Changes in States of Matter: A Demonstration for Your Classroom

This is a one gallon milk jug after the activity.
It's all caved in now!

Back when I taught seventh grade science, I always used this demonstration in my changes in states of matter unit. I liked it because it was easy, didn’t require many supplies, needed very little prep work, the students enjoyed it, and it got my students thinking and talking about the changes in states of matter. Can’t beat that right?

Activity Overview:

In this changes in states of matter activity, boiling water is added to an empty milk carton. Once sealed, the milk carton significantly contracts and crumples in on itself. The activity shows students two changes in states of matter (vaporization and condensation), and with the right questions, it gets your students thinking about and discussing particle movement in the different states. If done as a demonstration, it takes approximately one 45 minute class period. If done as an experiment, it could take two 45 minute class periods.

Needed Supplies:

One of the best things about this activity is that it requires minimal supplies and all of those supplies are inexpensive and easy to find. Here’s what you need:

• An empty one gallon milk carton with its lid: While it’s possible to use other containers and container sizes, I recommend using a regular ol’ plastic gallon size dairy milk carton. I’ve used half gallons and that size doesn’t really show a whole lot of crumpling. Other plastic cartons can be too rigid and don’t show the crumpling at all. And some cartons might even melt and get all gooey and messy on you. Plus they can give you some nasty burns. So yeah, just use a gallon milk carton.
• Water: Different amounts can be used, but I’ve found that 1.5 liters works best. Don’t use less than 0.5 liters and don’t fill the carton more than halfway.
• A heating source to boil the water: I like using a hot plate because students can easily see the bubbles and steam coming off of the water as it’s boiling. You can use an electric kettle or a microwave or a Bunsen burner. Or you could even go caveman and build a big bonfire in the middle of your classroom. Just kidding. Please don’t do that. 
• A heatproof container to boil the water: Because you can’t boil water without one.
• A funnel: It’s optional, but can be nice to have when pouring the water into the carton. Plus you can wear it as a hat when you’re not using it.
• An ice bath: No, it’s not for you to sit in. The ice bath is optional, but can be used as another part of the activity. 
• Safety materials: It’s always important to model laboratory safety.

Demonstration Instructions:

This activity can be used as a demonstration or an experiment. In my class I’ve always used it as a demonstration because 35+ middle school students all messing with boiling water at the same time in a classroom that’s not really set up for laboratory purposes didn’t sound like a good time.

Here are some demonstration directions you can use:

1. Review the changes in states of matter with your students. 
2. Explain to your students that you will be boiling water, adding it to an empty milk carton, and sealing the carton with the lid. 
3. Have students make predictions about what will happen to the carton.
4. Begin heating the water. While the water is heating, ask questions about what is happening to the water particles and what change in state of matter is occurring and why. It’s vaporization, ya’ll. 
5. Once the water is boiling, carefully pour it into the empty milk carton. Use a funnel if you have one or skip it if that’s how you roll. Immediately put the cap on the milk carton. Make sure it’s on there tightly.
6. Have students observe the changes and make observations about what they see. Ask them to try to explain why this is occurring. (Here’s why the carton crumples: As temperatures increase, air pressure and air volume increase too. As temperatures decrease, air pressure and air volume decrease as well. The difference between the air pressure on the inside and the outside of the carton along with the decreasing volume of the cooling gas inside of the carton cause the carton to collapse.)
7. If you have an ice bath prepared, now’s the time to place the carton in the cold water. The cold water will increase the speed at which the carton crumples. If you don’t want to do the ice bath part, well that’s just fine and dandy. Skip it and move on to the next step.
8. Point out the tiny droplets of water on the insides of the carton. Ask students to explain where those droplets of water came from and why they are there. (Condensation.)
9. Discuss the activity and the changes in states of matter with your students. Maybe have your students draw the particle movement during each part of the activity. 
10. That’s it. All done. 

My Changes in States of Matter Demonstration is in my store. It has full directions, student sheets with many discussion questions, and an answer key. Get my Changes in States of Matter Demonstration here.

Experiment Ideas:

Like I said, I do this as a demonstration. Because, you know, 35+ middle school students playing in boiling water can be a titch terrifying. Even if they aren’t actually playing in the boiling water. That’s just what I envision happening when I think about my students doing this activity as an experiment. But, some teachers are fortunate enough to have smaller class sizes and a classroom that is setup for this kind of thing.

