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Antoine Lavoisier's discovery of the Law of Conservation of Mass is the basis for much of what is taught in Chem-

istry. It is this law that requires students to balance chemical equations and understand what it means that mass is

not lost. Students have a difficult time understanding this because many times this is just told to them without

proof or the experiment done in class to prove it fails in its proof. This MEL hopes to give students a hands on

experience in seeing and proving the law of conservation of mass and how it applies to balancing chemical equa-

tions.

This issue of Science Dissected provides an instructional resource for teachers to present students with the oppor-

tunity to examine several pieces of evidence compiled about the law of

Science DissectedScience DissectedScience DissectedScience Dissected

A C o n t e n t S e c o n d a r y S c i e n c e N e w s l e t t e r f r o m t h e A C o n t e n t S e c o n d a r y S c i e n c e N e w s l e t t e r f r o m t h e A C o n t e n t S e c o n d a r y S c i e n c e N e w s l e t t e r f r o m t h e A C o n t e n t S e c o n d a r y S c i e n c e N e w s l e t t e r f r o m t h e

S o u t h e r n N e v a d a R e g i o n a l P r o f e s s i o n a l D e v e l o p m e n t P r o g r a mS o u t h e r n N e v a d a R e g i o n a l P r o f e s s i o n a l D e v e l o p m e n t P r o g r a mS o u t h e r n N e v a d a R e g i o n a l P r o f e s s i o n a l D e v e l o p m e n t P r o g r a mS o u t h e r n N e v a d a R e g i o n a l P r o f e s s i o n a l D e v e l o p m e n t P r o g r a m

Archived Issues of Science Dissected, http://www.rpdp.net/link.news.php?type=sciencedis. Instructional Resource result-

ing from Plausibility, It’s All About Connecting the Models Workshop co-sponsored by CPDD and SNRPDP

Science March 6, 2012 Written by: Sarah MacNab

Conservation of Mass Model-Evidence Link Diagram (MEL)

Model B: Students conducted an experiment using sodium hydroxide and aluminum foil. Their mass after the reaction was the same as the mass before. The students state this proves the law of conservation of mass.

Once students have completed page 2, they can then engage in collaborative argumentation as they compare their

links and explanations with that of their peers. Students should be given the opportunity to revise the link weighting

during the collaborative argumentation exercise. If time permits, have students reflect on their understanding of the

conservation of mass and create questions that they might explore in the future.

Model A: Students conducted an experiment using sodium hydroxide and aluminum foil. Their mass after the reaction was less then the mass before. The students state this disproves the law of conservation of mass.

The following is a suggestion for us-

ing this MEL with students:

1. Hand out the Law of Conservation of

Mass Model Evidence Link Diagram (pg

1). Instruct students to read the directions,

descriptions of Model A and Model B,

and the five evidence texts presented.

2. Handout the five evidence text pages (pgs

3-18).

3. Instruct students to carefully review the

Evidence #1 text page (pg 3), then con-

struct two lines from Evidence #1; one to

Model A and one to Model B. Remind

students that the shape of the arrow they

draw indicates their plausibility judgment

(potential truthfulness) connection to the

model.

4. Repeat for Evidence #2-5 (pgs 5-18).

5. Handout page 2 for the students to criti-

cally evaluate their links and construct

understanding.

Evidence #1: Complete the Lab – The First Law of Chemistry – Conservation of Mass . Compare results by adding your results to the class Google Doc. What does the data prove? What could be possible sources of error? Evidence #2: The Law of Conservation of Mass holds true because naturally occurring elements are very stable at the conditions found on the surface of the Earth. Evidence #3: The pictures of the reactions are telling us what? Count the different reac-tants and products. Are the number and type of atoms equal on both sides? Evidence #4: Compete Law of Conservation of Mass –Experiment 3 and compare results by adding your results to the class Google Doc. Which model does the data prove? Evidence #5: Many experiments and balanced chemical equations show us… Complete the Conservation of Mass and Balancing Chemical Equations Experiment. What did it show you?

Model B - Students conducted an experiment using sodium

hydroxide and aluminum foil. Their mass after the reaction

was the same as the mass before. The students state this proves the law of conservation

of mass.

Model A – Students conducted an experiment using sodium

hydroxide and aluminum foil. Their mass after the reaction was less then the mass before.

The students state this disproves the law of

conservation of mass.

Evidence #1Complete the Lab – The First Law

of Chemistry – Conservation of

Mass . Compare results by adding your results to the class Google Doc. What does the data prove? What could be possible sources of error?

