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Content Benchmark P.8.A.5
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 Physical Science Matter P.8.A.1 P.8.A.2 P.8.A.3 P.8.A.4 P.8.A.5 P.8.A.6 P.8.A.7 P.8.A.8 Force and Motion Energy Content Areas Nature of Science (NOS) Life Science Earth Science Physical Science

Students know mass is conserved in physical and chemical changes.  E/S

This benchmark contains several key ideas that can be difficult for middle school students. Students must understand what physical and chemical changes are. They need to be able to differentiate between them by providing credible examples. Students must understand that as physical and chemical changes occur, matter is not created or lost and there is no change in mass between materials before or after the changes.

Figure 1. An example of the conservation of mass is shown in this stream of water that is fatter near the mouth of the faucet and skinnier lower down. This is because the water speeds up as it falls. If the cross-sectional area of the stream was equal all along its length, then the rate of flow through a lower cross-section would be greater than the rate of flow through a cross-section higher up. Because the flow is steady, the amount of water between the two cross-sections stays constant. The cross-sectional area of the stream must therefore shrink in inverse proportion to the increasing speed of the falling water. (From http://www.vias.org/physics/example_2_2_1.html)

Physical changes are those changes that materials undergo that do not alter their molecular structures and do not change their identities. They may also include energy changes. Examples include phase changes, such as ice to water and water to steam. When 20.0 grams of ice melts, there is 20.0 grams of liquid water that results from the melting. This is an easy activity to give to middle school students, which will help them understand the idea.  Similarly, physical changes can involve pounding a piece of metal into a sheet, tearing paper, or cutting a tree into logs. In these examples, there has been no change in identity or mass.  There has been a change in shape and form.  Mass is conserved and students can easily account for the pre and post changes.

To learn about conservation of mass in physical changes in solids and fluids, go to http://www.grc.nasa.gov/WWW/K-12/airplane/mass.html.

Chemical changes are particularly problematic for middle school students. Chemical changes involve changes in outer energy level electrons (ionic and covalent bonding). Explanations of chemical reactions are often abstract and students need to witness a variety of examples to fully understand that matter and mass are conserved. Simple reactions that include aqueous reactants are helpful.  Students can mass reactants before the reaction and compare them to the mass of the products after a chemical change. It is not necessary at this level that students balance chemical equations although the practice is helpful for teachers in furthering their understandings that atoms are conserved during chemical equations. Choose simple reactions for students to balance such as 2H2 + O2  à 2H20. The use of manipulatives to represent the hydrogen and oxygen atoms is helpful to convey the concept that quantities of atoms remain the same after a chemical change has occurred.

For an easy to understand tutorial about balancing chemical equations, go to http://www.chemistry.ohio-state.edu/betha/nealChemBal/

Figure 2. Reaction between hydrogen and oxygen to produce water
(From http://www.iun.edu/~cpanhd/C101
webnotes/matter-and-energy/masscons.html
)

As shown in Figure 2, students can easily develop models of hydrogen and oxygen atoms and analogously witness that in a chemical change the atoms rearrange themselves to produce water. Students do not need to worry about the type of bonding as indicated in the graphic.  Atoms touching each other are considered to be bonded.

It is important to point out to students that philosophers and scientists have long considered the concept of matter and its various properties. Democritus (460-370 BC) coined the term “atomos” when he attempted to describe the smallest form of matter.  John Dalton furthered this idea with the development of the first atomic theory in the 18th century. Both recognized that the atom is the smallest unit of matter that is indivisible. This is the concept which leads to the development of the Law of Conservation of Mass in a chemical reaction.  The mass of the reactants is always equal to the mass of the products in a normal chemical reaction.

An excellent discussion of the development of atomic theory and it relationship to the conservation of mass is found at
http://www.visionlearning.com/library/module_viewer.php?mid=49.

