experiments to test the law of conservation of mass

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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experiments to test the law of conservation of mass

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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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Conservation of Mass Lab: Explained & Answers

Conservation of Mass Lab: Explained…

The Law of Conservation of Mass is an important principle to the scientific community and the world of chemistry. The objective of this lab was to verify if this law holds true. This law is beneficial in chemistry as it allows us to predict the final products of a chemical reaction. In this lab, we had verified this law by performing a reaction of sodium bicarbonate and acetic acid. This was done in all three trials, wherein each trial the reaction was performed in a different environment. The first time, it was in an open environment, the second time it was sealed and the third time it was sealed with a balloon. The reaction took place in a plastic 300ml juice bottle with 15 g of sodium bicarbonate used in each trial. We measured the mass of the reactants and containers before the experiment and measured the mass of the products and containers at the end of the reaction. If the law of Conservation of Mass holds true, these masses should be the exact same. From our tests, the masses were not the same but very similar, especially in trial #2 where the bottle was sealed with a cap. There was a difference when the bottle was open, signifying that there was a gas produced in the reaction which escaped. From our results, we can verify that the law of conservation of mass holds true while accounting for human error.

Introduction:

Purpose: The purpose of this lab is to verify the Law of Conservation of Mass holds true

Background:

The Law of Conservation of Mass was developed by the french chemist named Antoine Lavoisier, who had a discovery in 1789 that stated, mass is neither created nor destroyed in chemical reactions. This principle suggests that all atoms on earth have cycled through different forms but were never created nor destroyed in that process. If all the reactants and products are taken into account, he discovered that mass is always preserved. Many other scientists have confirmed Lavoisier’s conclusion, and it is now regarded as scientific law.

This means that the mass of the reactants and products of any chemical reaction in a closed system will be the same. The Law of Conservation of Mass is very important to the scientific world as it allows scientists to predict the amount of product that will be made from a reaction. In this lab, we will be looking at the reaction of baking soda (sodium bicarbonate) and vinegar (acetic acid). This reaction is of a household base and acid, which means a neutralization reaction would occur, because of this we can predict a type of salt and water will be created.

Experimental Design

Experimental Question:

How does the final mass of the products compare to the initial mass of the reactants following a chemical reaction in different experimental conditions?

Independent Variable: The independent variable is the environment or system the chemical reaction takes place in.

Dependent Variable: The dependent variable is the mass of products created by the chemical reaction in different experimental environments.

Controlled Variable: The control in this lab was the initial mass of the reactants as the same amount of reactants were used in each trial. (The only difference in mass was the added covers like the bottle cap and balloon in trials 2 and 3)

If the environment of the chemical reaction is changed, then it will have an effect on the final mass of the products, because the Law of Conservation of Mass stipulates that the mass of the reactants must be the same as the mass of the products in a closed system reaction.

Materials Used:

-1 Electronic Balance

-1 100 mL graduated cylinder

-1 Scoopula

-1 Weighing paper

-1 300 mL juice bottle with cap

-1 Graduated cylinder

-25 g Baking soda (in a 100 mL glass beaker)

-60 mL Vinegar (in a 100 mL glass beaker)

-Recorded the mass of the empty juice bottle without the cap, then poured 15mL of vinegar into the juice bottle. Mass of this was recorded

-Weighed 5g of baking soda onto weighing paper, recorded the exact mass

-Placed bottle with vinegar without a cap and the baking soda onto the scaled, the mass was recorded

-The baking soda was poured into the bottle of vinegar, after the reaction died down the mass of the product was recorded

-A burning splint was placed in the opening of the bottle and the observation was recorded

-Recorded the mass of the empty juice bottle with the cap, then poured 15mL vinegar into the juice bottle and the mass was recorded

-5g of baking soda was weighed and recorded

-Tilted the bottle of vinegar and poured the baking soda into the neck of the bottle, the cap was secured to the bottle

-The bottle then went into the upright position allowing for the baking soda to be dropped, the mass of the product was recorded

-Mass of the empty juice bottle without the cap was recorded, 15mL of vinegar was added and the mass was recorded

-5g of baking soda was weighed and recorded, as well as the mass of all the reactant (balloon, baking soda, vinegar)

-The baking soda was administered to the balloon using a scoopula, the balloon was then placed over the opening of the juice bottle (without allowing the balloon to drop any baking soda into the vinegar)

-The balloon was tipped upright in one motion, once the reaction was complete the mass of the product was recorded

Observations

Percentage Error Formula Used

Initial Mass Vs. Final Mass Graph

Discussions:

Trial 1:

The baking soda reacted with the vinegar in trial 1, causing the solution to froth and bubble. The reaction was a neutralization reaction since baking soda (sodium bicarbonate) and vinegar (acetic acid) are bases and acids. Sodium carbonate, water, and carbon dioxide were produced as a result of the process. In trial 1, the bottle’s cap was left off. As a result, the gas was able to easily exit the bottle, resulting in a different final mass measurement. We knew that gas was escaping because we could see it and smell it. The law of conservation of mass states that both reactants and products will have the same mass if the reaction is done in a closed system which was not the case in this trial. When we put our burning splint into the beaker it had gone out, signifying there was a gas that put out fires that was created.