Evidence #2The Law of Conservation of

Mass holds true because

naturally occurring elements are

very stable at the conditions

found on the surface of the

Earth.

Evidence #4Compete Law of Conservation of Mass –Experiment 3 and compare results by adding your results to

the class Google Doc. Which model does the data prove?

Name:_______________________________________ ___________________ Period:_______________

Directions: draw two arrows from each evidence box. One to each model. You will draw a total of 10 arrows.

Key:

The evidence supports the model

The evidence STRONGLY supports the model

The evidence contradicts the model (shows its wrong)

The evidence has nothing to do with the model×

1

Standard: P.12.A.7

Evidence #3The pictures of the reactions are

telling us what? Count the different

reactants and products. Are the

number and type of atoms equal on

both sides?

Evidence #5Many experiments and balanced

chemical equations show us…

Complete the Conservation of

Mass and Balancing Chemical

Equations Experiment.

Provide a reason for three of the arrows you have drawn. Write your reasons for the three most interesting or important arrows.

A. Write the number of the evidence you are writing about.B. Circle the appropriate descriptor (strongly supports | supports | contradicts | has nothing to do with).C. Write the letter of the model you are writing about.D. Then write your reason.

1. Evidence # ____ strongly supports | supports | contradicts | has nothing to do with Model _____ because:



2

4. Circle the plausibility of each model. [Make two circles. One for each model.]

Greatly implausible(or even impossible)

Highly Plausible

Model A 1 2 3 4 5 6 7 8 9 10

Model B 1 2 3 4 5 6 7 8 9 10

5. Circle the model which you think is correct. [Only circle one choice below.]

Very certain that Model A is correct

Somewhat certain that Model A is correct

Uncertain if Model A or B is correct

Somewhat certain that Model B is correct

Very certain that Model B is correct

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Evidence #1: Complete the Lab – The First Law of Chemistry –

Conservation of Mass . Compare results by adding your results to the

class Google Doc. What does the data prove? What could be possible

sources of error?

LAB – First Law of Chemistry – Conservation of Mass Discovered by Lavoisier

Name: ___________________________ Lab Station / Group # ________ Period: ________ Date: ________________ Purpose: Observe both endothermic and exothermic reactions. Mix the reactants (each in their own

corner of a plastic bag) of this chemical reaction together with a diluted phenol red solution. Observe the reaction and record everything you see. Practice writing a procedure. Learn the “First Law of Chemistry” by first hand experience.

Materials:

chemicals: sodium hydrogen carbonate (NaHCO3) 9 g ± 0.5 g anhydrous calcium chloride (CaCl2 ) 7 g ± 0.5 g diluted phenol red solution (1:10 dilution with H2O) 8.5 mL ± 1 mL (red if in base - yellow if in acid) equipment: centigram balance 1 qt Ziploc plastic bag (reaction bag) 10 mL graduated cylinder masking tape (for labeling things) filter paper goggles

Chemical reactions being observed: Mimics you stomach making acid 2 NaHCO3 (aq) + CaCl2 (aq) + H2O (l) ----> CaCO3 (s) + 2 NaCl (aq) + H3O

+ (aq) (exo)

Mimics you taking sodium bicarbonate for excess stomcach acid H3O

+ (aq) + NaHCO3 (aq) ----> CO2 (g) + H2O (l) + Na+

(aq) (endo) NOTE: Share responsibilities within your group. Everyone should have a job. Use filter

paper on the pan to weigh out your dry chemicals. Never put chemicals directly on the chrome pan of the balance.

Procedure: You will write your own procedure. The data table below may be helpful. Your procedure must include

step-by-step directions on how you will weigh out NaHCO3 with CaCO3 and place them in opposite ends of a plastic Ziploc bag . 10 mL of diluted phenol red must be poured into the bag to mix your chemicals so that the bag doesn’t lose any gas that is produced. You will have to consider safety precautions for what you will do if too much CO2 (g) is formed for the bag to hold.

