Changing Matter: Is Weight the Same or Different?

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Objective

SWBAT provide evidence to support their conclusion that the amount of matter present is conserved or is not conserved when matter changes state.

Big Idea

Students conduct a hands on investigation to determine how matter, changing state, effects the property of weight.

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-PS!-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 is directly linked to standard 5-PS1-2 through the investigation that students will be conducting.  They will be making measurements to determine if weight/mass changes if matter changes state.  They will graph their results as well to share their findings with others.  

Lesson Goal: 

The goal of this lesson is for students to be able to collect evidence to support the idea that weight/mass of matter does not change when it changes state.   

Success Criteria:

Students will demonstrate mastery by making accurate measurements of matter in the solid state and comparing it to measurements of the same matter in the liquid state.  They will test the theory on several different items to collect more evidence to support their findings.  

Preparing for Lesson:

Warm Up:

  •  A cup with a stick of butter in it for students to observe and record properties of 
  • Whiteboard and marker for each group 

Guided Practice: 

Explore: 

Wrap Up: 

  • Freezer 

Warm Up

10 minutes

Purpose of the Warm Up: 

I begin today's lesson by having students identify an an unknown substance (butter) using properties.  I am doing this to review physical properties of matter, as well set the background for the comparison of properties from matter in a solid state, to those of the same matter, once it is melted in the liquid state. I use butter for the lesson because one property that changes significantly between solid and liquid, is the amount of space it takes up in the cup.  You could use any item that melts quickly.  

Using Properties to Identify the Mystery Substance: 

I hold up a cup with a stick of butter in it for the class to see.  I tell students that I found the item in the classroom that morning and I do not know what it is.  I ask students to discuss with their group, what they believe the item is, and to create a list of physical properties that helped them come up with their answer.  We have already talked about physical properties when we completed the classification lesson from unit 1.  Each group already has a whiteboard and marker to record their list.  I rotate around to allow groups to observe the item more closely and to listen in to conversations.  

After a few minutes, I bring the class back together and ask for each group to share their thoughts on what the object is, and their list of physical properties. 

All groups identified the item in the cup as butter.  I tell them that they did an excellent job of using observations to correctly identify the object, it is butter.  

Guided Practice

10 minutes

Recording Properties as a Solid:  

I place the "Is it the Same or Different - Comparison Chart" on the overhead so all students can see it.  I ask students to copy in the rectangle and arrow which are blank.  While they begin copying, I take the butter to the microwave and heat it for 45 seconds.  I do not remove it from the microwave yet.  

I record a few of the properties that groups identified in the first rectangle box of the comparison chart.  I ask students to copy the same list.  I write things such as yellow, solid, smooth, cold, in a rectangular shape, and tall.  I point out the property described as tall and explain to students that the butter is almost sticking out of the cup.  If this isn't noted now, it may be overlooked in the next section of the chart where they compare the solid form of the butter to the liquid.  Making sure to note it just before removing the butter from the microwave will almost guarantee it is one of the first changes they notice.   

Comparing Properties of the Solid to That of the New Liquid:  

I remove the cup from the microwave and circulate so each group can get a good look at the butter now.  I ask them to create a T-chart on their whiteboards to describe properties that have remained the same and properties that are different now that it is melted.  I circulate while groups record their responses on white boards.  After a couple of minutes, I ask students to hold up white boards. The only similar property noted was the color.  Properties that changed were the state, the shape, the height or amount of space it takes up, and some groups noted that it will flow now but it didn't before.  

                                     

For a more close up view of the whiteboard you can see it on the picture of whiteboard response for comparing solid butter to liquid butter

We move to the comparing chart in our notebooks and begin placing these properties in the correct column, either similar property or different property.  I write them in my notebook on the overhead while students copy them.  I always show my notebook on the overhead to assist the ELL and ESE students in my class with spelling and recording accurate information.  

                                          

                                     You can see the Student Notebook Picture more closely here. 

 

Explore

30 minutes

Predicting the Outcome: 

After reviewing the list of similar properties and different properties from above, I ask students how they think the change affected the weight/mass.  Something that was not mentioned.  I point out that it changed from a solid to a liquid, and that it went from taking up a lot of space to only taking up a very little.  What would that do to the weight/mass?  

While students think about this, I pass out a Is It the Same or Different - investigating weight.  I ask all students to write their prediction in at the top of their investigation sheet.  I tell the class that they will be investigating the weight/mass of three different items as solids, and then again after these items change from a solid to a liquid to see how changing state affects the weight/mass.  I circulate to make sure all students have filled in their prediction and note that the majority of students believe that the weight will be different.  

