the ball through the ring.

Teacher Tips:

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.

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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.

Closure: What are your go-to group discourse phrases?

5 minutes

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.