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Observations: You set up your own observation section that must include: 1. temperature – as felt with your hands at each end of the bag Exothermic reactions produce heat. Endothermic reactions get colder (suck up heat). 2. gas formation – where & approximately how much 3. change or lack of change of mass for the bag with everything inside, before and after the

reaction. 4. color and texture of chemicals (dry & liquid) before and after the reaction 5. every change that indicated a chemical reaction occurred at any stage of the mixing of the

chemicals with the phenol red solution

DATA TABLE

Items masses (to 3 decimals)

volumes (to 1 – 2 decimals)

plastic bag – grams

filter paper – grams NaHCO3 9 g ± 0.5 g

CaCl2 7 g ± 0.5 g

10 ml grad cylinder -

grams

diluted phenol red 8.5 mL

± 1 mL - mass and vol.

mass of plastic bag with all

chemicals (before

readction starts)

mass of plastic bag with all

chemicals (5 min after

reaction starts)

From: http://www.mrwiggersci.com/chemold/Labs/lab_first-law-chem.htm

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Evidence #2: The Law of Conservation of Mass holds true because

naturally occurring elements are very stable at the conditions found

on the surface of the Earth.

The Conservation of Mass By: Robert W. Sterner (Department of Ecology, Evolution, and Behavior, University of Minnesota), Gaston E. Small (Department of Ecology, Evolution, and Behavior, University of Minnesota) & James M. Hood (Department of Ecology, Evolution, and Behavior, University of Minnesota) © 2011 Nature Education

Citation: Sterner, R. W., Small, G. E. & Hood, J. M. (2011) The Conservation of Mass. Nature Education Knowledge 2(1):11

The Law of Conservation of Mass The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction. If we account for all reactants and products in a chemical reaction, the total mass will be the same at any point in time in any closed system. Lavoisier's finding laid the foundation for modern chemistry and revolutionized science. The Law of Conservation of Mass holds true because naturally occurring elements are very stable at the conditions found on the surface of the Earth. Most elements come from fusion reactions found only in stars or supernovae. Therefore, in the everyday world of Earth, from the peak of the highest mountain to the depths of the deepest ocean, atoms are not converted to other elements during chemical reactions. Because of this, individual atoms that make up living and nonliving matter are very old and each atom has a history. An individual atom of a biologically important element, such as carbon, may have spent 65 million years buried as coal before being burned in a power plant, followed by two decades in Earth's atmosphere before being dissolved in the ocean, and then taken up by an algal cell that was consumed by

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a copepod before being respired and again entering Earth's atmosphere (Figure 1). The atom itself is neither created nor destroyed but cycles among chemical compounds. Ecologists can apply the law of conservation of mass to the analysis of elemental cycles by conducting a mass balance. These analyses are as important to the progress of ecology as Lavoisier's findings were to chemistry.

Figure 1: Hypothetical pathway of a carbon atom through an ecosystem Because elements are neither created nor destroyed under normal circumstances, individual atoms that compose living organisms have long histories as they cycle through the biosphere. In this depiction, a carbon atom moves from coal buried beneath the Earth's surface to a power plant and into the atmosphere. It eventually dissolves in water and is taken up by an algal cell, where it is then consumed by a copepod. Labels also indicate the length of time that the atom spends in each compartment.

© 2011 Nature Education All rights reserved.

Life and the Law of Conservation of Mass

Figure 2: Ecosystems are represented as a network of various biotic and abiotic compartments, connected through the exchange of materials and energy. Every compartment has inputs and outputs.

© 2011 Nature Education All rights reserved. Life involves obtaining, utilizing, and disposing of elements. The biomolecules that are the building blocks of life (proteins, lipids, carbohydrates, and nucleic acids) are composed of a relatively small subset

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of the hundred or so naturally occurring elements. Living organisms are primarily made of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. And each of these important elements cycle through the Earth system. Ecosystems can be thought of as a battleground for these elements, in which species that are more efficient competitors can often exclude inferior competitors. Though most ecosystems contain so many individual reactions, it would be impossible to identify them all, each of these reactions must obey the Law of Conservation of Mass — the entire ecosystem must also follow this same constraint. Though no real ecosystem is a truly closed system, we use the same conservation law by accounting for all inputs and all outputs. Scientists conceptualize ecosystems as a set of compartments (Figure 2) that are connected by flows of material and energy. Any compartment could represent a biotic or abiotic component: a fish, a school of fish, a forest, or a pool of carbon. Because of mass balance, over time the amount of any element in any one of these compartments could hold steady (if inputs = outputs), increase (if inputs > outputs), or decrease (if inputs < outputs). For example, early successional forests gain biomass as trees grow and thus act as a carbon sink (Figure 3). In mature forests, the amount of carbon taken up through photosynthesis may equal the amount of carbon respired by the forest ecosystem, so there is no net change in stored carbon over time. When a forest is cut (and especially if trees are burned to clear land for agriculture), this stored carbon reenters the atmosphere as CO2. Mass balance ensures that the carbon formerly locked up in biomass must go somewhere; it must reenter some other compartment of some ecosystem. Mass balance properties can be applied over many scales of organization, including the individual organism, the watershed, or even a whole city (Figure 4).