To reinforce the idea that gases have mass, students should be given the opportunity to experiment with reactions in which gases are produced. If students place an alka-seltzer tablet in water, they will observe a gas being produced.  Weighing the water and the alka-seltzer tablet before and after the reaction, will allow students to see that the masses change because the gas is lost to the atmosphere.  Repeating the reaction in a Ziploc bag will demonstrate that matter was conserved as the masses are conserved and should naturally lead to a conversation about gases having mass.

Figure 3. Schematic of a simple experiment demonstrating the conservation of mass
(From http://www.tea.state.tx.us/student.assessment/
)

For a more detailed explanation of chemical and physical changes including a short video, go to http://edcommunity.apple.com/ali/story.php?itemID=196. The purpose of the project is for students to learn about the properties of matter, including phase changes in matter, physical, and chemical properties of matter, and physical and chemical change. The students demonstrate their understanding by creating a movie that can be shared with others.

Content Benchmark P.8.A.5

Students know mass is conserved in physical and chemical changes.  E/S

Common misconceptions associated with this benchmark

1. Students incorrectly think that gases are not matter because most gases are invisible. Similarly, students believe that gases do not have mass.

Since their experiences with gases are limited, students are often confused by the characteristics and the properties of gases. One of the major misconceptions is that gases have no mass. Teachers can assist students in confronting this misconception by allowing them to perform some simple experiments in which they can mass a particular volume of gas. One good example is the sublimation of dry ice. Providing students with a small amount of dry ice that they can mass and then place in a Ziploc bag to observe its sublimation will allow them to see a solid actually sublime. They can observe the phase change, witness that no chemical change has occurred and then re-mass the substance to see that its mass has remained constant will help avoid this common misconception.

Annenberg’s “A Private Universe” http://www.learner.org/resources/series26.html will assist the teacher in understanding the difficulties that middle school students face when trying to understand properties of gases.

2. Students are confused about the conservation of particles during a chemical change. Also, Students frequently disregard particle conservation and orderliness when describing physical changes.

Students have limited experience with chemical changes and often believe that substances mysteriously appear and disappear in chemical reactions. Some of these misconceptions are media induced. Having students develop models of chemical reactions before a chemical change and after a chemical change will assist them in developing more sophisticated ideas regarding the conservation of matter.

One example of a model that students can build is exemplified in the table below.

 2H2 + O2 2H2O + 2 * 2.02g + 32.00g = 2 * 18.02g

Figure 4. A model of a chemical reaction forming water.
(From http://www.visionlearning.com/library/module_viewer.php?mid=56)

To get a listing of this misconception and other physical science misconceptions, go to http://homepage.mac.com/vtalsma/syllabi/2943/handouts/misconcept.html#physical.

3. Students incorrectly think that chemical and nuclear reactions are the same.

Students may inquire about nuclear reactions and the teacher needs to be able to differentiate between a nuclear change and a chemical change. Nuclear changes involve changes in the nucleus of an atom and can result in changes in mass. Chemical changes involve only outer energy level electrons. It might be useful to point out to students that nuclear fusion occurs in the Sun producing helium from the fusion of hydrogen nuclei. The change does not involve electrons, but rather the changes occur in the nuclei with the release of large amounts of energy.

Figure 5. A cut-away of the solar interior showing the
core, radiative zone and convection zone.
(From http://sunearthday.nasa.gov/2007/locations/ttt_solarenergy.php)

Energy is an important by-product of nuclear fusion as witnessed by the power of the Sun. The nuclear process is demonstrated by the following reaction diagram.

Figure 6. The Proton-Proton Cycle, protons colliding
to produce a deuterium nucleus and energy.
(From http://sunearthday.nasa.gov/2007/locations/ttt_solarenergy.php)

In a chemical reaction, no such changes in the nucleus are observed. Recall the reaction for the formation of water:

 2H2 + O2 2H2O + 2 * 2.02g + 32.00g = 2 * 18.02g

Figure 7. A model of a chemical reaction forming water.
(From http://www.visionlearning.com/library/module_viewer.php?mid=56)

The atoms combine in simple whole number ratios that do not involve the nucleus but rather the outer valence electrons.