Here are some experiment ideas:

• Test which amount of water causes the milk carton to collapse the most.
• Test different container sizes to see which collapses the most. 
• Test different container materials to see which carton collapses the most. (Test the materials yourself first to make sure there aren’t any melting issues.)
• Try placing the filled cartons in different locations to see which causes it to collapse the fastest. (Think: refrigerator, freezer, ice bath, sunny windowsill, under a fluffy towel, on a table…

Well, I hope you and your students enjoy this activity. Remember, my Changes in States of Matter Demonstration is available in my TPT store and comes with full directions, student sheets with plenty of thought-provoking questions, and an answer key. 

If you want more materials for your changes in states of matter unit, check out my Changes in States of Matter Bundle. It has interactive notebook pages, bell ringers, activities, stations, projects, worksheets, and an assessment. Woo-hoo! If you're looking for a workbook, check out the Changes in States of Matter Physical Science Workbook for Middle School available on Amazon! Learn more about the workbook.

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Why Pre-Assessments Are Always a Good Idea: My Ruler Story

In the summer before my first year of teaching science I remember talking to the other science teacher. She casually mentioned that I should teach my students how to use a ruler before doing any labs or activities because many of them wouldn’t know how to measure properly. We were talking about my seventh grade students. Seventh grade. I remember learning how to use a ruler in early elementary school. How could seventh graders not know this basic skill? Surely my students knew how to use rulers.

Just in case my fellow science teacher was right, I decided to add a couple of questions about measuring with rulers to my beginning of year exam. Weeks later, when my students took that pre-assessment, my mind was blown. Over half of my students didn’t know how to use a ruler. They didn’t know you need to start at the first line of the ruler and not at the edge. Furthermore, they didn’t know a ruler can be used to measure in a unit other than inches. Even the students who knew that rulers can measure in centimeters had no idea that rulers are marked with millimeters too. It was like rulers were some rare, mythical object instead of a basic tool found in most classrooms.

Pages from my students' INBs about using rulers properly.
Get these Metric Length INBs in my store.

Thankfully, I became aware of the issue in the first week of school and could easily and quickly fix it. We had a special lesson on rulers and students added measurement and ruler information to their INBs. I made sure my students could use rulers properly before proceeding to the more complex stuff in science. Any time we had a lab or unit involving length, I reviewed ruler skills to make sure my students still had it down. Had I not known about my students’ measurement problems, I would have spent much of the year wondering what was up with my students’ answers and why lab and activity results were wonky. The pre-assessment saved my students from frustration and lost learning time.

This experience taught me to never assume that students come to class with certain knowledge and skills. Whenever possible, I check to see what students know before beginning a new lesson or unit. If students don’t know the basics, then they get overwhelmed quickly, shut down, and don’t learn. Doing a precheck can be as easy as having students raise their hands in answer to a yes or no question, eavesdropping on student discussion of a topic, or adding a question to students’ bell work. If you notice that students don’t understand something, address it before moving on and introducing new content. Knowing about the issue right away allows you to fix it before it gets in the way of student learning.

Have your classes ever shocked you by not knowing something? What was it? When did you find out they didn’t know it? Were you able to address the problem? Share your story in the comments section!

Need measurement resources for your classroom? Check out the some of the metric length resources from my Teachers Pay Teachers store.
Metric Length and Ruler INB Pages
Metric Length Worksheet
Measurement in Science Stations: Tools and Metric Units

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How to Teach Laboratory Safety to Middle School Science Students

The very first unit I teach to my seventh grade science students is laboratory safety. Teaching lab safety as your first unit immediately sets your students up for yearlong success in science class. Students love experiments and often learn the most from that kind of hands-on activity. Therefore, being able to safely participate in science class at the beginning of the year is vital. Another bonus is that the unit is short and the content is straightforward (i.e. easy), so it is a great way to introduce and practice class procedures like note-taking, working in a group, participating in an activity, handing in homework, taking a quiz, etc.

How do I plan my lab safety unit?

