conservation of mass experiment worksheet

Conservation of Mass Experiments

Start with reviewing the difference between physical and chemical changes. (Chemical changes include: gas, color change, precipitate, temperature change, or light). Get some play doh and roll it into a ball. Place it on the scale and ask students if they think the mass will change if you change the shape of the play doh. You could also use legos or anything else you have handy.

Once they’ve seen that physical changes don’t cause a mass change, move on to chemical changes. Here are some labs you can use for different grade levels to teach the law of conservation of mass.

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Lesson 4.1 - Conservation of Mass

Lesson overview for teachers.

View the video below to see what you and your students will do in this lesson. 

Youtube ID: AqrzrUVcA50

Lesson Plan (PDF)   |   Student Activity Sheet (PDF)   |  Student Activity Sheet Answers (PDF)   |   Student Reading (PDF)   |   Teacher Background (PDF)   |   Connections to NGSS (PDF)

Students will be able to make measurements showing that whether the process is a change of state, dissolving, or a chemical reaction, the total mass of the substances does not change. 

Note: In the demonstrations and activities in this lesson, substances will be weighed before and after various processes have occurred – either melting, dissolving, or a chemical reaction. The basic principle students should observe and conclude is that mass is conserved in these processes, so the mass should not change. Students may observe slight variations of plus or minus 0.1 grams, depending on the sensitivity of the balance or whether the mass is actually somewhere between two values. If there is a minor change in mass, explain to students that small differences may be caused by a slight lack of precision in the scale readout, or by errors in the weighing methods, but that the overall results suggest that mass is conserved in all of these processes. 

Key Concepts

• When a substance changes state, the mass of the substance does not change.
• When a substance dissolves in a liquid, the total mass of the substance and the liquid it dissolves in does not change.
• When substances react to form new substances as products, the mass of the products is the same as the mass of the reactants.

NGSS Alignment

• 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.

Note: In this lesson, students measure and observe that mass is conserved during the processes of melting, dissolving, and chemical change. The students will not make a graph. 

• Students check to see whether the mass of ice and water in a cup changes as the ice melts.
• Students also test whether the combined mass of sugar and water changes after sugar is dissolved in the water.
• As a demonstration, students will observe that a precipitate forms in a reaction between solutions of magnesium sulfate and sodium carbonate, and that the mass of the products is the same as the mass of the reactants.

Download the student activity sheet (PDF)  and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan.  

Make sure you and your students wear properly fitting safety goggles.  Sodium carbonate may cause skin and serious eye irritation. Follow all safety precautions regarding the use, storage, and disposal of sodium carbonate. 

Clean-up and Disposal 

Remind students to wash their hands after completing the activity. All common household or classroom materials can be saved or disposed of in the usual manner. 

Materials needed for each group

• 1 Clear plastic cup
• 1 Teaspoon of sugar

Materials for the ENGAGE demonstration 

Materials for the extend demonstration .

• 2 Clear plastic cups
• Sodium carbonate
• Magnesium sulfate (Epsom salt)
• Graduated cylinder

1.  Do a demonstration to show that melting ice in water does not cause the mass of the combined water and ice to change.  

Question to investigate: will the combined mass of water and ice stay the same as the ice in the cup melts  .

• Pour water into a clear plastic cup so that it is about 1/3-full.
• Add 1 piece of ice.

Ask students: 

• If we weigh this cup with the water and ice, do you think the combined mass will change as the ice melts? No.
• Why or why not? Because the ice is just melting. It is still the same amount of water, but it’s just changing from a solid to a liquid. It should have the same mass.

Note: It is possible that some water may evaporate from the cup as the ice melts, causing the contents of the cup to weigh a little less at the end of the process. On the other hand, any water condensing on the outside of the cup could make it weigh a little more. Neither of these factors is likely to contribute much to the combined mass measurements, since very little water will evaporate or condense in the time it takes for the ice to melt.  

• Weigh the cup, water, and ice. Record the combined mass on the activity sheet. 

While the ice melts, have students conduct the experiment below. When they are done with that experiment and the ice has melted, show students the mass of the water and melted ice.  

Expected results 

The mass should be the same. 

Give each student an Activity Sheet (PDF). Students will record their observations and answer questions about the activity on the activity sheet. 

2. Have students weigh water and sugar before and after the sugar dissolves.

Question to investigate:  will the combined mass of sugar and water be the same after the sugar dissolves in the water  , ask students:.

• If you weigh a cup of water and a teaspoon of sugar and then dissolve the sugar in the water, do you think the mass will change? No.
• Why or why not? Because the same amount of sugar is still there. The solid sugar crystals break apart in water as the sugar dissolves, but the individual sugar particles or molecules are still present and do not change as a result of dissolving in the water. The combined mass of the sugar and water shouldn’t change.