Article From: http://www.nature.com/scitable/knowledge/library/the-conservation-of-mass-17395478

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Evidence #3: The pictures of the reactions are telling us what?

Count the different reactants and products. Are the number and

type of atoms equal on both sides?

Image from: 2009rt8scimariam.wordpress.com

Reactants Products

Quantity Hydrogen: Quantity Hydrogen:

Quantity Oxygen: Quantity Oxygen:

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Image from : s-o.k12.ia.us

Reactants Products

Quantity Carbon: Quantity Carbon:


Quantity Hydrogen : Quantity Hydrogen :

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Image from: http://www.personal.kent.edu/~cearley/gen50/balance/balance.htm

Reactants Products

Quantity Carbon: Quantity Carbon:


Quantity Hydrogen : Quantity Hydrogen

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Here are pictures of the reactions:

Reaction 1: Mix lead nitrate and potassium iodide solutions

Reaction 2: Mix copper sulfate and sodium hydroxide solutions

Reaction 3: Mix barium chloride and sodium sulfate solutions.

Reaction Picture of reactants Picture of mixing Picture of products

lead nitrate and potassium iodide solutions

copper sulfate and sodium hydroxide solutions

barium chloride and sodium sulfate solutions.

Image from: http://www.saskschools.ca/curr_content/science10/unitb/lwmsrxns.html

Note the Masses before and after reactions

What do you observe about the mass?

Is this a closed or open system?

Which system is better for observing the law of conservation of mass?

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Evidence #4: Compete Law of Conservation of Mass –Experiment 3 and

compare results by adding your results to the class Google Doc. Which

model does the data prove?

Law of Conservation of Mass - Experiment 3

The experiment will explore whether matter is created or destroyed during a chemical reaction.

Materials Substitutions

solutions of NaOH, CuSO4, NH4OH, and Na2CO3

solutions made with Drano, Bluestone algaecide, ammonia, and washing soda

4 graduated cylinders 4-2 oz plastic cups

3 150-mL beakers 3-5 oz plastic cups

balance

Procedure 1. Label the four graduated cylinders (or 2 oz cups) to contain the solutions (one each for

NaOH, CuSO4, NH3 (aq), and Na2CO3). 2. Use a graduated cylinder to measure about 60 mL (2 oz) of the NaOH solution. Use a

second graduated cylinder to measure about 60 mL (2 oz) of the CuSO4 solution and pour it into a 150-mL beaker (or 5 oz cup).

3. Carefully place the two solutions (in their containers) on the balance. Weigh the solutions and their containers together and record their combined weight.

4. Pour the NaOH solution into the container with the CuSO4 solution. Allow the solutions to mix. Describe what happens.

5. Weigh both containers and the mixture again. Record the new weight. Did the weight change?

6. Repeat the process in steps # 2 and #3 above, first substituting NH3 (aq.) for the NaOH solution, then substituting Na2CO3 for the NaOH solution. In each case measure and record the masses as described in steps #3 and #5 above.

Data and Observations 1. Total weight of NaOH and CuSO4: Before __________g After _______g 2. Total weight of NH3 (aq) and CuSO4: Before __________g After _______g 3. Total weight of Na2CO3 and CuSO4: Before __________g After _______g Complete the following equations: 4. NaOH + CuSO4 ----->_________________________________ 5. NH3 (aq)+ CuSO4 ------->_____________________________ 6. Na2CO3 + CuSO4 ------->____________________________ Extensions The substances chosen for this lab are common and easy to find. You may want to repeat this lab with solutions of Fe(NO3)2 or Zn(NO3)2 solutions with Na2CO3. or NaOH. Note that NEITHER