Investigating

Before I provide each group with their materials, I review how to properly use the balance.   Taking the time before passing them out, will hopefully eliminate error and allow students to work successfully in small groups without my assistance.  I call on a student to review the correct procedure for using the balance with me.  As she goes over the steps, I model what she is saying by doing it with the balance.  

After reviewing the correct procedure, I provide each group with a tray that contains 1 balance (make sure they are working and have all weights prior to the activity), an extra 50g weight (the butter with the cup is heavier than the 100g that comes with each balance), 1 cup of ice, 1 cup with a Hershey's bar broken down into pieces, and 1 cup with a stick of butter in it.  I use plastic measuring cups instead of glass because glass is heavy and I have found that if using glass, there are not enough weights on the balances for students to measure the weight.   When I used glass, students had to pass around weights to share which caused the lesson to take twice as long.  I have also tried regular plastic cups and they began to melt when heated so be sure the plastic is thick. I chose chocolate, butter, and ice because these items melt quickly and freeze relatively quickly.  You could use any items that fit this description, but I do recommend using at least 3 items so students can see the outcome is true for a variety of types of matter. 

I remind students they should be completing their data chart as they complete the investigation.  I circulate to ensure that students are correctly making their measurements and recording their units of measure with it.  

Video of students measuring mass of solids

As students finish their measurements, I allow one group at a time to go up and microwave their cups in 30 second intervals.  As they microwave, I keep a close eye on them so that I can make sure they are not putting in the wrong time, and to make sure that the items are melting completely.  My students have used the microwave in previous lessons so they are familiar with it.  If your students are not, you may want to the do the microwaving for them.   

After microwaving, students return to their seats to measure the substances again, now in their liquid form.  

Video of students measuring mass of liquid

As students begin measuring and comparing, I start to hear some surprised "it did stay the same" and "of course, it didn't change it is still butter, so why would the weight change?" This discovery is nice to hear because students were able to come up with it on their own, and even adjust their own thinking based on the new information they have gathered through the investigation.  

Wrap Up

10 minutes

Compare Results:

I ask each group to share their findings with the class.  The two photos of student work below are a good snap shot of what all students found.  All groups found that the mass/weight stayed the same.  A couple of groups were off by one or two and I explained that one or two grams is not a big deal because of how small a gram is.  That they could have thought the balance looked more balanced with that extra gram the first time, and then the next time thought it looked more balance without it.  

   

After each group shares, I ask them what they think the results would be if we took the liquids and froze them back into solids.  Students believe that the weight/mass would remain the same.  This new prediction has verified that student thinking has changed because the majority of their predictions for the first test between solid and liquid, were that it would be different.  Now the majority of students believe it would be the same going from a liquid back to a solid.  I collect all cups on a tray, and place the entire tray into the freezer.  If you do not have a freezer in your classroom, you can collect them and carry them down to a freezer later in the day.  It is important to remember to have groups write their group number on the cups so that they are sure they get their own cup back the following day.  

The Following Day:  

Remove cups from the freezer and have students measure the weight of the new solid.  This allows them to see that no matter how many times it changes back and forth, the weight will remain the same.  After remeasuring the new solid, students answer the conclusion questions at the end of the investigation sheet. 

Here is a Picture of completed investigation sheet to see the results and information this group got.  You can see that this group got different results for the butter between the solid and liquid state.  They explained at the bottom of the sheet the error that occurred was due to me spilling the butter and having to give them new butter.  They did find that the weight for the butter stayed the same when changing the liquid butter back to a solid.  

All groups found that the weight/mass of the chocolate and water stayed the same when they changed from a liquid back to a solid.  I did however, have about 4 groups between the two classes that all found that the butter had changed weight/mass after refreezing it to a solid.  Their measurements were off by more than 5 grams which is a significant difference.  We discussed possible reasons for this, but I did not have an exact answer for this.  The other 6 groups, found that it stayed the same so the majority did find accurate results which led us back to a review about why scientists conduct repeated trials.  

Graphing to Share Results 

For homework, students will graph the results of their findings to share with others.  They will create a triple bar graph that shows the weight/mass as a solid, liquid, and then again as a solid after refreezing it.  

  

The first graph shows that all the measurements are accurate, however, this person marked their key wrong.  This was a common mistake I saw when checking graphs.  Most students listed the bars as being water, butter, and chocolate because they are so used to labeling them as the items being tested.  I had to have many students change it to show that the bars are actually the solid, then liquid after melting, and then solid again after freezing.  The second graph is the group that I spilled the butter so it looks a little off for the butter.