Once You Pop, You Can't Stop! Lab Rotation

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Objective

Students will be able to analyze and interpret data on the properties of substances to determine if a chemical reaction has occurred and recognize the total number of atoms does not change in a chemical reaction and thus mass is conserved.

Big Idea

The lab stations that focus on chemical reactions and conservation include using a battery to light steel wool on fire, forming a green precipitate by mixing two clear solutions, "magically" lighting the end of a skewer on fire, and more!

Introduction and Connection to the NGSS and Common Core

In this lesson, students use text strategies as they obtain information about the Law of Conservation of Mass.  Then, students go through a series of lab stations in which they have to determine evidence of chemical reactions and the conservation of matter.  The lab stations are very engaging for middle school students and include using a battery to light steel wool on fire, making popping sounds with a mix of zinc and HCl, forming a green precipitate by mixing two clear solutions, "magically" lighting the end of a skewer by placing it in a flammable bubble and popping a zip lock bag of vinegar and baking soda!

This lesson is designed to connect to the following NGSS and Common Core Standards:

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-PS1-5  Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved. 

CCSS.ELA-LITERACY.RST.6-8.1  Cite specific textual evidence to support analysis of science and technical texts.

CCSS.ELA-LITERACY.RST.6-8.3  Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.

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.WHST.6-8.9  Draw evidence from informational texts to support analysis, reflection, and research.

Science and Engineering Practices:

When using the text strategies utilized in this lesson, students think deeply about text in order to make their own conclusions and consider solutions to problems.  Thus, students are using the scientific principle of Generating Questions and Designing Solutions which states that, "Students at any grade level should be able to ask questions of each other about the texts they read, the features of the phenomena they observe, and the conclusions they draw from their models or scientific investigations." (SP1)   In addition, when utilizing text, students use strategies to obtain scientific information and evidence from text (SP8).  

Crosscutting Concepts:

As students are introduced to the Law of Conservation of Mass, they build understanding that matter is conserved because atoms are conserved in physical and chemical processes. (Energy and Matter)

At each lab station, students use patterns in evidence to identify each reaction as chemical or physical.  Students thus realize that patterns can be used to predict phenomena. (Patterns)

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

5 minutes

Ask students, "What are you going to learn today?".  Students should respond by saying that they will be answering the Essential Question, "How do particles combine into new substances? And, what evidence can show how the physical and chemical properties of the substances change?"  This EQ is posted on my board and on the student's Chemistry Unit Plan

Explain to students that this lesson represents the first lesson that students work with Skill 6 of the Chemistry Unit Plan, "I can explain that when a reaction occurs that energy can be gained or released, but the amount of matter in the system stays the same."  Have the students turn to their unit plans and silently read the skill.  After reading the skill have the students rank their current level of mastery on a scale of 1 to 4 (4 being mastery).  Remind them that as this is their first encounter with this skill, it is perfectly fine to be at a 1 or 2.  This is just the starting point!  We will grow from here.

In my classroom, students frequently self-assess their level of understanding on each skill in the unit as we go.  As you can see from the image below, this student ranks himself as a "3" to start this lesson.  As we work more on this skill in the upcoming lessons, the student re-assessed and updated this score.

*Students in my class have already gone through several lessons about chemical reactions and properties.  I have included these notes pages in the resource section so you can have an idea of where we have been prior to this lesson!

For a look at all the lessons that have led my students to this point and where we go from here check out the lessons in these units:

Physical Properties:  Molecular Arrangement and Phase Changes:  Focuses on Skills 1 - 4 of the Chemistry Unit Plan

This unit is designed to answer the Essential Question, "How do particles combine into new substances? What evidence can show how the physical and chemical properties of the substances change?"  It particularly focuses on types of matter, physical properties, phase changes, and factors that affect physical properties. This unit's purpose is so much more than just the content, however. It's focus is scientific literacy. It stresses group discussion, discourse and utilizing text references when engaging in argument. Students utilize reading, writing, and speaking strategies in order to develop scientific literacy. It's scientific literacy immersion!

Chemical Properties and Reactions:  Focuses on Skills 4 - 6 of the Chemistry Unit Plan.