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iron(II) or zinc carbonates or hydroxides are as insoluble as the copper(II) analog. While barium and lead salts have frequently been used in this type experiment, the problems associated with disposing of these materials suggests NOT USING either of these salts in experiments. Questions 1. What is the insoluble solid that is produced? Use a solubility chart to predict the identity of the insoluble product. 2. Use the periodic table to prove that total formula mass is conserved. Why is it important to balance a chemical reaction? Teacher's Notes This experiment verifies the Law of Conservation of Matter: Matter is neither created or destroyed as a result of chemical changes but may be changed in form. The balanced equations are as follows: 4. 2NaOH (aq) + CuSO4 (aq) -----> Na2SO4 (aq) + Cu(OH)2 (s) 5. 4NH3 (aq) + CuSO4 (aq) -------> Cu(NH3)4SO4 (s) 6. Na2CO3 (aq) + CuSO4 (aq) -------> Na2SO4 (aq) + CuCO3 (s) The insoluble product that is formed is called a precipitate. Solubility Tables can help students predict which product will be insoluble (form a precipitate) For additional ideas on this concept, see Experiment #2 and the Teacher's Notes. Solution Preparation The sodium hydroxide can be obtained from Drano™ or Red Devil™ Lye. If you use Drano, the solution does not need to be very concentrated but you would want to filter the aluminum filings that are mixed in with the pellets of NaOH. Lye is CAUSTIC so wear gloves and wash all surfaces anyone might touch. Copper (II) sulfate can be purchased at a good hardware or swimming pool supply store as an algaecide (Bluestone) or root eater. Aqueous ammonia (formerly called ammonium hydroxide) is nothing more than household ammonia, and can be used straight out of the bottle from the grocery store. Finally, the sodium carbonate can be purchased at the grocery store as washing soda (Arm and Hammer) and can be mixed with water to form a solution. 0.1 M solutions can be prepared by dissolving the following masses of solid into enough water to make 1-L of solution:

Copper sulfate Sodium hydroxide Sodium carbonate

25g 4 g 10.6 g

Safety Precautions As mentioned in the solutions preparations section, sodium hydroxide is CAUSTIC and should be handled carefully. Students should wear gloves. The base will feel slippery on the skin and should be washed immediately. Copper solutions can cause eye infections, so students should wash their hands after handling these substances, too. Disposal

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All solids should be placed in solid-waste containers. Most solutions can be poured down the sink. Check your local municipal water regulations concerning copper sulfate, as some water regulators restrict the concentration of copper (II) ions that can be poured down drains.

This work by The Science House is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Tags: Chemistry Middle School High School Investigation

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Evidence #5: Many experiments and balanced chemical equations

show us… Complete the Conservation of Mass and Balancing

Chemical Equations Experiment.

University of Virginia Physics Department

Conservation of Matter and Balancing Chemical Equations

A Physical Science Activity

Materials

Solution of NaOH Solution of CuSO4 Solution of NH4OH Solution of Zn(NO3)2 Four 3oz. plastic cups Three 5 oz. plastic cups Balance Gaduated cylinder

Procedure

1. Measure 60 mL of NaOH solution in a graduated cylinder and then pour into a small (3 oz) clean plastic cup.

2. Rinse the graduated cylinder completely before making the next measurement.

3. Measure 60 mL of CuSO4 solution in the graduated cylinder and then pour it into a clean 5 oz cup.

4. Carefully place the two solutions on the balance, making sure the solutions do not mix. Mass the solutions and the cups together and record the combined mass.

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5. Pour the NaOH into the 5 oz cup with the CuSO4 solution. Allow the solutions to mix. Record your observations.

6. Mass both cups and the mixture again. Record the new mass. By how much did the mass change?

7. Repeat the process in steps 1-4 above for the combinations listed in the data section below. Do not allow the solutions to mix before taking the initial mass.

Data Sheet

Reaction Mass (g) Before Mass (g) After Observations

NaOH and CuSO4

NH4OH and CuSO4

NH4OH and Zn(NO3)2

Complete the following equations and balance:

1. ___ NaOH + ___ CuSO4 -----> _____________________________________________

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2. ___ NH4OH + ___ CuSO4 -----> ____________________________________________

3. ___ NH4OH + ___ Zn(NO3)2 -----> __________________________________________

Assessment

(Please answer in complete sentences):

1. What is the insoluble solid that is produced generally called?

_____________________________________________________________________

2. Use the provided solubility chart to predict the identity of the insoluble products.

1. ______________________________

2. ______________________________

3. ______________________________

3. Why is it important to balance a chemical reaction?

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_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

4. Balance the following equations:

___ MnO2 + ___ HCl -----> ___ MnCl2 + ___ H2O + ___Cl2

___ Pb(NO3)2 + ___ K2CrO4 -----> ___PbCrO4 + ___KNO3

___ CO + ___ Fe2O3 -----> ___ Fe + ___ CO2

___ Zn(OH)2 + ___ H3PO4 -----> ___ Zn3(PO4)2 + ___ H2O

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