Looking back at the hypothesis, we were in a way correct as the results of the products and reactants were very close, but not exactly perfect. This had to be the case as there was gas escaping from the top of the bottle which would mean there was mass that was unaccounted for. Human error also leads to some error in the perfection of the principle of the law of conservation. To make this trial better, an upgrade would be finding a way to have more precise measurements and to trap all the gas that was leaking to get a proper result. Measurements could have been affected by a slight shake or touch of the beakers, as the scales are very sensitive.

Trial 2:

This trial fixed the problem in the first trial. Having the cap close the bottle, we were able to contain the gas and get a better measurement. By entrapment, we had changed the environment and system the reaction took place in. In this system, all the gas within the bottle would stay there, which led to an increase in pressure as the bottle filled up with CO2. We know this because it became harder to squeeze the bottle and it let out a hiss when the cap opened. The reaction was also more intense as there was more fizzing and bubbling in the bottle. There was also no smell that we could sense which meant our cap was on tight enough to keep most of the air inside.

Analysis:

This was our most accurate trial as there was the least amount of failure points and this trial had the best way to keep most of the air inside the bottle. The percentage error was only 0.05% which means this trail verified the Law of Conservation of Mass the best out of all trials. A flaw in this trial was that there was an increase in mass on the products side, this would mean that along the way there was a human error that led to this. The reaction had also been more intense which could be due to the extra pressure in the bottle. While this trial had the lowest error percentage, there were some flaws that could be improved, like a better seal on the bottle cap.

This was our least accurate trial as the percentage error was 1.69%. We replaced the bottle cap with a balloon in this experiment, which allows all of the extra air to fill the bottle and shows us how much pressure is within. The balloon began to inflate a few seconds after the baking soda and vinegar were mixed together. The carbon dioxide produced by the process was absorbed by the balloon. On paper, this notion appears to be quite accurate because you are trapping all of the additional CO2, however in practise, this approach has significant drawbacks. The reaction was also not as prominent as the second trial.

As this was our most inaccurate trial according to the Law of Conservation of Mass, there were a few reasons that caused this. The first would be introducing the balloon. This caused two major problems, the first was that there could not be a great seal at the lip of the bottle which would cause gas to leak. The second was that, because the balloon is rubber, a lot of the baking soda stuck to the inside of the balloon and never reacted. To improve this trial I would remove the balloon as a whole and use another means to deposit the baking soda into the vinegar. The hypothesis still holds true and so does the Law of Conservation of Mass, but this trail was not the best method to verify it.

Inquiry and analysis:

Write a balanced chemical equation for the reaction in this lab.

CH3COOH(aq) + NaHCO3(s) → NaC2H3O2(aq) + H2O(l) + CO2(g)

What evidence was there that a chemical reaction occurred?

We can prove that this was a chemical reaction from a few different events that occurred. The first would be the reaction, when the two reactants mixed together, they reacted violently and created a gas which could be smelled and seen by the bubbles. We also know that Vinegar is an acid and baking soda is a base, this means that if these two substances mixed, a neutralization reaction would occur which creates a byproduct of water and a salt.

How did the final mass of the system compare with the initial mass of the system for each trial?

The final masses we got were very close to the initial mass we started with. This means that almost all of the mass was converted into a new form from the chemical reaction. Trial 2 had the smallest difference between the two masses while trial 3 had the most.

Was the law of the Conservation of Mass upheld? Explain.

While it may appear that the Law of Conservation of Mass was not completely held from our experiments, we must consider human error as well as other factors that could have influenced the final result. Overall, our results were remarkably close when we provided the optimal conditions for the least amount of gas to leave. Matter can neither be generated nor destroyed; it only takes on other forms, as it did here. None of the mass was destroyed; instead, it was lost to the atmosphere and was affected by human error. As a result, the Law of Mass Conservation has been upheld and may be demonstrated to be true.

Conclusion:

After finishing this experiment, we can conclude that the Law of Conservation of Mass is in fact true and very helpful to the world of science. This experiment did in fact support our hypothesis as when the environment of the reactions took place in changed, so did the mass of the products. We were surprised that trial 3 with that balloon had such a high failure rate compared to the open system in trial 1.

Much of the difference in masses could be blamed on human error but there were many factors that were out of our control, such as the weather, the condition of the materials, and general ruckus within the science classroom which could cause minor movements and affect the balance readings.

While considering these aspects and their effects on our experiment, we still believe that our hypothesis was correct and that the principle of the Conservation of Mass was upheld. In further research it would be interesting to push the limits of this law and see if it really does hold true for any reaction in this world or is there an expectation we don’t know of.

Bibliography

Sterner, R. (2011). The Conservation of Mass | Learn Science at Scitable . Nature.com. https://www.nature.com/scitable/knowledge/library/the-conservation-of-mass-17395478/

Study.com. (2022). The Law of Conservation of Mass: Definition, Equation & Examples . Study.com. https://study.com/academy/lesson/the-law-of-conservation-of-mass-definition-equation-examples.html#:~:text=The%20law%20of%20conservation%20of%20mass%20is%20very%20important%20to

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