Materials for each group: 

• Add water to the cup until it is about 1/4-full.
• Add 1 teaspoon of sugar to the water. 
• Weigh the cup with the water and sugar and record the mass.

Note: Evaporating water could make the water and sugar weigh a little less. This will probably not be a factor since very little water will evaporate in the time it takes for the sugar to dissolve. 

• Carefully swirl the cup to help the sugar dissolve.
• When the sugar is dissolved, place the cup back on the scale to measure the mass.

Expected results

The combined mass does not change.

• Did the mass change? No.

3. Do a demonstration to see if the mass changes during a chemical reaction.

Question to investigate: will the mass change when reactants combine to form products in a chemical reaction  , materials for the demonstration.

• In a clear plastic cup add 50 mL of water and 1 teaspoon of Epsom salt (magnesium sulfate). Gently swirl the cup so that the Epsom salt dissolves.
• Measure the combined mass of the cup with the Epsom salt solution in it. Tell students the mass and have them record it.
• To another cup, add 50 mL of water and add 1 teaspoon of sodium carbonate. Gently swirl the cup until the sodium carbonate dissolves.
• Measure the combined mass of the cup with the sodium carbonate solution in it. Tell students the mass and have them record it.
• Have students add the two masses together and record and announce the sum. 
• Hold the cups up so students can see them and then slowly and carefully add the sodium carbonate solution to the Epsom salt solution.

A white solid will form. At first the solid may appear or look like clouds of white particles floating in the liquid, but the particles should eventually settle out to form a solid precipitate at the bottom of the cup.  

Tell students that a chemical reaction took place and that a new substance, a solid, was formed.  

• Do you think the total mass of the two cups, the combined solutions, with the white solid will be more, less or the same as it was before the reaction took place? Same.

• Place both cups on the scale to measure the total mass. 

The total mass should be the same as the sum of the individual masses recorded before the contents of the cups were combined and the reaction took place.

Explain that the reactants have been transformed into a new substance, but that all the individual atoms making up the reactants are still present in the products. That’s why the mass stays the same.

4. Show an animation to help explain why mass is conserved in melting, dissolving, and in a chemical change.

Show the animation  Conservation of Mass in Physical and Chemical Changes.

Explain that whether a process involves melting, dissolving, or a chemical reaction, all the atoms that were there before the process takes place are still there after any changes have occurred, so the overall mass stays the same. 

5. Show an animation to help explain why mass is conserved when water is frozen.

Remind students that they observed that the overall mass of water and ice stayed the same as the ice melted.

• When water freezes to form ice, it takes up more room in the container, but does its mass change?  Even though the volume of water changes as it becomes ice, the mass of the water should remain the same before and after it turns into ice.

Show the animation  Mass is Conserved in Freezing . 

Explain that even though water takes up more room when frozen, the same number of water molecules are still there so the mass stays the same. 

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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.

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.”

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.

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.”

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.”

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.”

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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Law of Conservation of Mass

The Law of Conservation of Mass is a fundamental concept in chemistry, stating that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. According to the law, the mass of the reactants in a chemical reaction equals the mass of the products . Further, the number and type of atom s in a chemical reaction is the same before and after the reaction.

Definition and Statement of the Law of Conservation of Mass

The Law of Conservation of Mass was first articulated by Antoine Lavoisier in the late 18th century. It asserts that the total mass of a closed system remains constant over time. This principle is widely applicable in chemical reactions and also applies to other disciplines.

Applicability of the Law

The law holds true in chemical reactions under ordinary conditions. This is because chemical reactions only involve electrons and do not affect the identities of the parts of the atom .

However, the Law of Conservation of Mass does not hold in nuclear reactions, where mass can convert into energy (and vice versa) according to the principle of mass-energy equivalence as proposed by Einstein in the theory of relativity. This conversion occurs in nuclear fission and fusion reactions and some forms of radioactive decay.

Also, the law applies to isolated systems. If matter or energy enters or exits a system, mass may not be conserved.

Historical Overview

The concept of mass conservation dates back to ancient Greece. Mikhail Lomonsov, outlined the principle in 1756. Lavoisier gets credit for formalizing the law in 1773. His work disproved the then-popular theory of phlogiston , a supposed fire-like element released during combustion. Lavoisier demonstrated that combustion results from chemical reactions with oxygen, not from releasing a mysterious substance, and that the mass before and after the reaction was the same.

Examples in Chemical Reactions

Chemical reactions clearly illustrate the Law of Conservation of Mass. Chemists apply the law in balancing chemical equations.

