Chocolate Changes State

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Objective

SWBAT draw a model and label what is occurring as chocolate changes state.

Big Idea

Students will be making their own yummy treats by melting chocolate, adding it to candy molds, and then freezing it back into a solid.

Rationale and Preparation

The Why Behind Teaching This: 

Unit 2 addresses standards related to matter and it's interactions.  The unit begins with identifying types of matter and the particles that make it up.  This is covered in standard 5-PS1-1: Developing a model to describe that matter is made of particles too small to be seen.  We will be changing matter by melting, evaporating, and dissolving to prove that although the physical appearance has changed, the same amount of matter  still exists.  This is covered in standard 5-PS1-2: Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.  We will also be using a variety of properties to identify matter through standard 5-PS1-3: Make observations and measurements to identify materials based on their properties.  The investigations and experiments during this unit will focus on physical and chemical changes that occur when mixing matter which addressed in standard 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in a new substance.

This specific lesson addresses standard 5-PS1-1: Developing a model to describe that matter is made of particles too small to be seen.  Students model what happens to the particles that are too small to be seen through a the creation of a comic strip about those particles.  It also addresses standard 5-PS1-3: Make observations and measurements to identify materials based on their properties.  As we describe the chocolate at each state using physical properties.      

Lesson Goal: 

The goal of this lesson is for students to demonstrate an understanding of how the particles are arranged differently, and move differently, as heat is added or taken away, causing matter to change state.  

Success Criteria:

Students will demonstrate their understanding by creating a comic strip that is evidence of their understanding that the particles spread apart and move faster as heat is added, and they come back together and move slower as heat is taken away.   

Preparing for Lesson:

Warm Up:

  • A piece of dry ice and metal such as a a metal leg on a chair to demonstrate the sound produced by dry ice as it changes to a gas.   

Guided Practice: 

  • Anchor Chart sectioned off into 2 comic strips to model how to create a comic strips for particles changing. 

Explore: 

  • A copy of the comic strip template for each student 
  • Enough Candy Melts for each group to have a bag full.  I use a different color of chocolate for each group. 
  • Icing Bag for each group (these are what the chocolate goes in as they do not melt in the microwave like other bags would). 
  • Microwave for melting the chocolate 
  • Candy mold for each group 
  • Candy sticks, craft sticks, or pretzels to stick in the mold when complete 
  • A refrigerator for freezing the chocolate back into a solid    

Wrap Up: 

Warm Up

10 minutes

Activating Prior Knowledge: 

I review the two previous lessons on states of matter with students by asking them to describe the particles in each state.  I ask them to describe what happens to a solid when we add heat.  They tell me it melts, and I ask them to explain what is happening to the particles that causes it to melt.  They say the particles speed up and spread apart.  We go over evaporating, condensing, and freezing as well.  

I ask students if they think items can go directly from a solid to a gas and skip the liquid step.  The majority of students don't believe they can, a few say yes.  I get a piece of dry ice out of a cooler (using a piece of cloth to hold it) and ask them what state of matter I am holding.  They tell me it is a solid.  I then have students give me some properties of the substance that help them identify it as a solid.  I am checking for understanding of the concept that solids do not change shape.  I then ask students to describe the particles that make up the ice, how are they configured and how are they moving.  They tell me that the particles are tightly packed and vibrating. 

Building Excitement: 

I tell students that they can actually hear the particles in this solid vibrate and I hold the piece of dry ice against a chair leg (that is metal) and we all hear it make a loud screeching sound. The students are shocked to hear the noise.   I lead a conversation about dry ice being a frozen gas and that it is one substance that can change directly from a solid to a gas.  Because these particles are moving so quickly trying to change into a gas, they actually vibrate fast enough to produce that sound.  This activity is simply to review concepts already taught and build excitement in students.  It leads us into our lesson for the day on matter changing state because I use this to model my expectations for the comic strip that students will create throughout today's lesson.  

This Video of dry ice demonstration shows the section of the review where I am actually holding the dry ice against the metal so the students can hear it.  You can hear the shock and excitement in their reactions as they hear the screeching sound made by the particles in the dry ice.  

For additional activities you can do with the left over dry ice you will have, check out other dry ice experiments.

Guided Practice

10 minutes

Modeling Comic Strip Writing:

I display a large sheet of chart paper on the front board.  After our discussion about dry ice changing directly from a solid to a gas, I explain to students that they will be writing a comic strip today to demonstrate their understanding of how particles are arranged in matter.  I ask students to describe to me how they would feel if they were a particle making up that dry ice.  I get answers such as cold, and screaming against the metal.  