This unit is also designed to answer the Essential Question, "How do particles combine into new substances?  What evidence can show how the physical and chemical properties of the substances change?"  This unit focuses on chemical properties and chemical reactions.  Students analyze evidence and property changes that allow them to distinguish between chemical and physical reactions.  In addition, students investigate the Law of Conservation of Mass as they look at how bonds are broken and formed in chemical reactions.  This unit is full of hands on labs and station rotations that will engage any middle school student in chemistry!

Mini Lesson: Conservation of Mass

25 minutes

To introduce the conservation of mass, I have the students "talk to the text" and climb the "Ladder of Discourse".  Talking to the text is a way students document their thinking as they read.  When they read they try to climb the "Ladder of Discourse".  Each "rung" in the ladder increases in complexity in student thinking.  Check out the Ladder of Discourse Description of Rungs for more details.

The highest levels on the "Ladder of Discourse" are "Found it!" and "Discourse".  "Found it!" represents students making scientific connections or answers to scientific questions.  "Discourse" occurs in students connecting to the Crosscutting Concepts that the NGSS has identified.  Students use the Crosscutting Concepts to develop scientific questions or connections that go beyond the text.  The student above is attempting to connect to Structure and Function as they ask, "Does the structure of the molecule affect how much energy is released? Double bonds?".  In addition, they connect to the idea of "Scale, Proportion, and Quantity" when they ask, "Is the energy of a reaction in proportional?  If the products are doubled is the energy doubled?".

The labs that follow will provide the students with more experience with these concepts.  One concept I like to review before proceeding, however, is the reaction at the top of the second page of the notes page.  On the students copy, the molecules will not be in color. I have found it helpful to project the color picture of the molecules in the reaction and have the students discuss the following questions as a class:

  • What color atoms do you notice on the reactant side of the equation? (Red, Black and White)
  • What color atoms do you notice on the product side of the equation?  (Red, Black and White)
  • (Note that they are the same colors in the reactants and products) 
  • What do the different color "spheres" represent? (atoms/elements)
  • For each of the following questions, I physically touch each atom with a meter stick and count them to make it very visual for the students.
  • How many red atoms are there on the reactant side? (4)
  • How many red atoms are there on the product side? (4)
  • How many black atoms are there on the reactant side? (1)
  • How many black atoms are there on the product side?  (1)
  • How many white atoms are there on the reactant side? (4)
  • How many white atoms are there on the product side? (4)

(Note all are the same on each side of the equation and state the Law of Conservation of Mass.)

Then, I look at the written version of the reaction.  Discuss the meaning of coefficient and subscript.  Talk through the same questions listed above but replace the colors with the atom names (red=oxygen, black=carbon, white=hydrogen).  Students will begin to see patterns and some will determine that you can multiply the coefficient by the subscript to determine the number of atoms.  While this is great, I make sure that I connect this idea to the picture above.  So, if a student says there are 4 oxygen's because they multiplied 2 x 2, I use a meter stick to count on the picture above the 4 oxygen atoms.  It helps students visualize that a coefficient represents the number of molecules when I can visually point to the two molecules above.  And, in the same sense, it helps them see that the subscript is the number of atoms of that element in one molecule when I point to the two oxygen atoms in each of the oxygen molecules.

Following this discussion, I provide the students with the Once You Pop, You Can't Stop Lab.  I emphasize a few things before beginning:

  1. Wear goggles!  
  2. Read all procedures carefully!  
  3. Reference the text (the notes page) on any question that you need help with.

More detailed descriptions of each lab station are included in the following sections along with procedures, pictures of lab set ups, teacher tips, videos and pictures of the reactions, and student work.

Station 1: Once You Pop, You Can't Stop Lab

15 minutes

The Set Up:

Procedure:

  1. Put on goggles.  The student handling the test tube should wear gloves.
  2. Pour 1 eye dropper full of HCl into a test tube.
  3. Add some zinc to the test tube.
  4. Wearing gloves, stick your thumb into the test tube to create a plug. 
  5. You should keep your thumb in the test tube until you feel pressure under your thumb as the gas builds up.
  6. Another student should light a match when the gas has built up. (Don’t complete step 7 until the match is lit!)
  7. Remove thumb and pass a lighted match over the top of the test tube!  Listen closely!

