Teaching Law of Conservation of Mass in Fifth Grade

Teaching law of conservation of mass in fifth grade? Try these hands-on activities! Kids experiment with physical and chemical changes. In closed systems, they find that the mass is the same.

Teaching Law of Conservation of Mass in Fifth Grade Cover

Teaching Law of Conservation of Mass in Fifth Grade

Our favorite fifth grade teacher sat at the back table with his teaching partner. “Now we’ll continue planning our physical science activities,” he said. “Last week we planned our introduction to matter. At the same time, we tackled a lab on properties of matter. Additionally, we finalized physical and chemical changes. What’s on tap for today?”

Mrs. Washington looked at the standards. “Another matter standard.” She read it aloud:

NGSS 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.”

Mr. Grow scratched his chin. “Actually, we don’t need to unwrap this standard too much. Sounds like we’ll be teaching law of conservation of mass.”

Mrs. Washington nodded. “I poked around on the Internet and found some related science resources.” She turned her laptop so her co-teacher could see.

“Scaffolding begins with simple physical changes. Then kids move into chemical changes.”

Teaching Law of Conservation of Mass for Physical Changes

She scrolled to the first activity for teaching law of conservation of mass.


“As you can see, kids work in their lab groups. First, they find the mass of five crackers. Then they smash them up. Again, they measure.”

Mr. Grow smiled. “Bet they’ll love the smashing part. Although this isn’t mentioned in the standard, it’s a good start to teaching law of conservation of mass.”

When teaching the law of conservation of mass in fifth grade, begin with crackers. Kids find that no matter is gained or lost when they are broken.

Sugar Water

Mrs. Washington scrolled to the next activity. “Here,” she said, “kids get a lot of practice measuring with graduated cylinders. First, they measure 10 milliliters of sugar. Second, they find its mass. Next, they measure and mass 50 milliliters of water.”

“Hey,” Mr. Grow inserted, “that’s a great time to talk about how one milliliter of water has a mass of one gram.”

“Right. So 50 milliliters of water has a mass of 50 grams.”

Mr. Grow looked at the activity and continued the directions. “After that, they mix the sugar and water. Of course, the sugar dissolves. Hmm, I can see where this is going.”

“But the mass remains the same!” Mrs. Washington exclaimed.

Teaching the law of conservation of mass in fifth grade? Try this solution of sugar water!

Water to Ice

Again, the teachers scrolled down.

“In the next activity, kids measure 30 milliliters of water and mass it. As you can see, they subtract the mass of the container. Great lab practice. Anyway, afterward, they cover the graduated cylinder with plastic wrap. And the teacher pops it into the freezer.”

“So the lab is finished the next day?”

“Correct. They mass the ice the next day. Actually, they use the same lab sheet for all three physical change activities. At the end, they draw conclusions. Initially, they just circle whether the masses are the same or different. Then they deduce whether mass changes during a physical change.”

“Aha,” said Mr. Grow. “So they’re basically teaching law of conservation of mass to themselves. I really like this.”

When water freezes, it has the same mass.

Teaching Law of Conservation of Mass for Chemical Changes

“Next,” said Mrs. Washington, “kids dive into chemical changes. Now it’s even harder to believe the law of conservation of mass.”

Baking Soda and Vinegar

“But look at this,” said Mr. Grow. “In this lab, kids compare the mass after a chemical change. The ingredients are simple: baking soda and vinegar. For the first part of the experiment, they use an open container. Then, for the second part, the container remains closed. Cool!”

Mrs. Washington smiled and nodded. “Yes, and this hits the graphing portion of the standard. I wondered how that would be achieved. On this lab sheet, they graph before and after. Then they compare open and closed systems. Perfect.”

To better understand the law of conservation of mass, kids experiment with baking soda and vinegar in open and closed systems.

The pair looked more closely at the directions. “We’ll need some tiny cups. After the kids measure the vinegar, they place them a baggie with the baking soda. In the final part of the lab, they pour the vinegar while keeping the baggie sealed.”

Hydrogen Peroxide and Yeast

Mrs. Washington scrolled down farther. “Looks like the final two activities are optional,” she said. “In the first extension, kids read about the law of conservation of mass. Based on Antoine Lavoisier’s 1789 discovery, it states that mass is neither created nor destroyed. In other words, mass remains the same.”

Mr. Grow looked at the activity. “I see. Here, they take a look at volume. If they were paying attention, they would have already noticed it. But this fun experiment illustrates it without a doubt. Kids or the teacher pour hydrogen peroxide into a bottle. Then they add yeast that’s been dissolved in warm water. During the chemical reaction, bubbles flow right out of the top of the bottle. Obviously, volume can change.”

“Fun! You know those sudden reactions really engage our students.”

In this demonstration, kids find that while mass is conserved during a chemical change, volume is not.


Finally, the teachers looked at the last activity. Staring at the picture, Mr. Grow asked, “How is that possible? Wouldn’t popped and unpopped popcorn have the same mass?”

Mrs. Washington chuckled. “You weren’t paying close attention,” she said. “The principle can only be guaranteed in a closed system. Think about that hole in the top of the popcorn bag. When it pops, steam escapes.”

Mr. Grow rapped the palm of his hand on his forehead. “Of course! Well, this is a great finale. And I’ll bet our kids would like to eat the popcorn as well.”

Now both teachers were grinning. Yes, teaching the law of conservation of mass in fifth grade would be a hit.

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