I explain that neither of these descriptions would reflect an understanding of how particles are arranged.  I need them to describe how they would feel in a way that demonstrates their understanding of how the particles are arranged.  I give them an example, I tell the class that I hate small spaces, I hate being crammed together.  If I were a particle in that dry ice I would screaming, (I raise my voice to a scream) "Let me out of here!  I hate being so crammed!"  I tell them that just this short phrase demonstrates an understanding of how the particles are arranged.  

I add this phrase along with a quick picture to my comic strip outline on the front board.  I ask students to complete the next strip by explaining how I would feel (as the particle) as I rapidly change into a gas.  Students say things like "Finally, I am free!" and "Yes, I finally have space to move around."  I like both of these phrases.  I add a similar phrase to my comic strip.

    

A more close up view of the Comic Strip

Explore

30 minutes

Chocolate as a Solid: 

I provide each group with a bag of Candy Melts that are different color.  I use green, pink, blue, purple, red, and regular brown chocolate.  I ask each group to write a list of properties of the chocolate at their table.  As they create a list on their whiteboards, I circulate to listen to conversations.  Groups share their properties which include solid, the color, round, and they keep their shape.  I then ask someone to describe the particles to me.  They say that they are tightly packed and vibrating.  

I pass out a comic strip template to each student and ask them all to create their first comic strip as if they are a particle in one of those pieces of chocolate.  How would they feel?  What would they be saying?  I remind them to try and make it funny, but the purpose is to demonstrate an understanding of what is happening to the particles themselves.  I remind them that things like "I am a solid" are not correct because the particles themselves are not solids, the matter is in a solid state because of how the particles are arranged.  

Melting Chocolate to a Liquid:

As everyone in a group finishes their comic strip, I have one student bring up their bag of chocolate Candy Melts.  I put the bag in the microwave for 30 seconds intervals and remove it at the end of each 30 seconds to check it until it is melted.  I use disposable decorating bags that are used for icing.  These bags are thick so they do not melt.  They are also easiest for creating the candy molds later in this lesson.  

After the chocolate has melted, I send it back with the group to observe properties and create a list for the liquid chocolate.  After I melt the last bag of chocolate (you can melt two or more bags at a time to make it go faster), we discuss the properties of the liquid.  Students have things on their list such as liquid, shape of the the bag, same color, and warm.  I then ask how the particles have changed.  A student tells me they have more space between them now.  Another student tells me they are moving faster.  

I ask students to use this information to create their second comic strip as if they are the same particle as before, but now arranged like the liquid chocolate.  I remind them that things such as, "I melted" or "I am a liquid now" are not accurate because the particle itself has not melted or changed into a liquid, the particles are only arranged differently making the matter be in the liquid form now.  I remind them of these things because I have done this activity several times and these are the common errors in thinking.  Students tend to think the particles are melting as matter melts because they can't see the particles.  

Freezing Chocolate Back into a Solid:

As groups finish their comic strip, I pass out a candy mold to each group.  I explain that when everyone in their group is finished with their comic strip I will cut the end of their bag and they can begin creating their candy mold.  I demonstrate how to twist the top of the bag and squeeze from the top down, otherwise the chocolate will start shooting out of the top and create a huge mess.  I rotate bags of chocolate so that groups have an opportunity to use all of the colors in their candy mold.  I do not allow students to get up and switch bags themselves, as that leads to disruptions and messes.  

    

If chocolate stops coming out of the bag easily, it is because it has started to solidify already.  I have to reheat a couple of bags for about 15 seconds each to keep them warm.  As groups finish filling their molds, I provide them with candy sticks to place in their molds.  This makes it easier to eat at the end.  I then take the molds and place them in the refrigerator.  As I place them in the refrigerator I ask students what that is causing to happen to the particles in the chocolate.  One student tells me it is causing them to come back together.  Another student says they are slowing down again and will be vibrating in place.  I ask students to finish the last comic strip on their paper as if they are still the same particle, but now are being cooled off and moving back together so the chocolate is a solid again.  

Student Comic Strip 1Student Comic Strip 2, and Student Comic Strip 3 were all chosen because they demonstrated a good understanding of the description of the particles.  Although I continued reminding students not to include things such as "I am melting," I still got that on a few.  Comic strip 2 and comic strip 3 above, were both created by ESE students, where as comic strip 1 was created by a regular education student. All levels of students could be successful on this activity which is why I prefer it over a lengthier writing assignment.  I can still get a clear idea of student understanding and they enjoy writing the comics.  

 

Wrap Up

10 minutes

Enjoying the Treats and Sharing Comics:

As the chocolate cools in the fridge for about 5 minutes (this does not take long), we share comic strips.  I ask students to volunteer to share their comic strips on the overhead and read them to the class.  I have a lot of volunteers, but if you do not, you can choose students to share.  I do not comment on things that are not correct at this time, I will write individual notes on the comic strips as I check for understanding.  This is just a time for sharing their creations.  

I take the chocolate out of the refrigerator and pass it out. Students get to eat their treats.