 Teacher Tips:

  • Safety is essential here!  Goggles and vinyl gloves!
  • I use 1.0 M HCl and zinc pellets.
  • Give your students a talk about gloves.  There is something about vinyl gloves and middle school students.  They will waste them or blow them up like balloons if you do not address it before beginning the lab.
  • It is important that the match is ready to go and passes over the test tube quickly or too much gas will escape and you won't get the sound you are looking for.

The Reaction:

A Look at Student Work:

 

The first two questions ask the students to recognize that in a chemical equation the reactants are to the left of the arrow and the products are on the right of the arrow.  In the second question, the student identifies gas production, pH change and temperature change as evidence that this was a chemical reaction.  For each of those pieces of evidence, she also includes observations from the lab that supported her claim.  For example, she does not simply say "gas production".  She states that she observed "gas production because bubbles formed".  Notable vocabulary in this student's response is use of the word "exothermic".  This is an application of a vocabulary term in the notes the student read at the beginning of the lesson.  All of my students do not do this, and it is exciting when it happens!  For the last question, many students will choose "a".  Students struggle distinguishing between a "chemical property" and a "sign of a chemical change".

Station 2: Start the Fire, Wool Ya?

10 minutes

The Set Up:

The Procedure:

  1. Put on goggles.
  2. Using the tongs, grab a piece of steel wool and place it on the 6 volt battery so that the steel wool is touching both prongs.
  3. Watch and observe the chemical changes that take place.  Do not touch the used wool; it is hot!

 Teacher Tips:

  •  Safety!  Goggles and an emphasis on not touching the used wool is key.
  • I would give each group a small piece of steel wool that they can break apart and share.  This reaction is so cool that they will overuse your materials if you do not portion it out.

The Reaction:

A Look at Student Work:

 

The first two questions ask the students to recognize that in a chemical equation the reactants are to the left of the arrow and the products are on the right of the arrow.  In the second question, the student identifies gas production, color change and temperature change as evidence that this was a chemical reaction.  For each of those pieces of evidence, she also included observations from the lab that supported her claim.  For example, she did not simply say "color change".  She stated that she observed "color change because the steel wool changed from grey to blue".  In the last question, the student recognizes that if the mass of the reactants used was 15 grams, that the mass of the products would also be 15 grams.

Station 3: Steel Wool and Vinegar

10 minutes

The Set Up:

The Procedure:

  1. Put on goggles.
  2. Fill a test tube with 3 large eye droppers full with iron acetate.
  3. Add an eye dropper of ammonia.  Continue to add ammonia until you see the precipitate form!

Teacher Tips:

  • To make iron acetate, simply put steel wool in a jar and cover it with vinegar.  Place it in a dark cupboard for a few days.  Iron acetate is the liquid that forms.
  • This can be messy.  As you can tell from the test tube below, you will want a test tube brush and place to dump the test tube.
  • Even though it is obvious to an adult that green chunks are forming, some middle school students do not recognize that the green is from green, solid particles inside.  For some middle school students, when they are picturing "solid formation" as a sign of a chemical change, they are looking for something "hard".  I frequently check in with the students at this station to make sure they are noticing the precipitate.
  • If you let a test tube sit for a little while, the solid particles settle and it can become more clear.

 The Reaction:

A Look at Student Work:


The first two questions asks the students to recognize that in a chemical equation the reactants are to the left of the arrow and the products are on the right of the arrow.  In the second question, the student identifies precipitate formation, color change and pH change as evidence that this was a chemical reaction.  For each of those pieces of evidence, she also includes observations from the lab that supports her claim.  For example, she did not simply say "pH change".  She states that she observed "pH change because vinegar is an acid and ammonia is a base".  In the last question, the student recognizes that the number of atoms before and after the reaction is the same.

Station 4: Bubble Bang

10 minutes

The Set Up:

The Procedure:

  1. Put on goggles.
  2. Fill a sandwich bag about a quarter of the way full of vinegar.
  3. Add a few drops of red cabbage juice to turn the vinegar pink.
  4. Close the sandwich bag almost all the way closed, leaving just enough room to scoop in the baking soda.
  5. Add a tablespoon of baking soda to the bag and close it quickly!  Hold the bag over the sink!
  6. Release the packet of baking soda and observe!