4. Students incorrectly think that chemical changes are determined by features of the change.

For example, if a piece of paper is ignited within a closed container, students observing the smoke will believe the flask should weigh more after the paper combusts. Teachers can point this misconception out to students by weighing materials before and after the change.

and, http://www.deakin.edu.au/arts-ed/education/sci-enviro-ed/early_years/physical.php.

Content Benchmark P.8.A.5

Students know mass is conserved in physical and chemical changes.  E/S

Sample Test Questions

1st Item Specification: Identify that the total mass remains the same in a chemical change (i.e., the number and type of atoms in the reactants equals the number and type of atoms in the products).

Depth of Knowledge Level 1

1. Examine the following table and use it to answer the following question.

 2H2 + O2 2H2O + 2 * 2.02g + 32.00g = ? g
What is the total mass of water formed?
1. 2.02 g
2. 32.0 g
3. 36.0 g
4. 18.0 g
1. In chemical and physical changes,
1. mass is gained, but energy remains the same after the changes occur.
2. both mass and energy remain the same after the changes occur.
3. both mass and energy are lost after the changes occur.
4. mass is lost, but energy remains the same after the changes occur.
1. Which of the following statements is true of a chemical reaction?
1. Mass is converted into energy.
2. Energy is converted into mass.
3. Mass and energy are conserved.
4. Mass and energy are not involved.
1. Examine the following reaction:

Ca + Cl2 → CaCl2

According to the Law of Conservation of Mass,

1. there should be equal numbers of atoms on both sides of the equation.
2. the mass of the products should be less due to bonding changes.
3. the mass of the products increases because energy changes to mass.
4. the numbers of atoms should be decreased due to nuclear changes.
1. According to the Law of Conservation of Mass the number of iron atoms needed to complete the following reaction is

___Fe  +  3O2 →  2Fe2O3

1. 1
2. 2
3. 3
4. 4

Depth of Knowledge Level 2

1. A student dissolves 5 grams of salt in 20 grams of water.  The mass of the resulting solution is
1. less than 25 grams because some of the salt disappears.
2. less than 25 grams because water weighs less than salt.
3. equal to 25 grams because the mass includes all of the salt and all of the water.
4. more than 25 grams because some of the salt weighs more when it dissolves in water.
1. A student masses a quantity of vinegar and baking soda and places them into a massed Ziploc® bag.  The bag begins to expand as the vinegar and baking soda react vigorously with each other.  When the reaction is complete, the student re-masses the bag. Which of the following statements is true?
1. The mass of the bag and its contents is the same as the original mass of the substances.
2. The mass of the bag and its contents is less than the original mass of the substances.
3. The mass of the bag and its contents is more than the original mass of the substances.
4. The mass cannot be determined because energy changes were not considered.
1. A student measures the mass a piece of metal and places it in a dish at his desk.  After a week, he observes that the metal has changed appearance. He re-masses the metal and notes that its mass has increased. What is the correct explanation for his observation?
1. Time causes the mass of objects to change.
2. Mass does not change so the metal cannot be the same metal.
3. A reaction with the air occurred causing a new substance to form.
4. The balance contained an error and should be recalibrated.
1. Two chemicals, A and B, react to form compounds C and D. If 12 grams of A react completely with 5 grams of B, and 7 grams of D are formed, then how many grams of C are formed?

A + B → C + D

1. 5 grams
2. 7 grams
3. 10 grams
4. 17 grams
1. Given the balanced equation

6CO2(s)  +  6H2O (aq) → C6H12O6 (aq)  +  6O2(g)

How many atoms of oxygen are reacting?

1. 6
2. 7
3. 12
4. 18

2nd Item Specification: Know matter is conserved in a physical change.