• Combustion: In a simple combustion reaction , such as burning methane (CH₄), the total mass of methane and oxygen equals the mass of the resulting carbon dioxide and water. CH 4​ + 2O 2 ​→ CO 2 ​ + 2H 2 ​O (4 H, 1 C, 4 O atoms on each side of the reaction arrow.)
• Synthesis: When hydrogen and oxygen gases react to form water, the mass of the two gases equals the mass of the water produced. 2H 2 ​+ O 2 ​ → 2H 2 ​O (4 H and 2 O on both sides of the reaction arrow.)

Examples in Organisms

In biological systems, the law applies to metabolic processes. For example, in photosynthesis , plants convert carbon dioxide and water into glucose and oxygen. The total mass of carbon dioxide and water used equals the mass of glucose and oxygen produced:

6 CO 2  + 6 H 2 O → C 6 H 12 O 6  + 6 O 2

On a larger scale, the law applies to the mass of a human body, which encompasses numerous chemical reactions occurring at once. If you maintain a constant weight, the mass you gain from breathing, eating, and drinking equals the mass lost through breathing, perspiration, urination, and defecation.

Examples in Ecosystems

In ecosystems, the law is evident in nutrient cycles, such as the carbon cycle. Carbon atoms are conserved as they move through different components of the ecosystem, including the atmosphere, hydrosphere, lithosphere, and biosphere. For example, the photosynthesis reaction takes carbon from the air and fixes it into a glucose molecule. Photosynthesis does not create mass, nor is any lost in the process.

• Okuň, Lev Borisovič (2009). Energy and Mass in Relativity Theory . World Scientific. ISBN 978-981-281-412-8.
• Pomper, Philip (1962). “Lomonosov and the Discovery of the Law of the Conservation of Matter in Chemical Transformations”. Ambix . 10 (3): 119–127. doi: 10.1179/amb.1962.10.3.119
• Whitaker, Robert D. (1975). “An historical note on the conservation of mass”. Journal of Chemical Education . 52 (10): 658. doi: 10.1021/ed052p658

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Science project, conservation of mass.

Grade Level: 9th - 12th; Type: Chemistry

The goal of this experiment is to learn about conservation of mass by conducting a chemical reaction inside a sealed environment. Students can weigh the reactants before, during and after the reaction to determine if mass was conserved. The difference between weight and mass will be considered.

Research Questions:

• What chemical reaction occurred in this experiment? Can you write the equation and balance it?
• What is the difference between mass and weight?
• According to the laws of conservation of matter, the end mass of the reactants should be the same as before the reaction took place. If your end weight was lower, can you explain why?
• If the weight decreased after the gas evolved, how do you explain thisDoes the weight increase later? Why?

According to the principal of conservation of mass, the mass of the products of a reaction should be the same as the mass of the reactants if the reaction takes place in a sealed system. This is largely synonymous with conservation of matter. In this experiment, a sealed system is created by a sealed zip-lock bag. Students can measure the weight of the bag before, during and after the reaction. The evolution of gas inflates the plastic bag in all directions, and gives rise to interesting questions about the difference between mass and weight.

Check to see if your teacher can supply these small amounts of reagents and let you use a triple beam balance.

• Quart size zip-lock bag
• 10 ml phenol red indicator
• Small paper cup or film canister
• Small graduated cylinder
• 25 ml water
• 5.0 g of solid CaCl 2
• 5.7 g of solid Na 2 HCO 3

Experimental Procedure:

• Weigh a 1 gallon zip-lock bag. Write down this weight.
• Measure 25 ml of water and the water to the cup or film canister. Using a graduated cylinder, measure 10 ml of of phenol red. Add this to the container and water. Weigh the container, water and phenol red. Write down this value. 
•  Measure 5.0 g of solid CaCl2 and put it in one corner of the plastic bag.
•  Weigh 5.7 g of solid NaHCO3 and put it in the other corner of the bag, taking care to isolate it from the CaCl2.
•  Place the cup of water in the center of the bag, taking care to keep the reagents in their separate corners.
•  Squeeze as much air as possible out of the bag. Seal the bag as completely as possible. There should be a closed system in the bag.
• Tip the water and combine the ingredients by massaging the outside of the bag. The bag will get warm and a gas will evolve. Record your observations of this reaction.
• Weigh the bag as the reaction is occurring. Weigh the bag again when the gas has evolved. Weight the bag after the heat dissipates.

Terms/Concepts: Conservation of mass; Conservation of matter; Weight, mass 

References:

• Gonick, Larry and Craig Criddle. The Cartoon Guide to Chemistry. Collins Reference (2005) 
• Moore, John T. Chemistry for Dummies. For Dummies (2002).
• Conservation of mass ( http://en.wikipedia.org/wiki/Conservation_of_mass )

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Conservation of mass Worksheet

Subject: Chemistry

Age range: 11-14

Resource type: Worksheet/Activity

Last updated

1 February 2021

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Revision of chemical reactions and conservation of mass using diagram based equations.

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