Teacher Tips:

  • I use cabbage juice that is left over from my previous pH labs.  If you have not completed any pH labs with cabbage juice prior to this, you will have to make your own.  Bring a large pot 3/4 full of water to boil.  Add as many leaves of cabbage as you can and allow to cook for about an hour.  Then, remove the leaves of cabbage and cool the liquid.  Keep refrigerated.  
  • As noted in the procedure, it would be beneficial to hold the bag over the sink as it will often pop!
  • Make sure the students touch the bag, it gets very cold!

The Reaction:

A Look at Student Work:


The first two questions ask the students to recognize that in a chemical equation the reactants are to the left of the arrow and the products are on the right of the arrow.  In the second question, the student identifies gas production, color change, temperature change, and pH change as evidence that this was a chemical reaction.  For each of those pieces of evidence, she also includes observations from the lab that supports her claim.  For example, she did not simply say "temperature change".  She states that she observed "temperature change because it got colder".  In the last question, the student recognizes that the elements in the reactants are the same as the elements in the products.

Station 5: X Men Mania Fire Thrower

10 minutes

The Set Up:

The Procedure:

  1. Put on goggles.
  2. Measure about 30 ml of hydrogen peroxide and pour it into a SMALL beaker.
  3. Add ½ teaspoon of dry, active yeast and stir well.  Bubbles will begin to rise to the top of the beaker.
  4. Once the bubbles have reached the top of the beaker, look to see if there are any tan yeast particles in the bubbles.  If there are, gently swipe your finger across the top of the beaker to remove the bubbles with yeast. 
  5. Now you should see pure white bubbles in the beaker.
  6. Take a skewer and break it in half.  Light the end of the skewer and let it burn for about 30 seconds.
  7. Blow out the flame so that there are red hot embers remaining.
  8. Take the hot end of the skewer and hold it completely vertical.  SLOWLY lower the skewer into the WHITE bubbles.  As soon as the skewer lights on fire, remove it.  Blow out the flame and try again!

Teacher Tips:

  • Practice this one before you have the kids do it.  It is important for you to be able to give the students tips on how to be successful.
  • When mixing the yeast in the hydrogen peroxide, swirl it really quickly and vigorously.  Then, STOP!  If you swirl for too long, it doesn't work as well.
  • Dry active yeast can be used year after year.  I refrigerate mine after I have opened a jar.
  • It is important that the skewer has red embers on it before lowering it into the bubbles.
  • Lower the skewer straight down, not at an angle.
  • If you lower the stick to quickly, it will become wet from all of the bubbles and will not work.  It is very important to go slow and to remove the skewer once it ignites.
  • Once the skewer ignites, have the students pull it out, blow it out, and let another student try.  The reaction is so cool, but if the first student doesn't pull out the skewer, they can "use" up all of the oxygen bubbles and no one else will get a chance.
  • In my class, this is actually the second time we have used this lab station (Pop Your Top is the other lesson); however, the questions here are geared towards conservation as opposed to evidence of a chemical change.

The Reaction:

A Look at Student Work:

 

In this set of questions, the students have to identify the reactants and products of a reaction based on a chemical equation.  Then, they have to count the number of atoms of Hydrogen and Oxygen on each side of the equation.  This student correctly identifies that there are 4 atoms of each on both sides of the equation.  Students have a hard time correctly stating that there are 4 atoms of oxygen in the products as there are oxygen atoms in both molecules.  Many students need help with this.  This student also notes that this reaction is exothermic because her hands, the surroundings, felt warmer.  This means energy was being released.  In the last question, the student notes that a reaction is exothermic if the amount of energy released when the bods are formed is greater than the amount of energy needed to break the bonds.

Station 6: Marshmallow Molecules

10 minutes

The Set Up:

The Procedure:

  1. Set one CH4 molecule in the first reactant spot.
  2. Set 2 O2 molecules in the second reactant spot.
  3. The arrow means “yields”.  It means that a chemical reaction is taking place.
  4. To show that a chemical reaction is taking place, break the toothpicks that connect the marshmallows of the reactants together.
  5. Rearrange the atoms and reconnect them in order to form the products.  REMEMBER:  There is a specific way that we make carbon dioxide and water molecules.  Make sure to build them correctly.
  6. Place the CO2 in the first product place and set the 2 water molecules in the 2nd products place.