Start with a lab safety contract! Safety contracts are filled with all of the important safety stuff students need to know. Use one to build your unit. When I first started teaching middle school science, I used Flinn Scientific’s safety contract. (Just Google “Flinn Scientific Safety Contract” and what you need will pop up, available for free. I know there is a high school and a middle school version out there and both of them come in English and Spanish.) However, not all of the Flinn Scientific material applied to my students—it mentioned chemicals and equipment we wouldn’t be using. For my own lesson planning purposes, I printed a copy of the safety contract and highlighted the most important information and crossed off what wasn’t going to be relevant to my students that year. That helped me focus on what I wanted my students to come away knowing. Using my highlighted safety contract, I wrote a list of lab safety rules that encompassed the most important safety information. Then I created my lab safety quiz. Once you have your safety rules written and your assessment made, you’re ready to decide how you’re going to teach the material. Note-taking? Activities? Scenarios? Choose what works best for you, your teaching style, and your group of students.

What lab safety rules should I use?

Like I mentioned above, you can construct your own lab safety rules using a lab safety contract. Alternatively, you can use the rules I wrote for my own students. They are listed below. You’re welcome ;)

1. I will always take the time to read and understand all laboratory procedures before beginning.
2. I will carefully follow all directions and will ask the teacher if I do not understand something.
3. I will not touch any laboratory materials before being told to do so.
4. I will keep my area clean and clear of everything except laboratory materials. 
5. I will properly wear all required safety items, such as goggles or aprons, for the duration of the laboratory activity.  
6. I will wear appropriate clothing on lab days. I will wear closed toed shoes. I will tie back long hair if applicable. I will not wear baggy clothing or jewelry. 
7. I will only work when the teacher is present. 
8. I will not eat, drink, or chew gum during the laboratory activity. 
9. I will not run or engage in any horseplay during the laboratory activity. 
10. I will tell the teacher immediately about any injuries, spills, or broken items. 
11. I will not take any of the laboratory materials without permission from the teacher. 
12. I will completely clean my area and appropriately return laboratory materials before leaving the classroom. 

How many days long should my lab safety unit be?

I always make my lab safety unit last no more than one week long. That gives us more than enough time to introduce, practice, and assess the unit. And remember, I also use this time to familiarize students with classroom procedures, which saves us oodles of time later in the year. Five 50 minute class periods (or three 90 minute block periods) is the most I’ve ever needed for this unit. In my opinion, the optimal amount of time to spend on the safety unit is four 45 minute long class periods.

What does a complete lab safety unit look like?

Below you’ll find a breakdown of my own tried and true lab safety unit. I’ve taught this unit using various bell schedules—(45 minute classes, 55 minute classes, and 90 minute classes). The unit description below is for four days of 50 minute class periods.

Day One:

Start class with a science safety warmup (also called a bell ringer) to see what students already know. Discuss student answers. As a class, read through and discuss lab safety contracts and have students sign theirs. Send the contracts home and have parents sign the contracts as homework.* Make it clear that students will not participate in any labs or experiments until their signed contracts have been handed in.

*The lab safety contracts are due by the end of the week. Students are reminded throughout the week to hand them in.

Day Two: 

Begin class with another warmup about lab safety. Discuss student answers. Use a PowerPoint to guide student note-taking about lab safety. I include the following notes sections: Before the Lab, During the Lab, After the Lab, and Other Safety Information. Here is a video of the interactive notebook pages I use with my students. You can get these INB pages and a PowerPoint here.

Day Three:

Begin class with a warmup about lab safety. Discuss student answers. Review the material students learned the day before. Then it's activity time. Students can practice the lab safety rules in small groups with a fun scenario activity. Then you can send students home with this fun safety bookmark that'll function as a study guide. Alternatively, instead of the scenario activity, you can have students color and complete the lab safety bookmarks as a beginning of the year safety activity. (Take a look at the example safety bookmark below.)

Day Four:

Begin class with a warmup about lab safety. Discuss student answers. Review lab safety information. Students complete their lab safety quiz. If there is time at the end of class, then go over the quiz answers together. 

***Cross your lab safety unit prep off of your to-do list! Get all of the lab safety resources mentioned in this post in one awesome time-saving bundle. Plus, ALL of the lab safety resources come in both English AND Spanish.

What do I do before each science experiment in the future?

Before Every.Single.Science.Experiment we review general safety information and safety information that is particularly relevant to that experiment.

Well, that’s my lab safety unit! I hope it helped you plan your own unit or gave you a clear picture of how to use my safety unit in your own class. 

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