Teacher Tips:

  • Before students can rotate from this station, I ask that they show me their products.  It is important that students not only problem solve and correctly create carbon dioxide and water, but for me it is important that they create these structures accurately.  In previous lessons, students learned that water is in a triangular shape and that carbon dioxide is double bonded.
  • I create laminated cards for this station; however, you could simply use note cards.
  • Include a key at the station identifying which color marshmallow represents each element in the reaction.
  • You will need to create the reactant molecules with marshmallows and toothpicks prior to the lab.  You will need twice the amount of oxygen molecules than methane.

A Look at Student Work:


In the questions for this station, students are asked to consider many important topics in terms of conservation.  Students note that the number of atoms (marshmallows) are the same before an after the reaction. Students answer that while the elements are the same before and after the reaction, the molecules are different.  They note that bonds are broken and formed and that there is an energy shift when this occurs.  Last, they take time to recognize that water and carbon dioxide have a specific structure.

Station 7: Insta-Snow Lab

10 minutes

The Procedure: (Students completed 1 - 9 in a previous lab 2 weeks ago.  Students only complete step 10 in this lesson.)

  1.  Label a small beaker with the names of the members in your group.
  2. Add one small scoop of sodium polyacrylate to a beaker and measure the mass.
  3. Measure the mass of the beaker with the sodium polyacrylate and record the mass in the data table.
  4. Place an different empty graduated cylinder on the scale.  Press the “Zero” button.  The scale should read 0.0 grams.
  5. Add 10 milliliters of water to the graduated cylinder.
  6. Record the mass of the water in the data table.
  7. Pour the water in the beaker of sodium polyacrylate.
  8. Measure the new mass of the sodium polyacrylate beaker.
  9. Place in the window sill. 
  10.   After 1 or 2 weeks, measure the mass of the beaker again.

Initial Set Up With Water Added:

After Weeks/Post Evaporation:

A Look at Student Work:

In this lab, students first have to analyze the data to determine that the total mass of mixture is simply the mass of the sodium polyacrylate and water added together.  In the next question, the students note that the mass decreases from 19.1 g to 9.5 g because the water evaporated.  It is important that students compare two data points here rather than just saying, "The mass decreased."  Last, the students explain that mass is conserved as the original mass is the same as the mass after the reaction.  I would have loved this student to have backed up her answer with data, specifically stating that the mass was 9.5 g to start and 9.5 g to finish.  Including data when data is available is something that middle school students typically need work on.

Closure

5 minutes

To close the lesson, have a whole group discussion about each lab station.  Typically, I do not go over all of the reactant/product questions for each station as those are repetitive.  I simply discuss those for the first station.  The focus of this discussion is on identifying evidence of a chemical change and backing up their evidence with qualitative observations from the lab and in answering the conservation questions for each station.  

Just before the end of the class period, I ask a series of questions that have repetitive answers. This helps drive home the main idea of the lesson.  These questions include:

  • Butane is placed in a sealed zip lock bag.  The bag is placed on a scale and the mass is measured. It begins to boil.  Eventually all of the liquid evaporates.  The bag is again placed on the scale to measure the mass.  How would you compare the mass of the bag after evaporation to the bag when it was a liquid? (The same!)
  • The reactants in a reaction have a mass of 100 kg.  How would you describe the mass of the products? (The same!)
  • The elements in the reactants are hydrogen and oxygen.  How would you describe the elements found in the products? (The same!)
  • Just to make sure they are paying attention....How would you describe the molecules in the reactants to the molecules in the products? (Different!)
  • Water is placed in a ice cube tray and placed in a freezer.  How would you describe the mass of the ice cube tray after freezing compared to when the liquid water was in it? (The same!)
  • In the X Men Mania lab, hydrogen peroxide decomposed.  How would you describe the total number of atoms in the reactants compared to the number of atoms in the products? (The same!)