Depth of Knowledge Level 1

1. When a gas condenses to the liquid state, its mass
1. changes because the phase has changed.
2. remains the same even though the phase has changed.
3. is lighter because gases weigh less than liquids.
4. is heavier because liquids weigh more than gases.
1. In the figures below, molten gold is solidified. Use the figures to answer the following question.

Which of the following describes what is happening as the molten gold is solidified?

1. Atoms are lost during the solidification process.
2. Atoms are lost during the melting phase.
3. Atoms are gained in phases changes.
4. Atoms remain the same during phase change
1. The figure below shows a piece of metal being pounded by a hammer. Use the figure to answer the following question.

When a piece of metal is being pounded by a hammer,
the impact causes

1. atoms to be smashed into smaller pieces.
2. the metal to change its chemical formula.
3. no change in the metal’s chemical properties.
4. energy changes in the nucleus of the metal’s atoms
1. A student burns a candle in the laboratory and makes several observations. Which of her conclusions is correct?
1. The mass of the candle does not include the gases that escaped.
2. The candle is composed of the wax left over from the burning candle.
3. The candle’s behavior is affected by the type of wick it has.
4. The mass of the remainder of the candle is heavier because it is denser.
1. A student masses three equal amounts of salt. She then dissolves them in different amounts of water. She then evaporates the water and re-masses each sample of salt. All the amounts will be
1. different because different amounts of water were used.
2. different because of density differences in the substances.
3. the same because different amounts of water were used.
4. the same because the substances did not physically change.

Depth of Knowledge Level 2

1. A student is studying the phase change of ice (solid water) to liquid water to steam (gaseous water). The student correctly predicts that
1. the total mass of ice changing to liquid phase is the same because mass is conserved.
2. the total mass of ice will be less in the water phase because water takes up less volume than ice.
3. the total mass of water converting to steam will be less because gases do not contribute to the mass of a substance.
4. the mass of the ice will be more than the mass of steam because solids are heavier.
1. The melting of wax is a physical change, yet the burning of wax is a chemical change. What is the primary difference between the chemical change and physical change of wax in a burning candle?
1. The burning of wax forms new compounds, while the melting of wax does not.
2. A higher temperature is needed to burn wax than to melt wax.
3. Melted wax can be separated into other substances, while solid wax cannot.
4. Melted wax is a different phase of matter than solid wax.
1. A student is trying to distinguish between physical and chemical changes. He states that in physical changes, mass is not conserved. Which of the following would help correct his thinking?
1. Tear 5.0 grams of paper and examine the ripped edges.
2. Take 5.0 grams of ice melt it and remass it.
3. Take 5.0 grams of charcoal and burn it.
4. Take 5.0 grams of sugar and dissolve it in water.
1. A student takes a small piece of dry ice and notices that it is not visible (sublimes) in a few minutes. She concludes that dry ice does not contain atoms. Which of the following might correct her thinking?
1. Take more dry ice, mass it and then observe it sublime.
2. Take the dry ice, place it in a bag and mass it before and after it sublimes.
3. Take the dry ice, mass it, and then mix it with water to see if it reacts.
4. Take the dry ice, mass it, and then time how long it takes to sublime.

Constructed Response P.8.A.5

1. A student takes a small piece of dry ice, places it in a Ziploc bag, and masses it. After a few minutes she observes that it is not visible.  She re-masses the bag and finds that the quantity has not changed. How would you explain her observations?

Content Benchmark P.8.A.5

Students know mass is conserved in physical and chemical changes.  E/S

1. C, DOK Level 1
2. B, DOK Level 1
3. C, DOK Level 1
4. A, DOK Level 1
5. D, DOK Level 1
6. C, DOK Level 2
7. A, DOK Level 2
8. C, DOK Level 2
9. C, DOK Level 2
10. D, DOK Level 2
11. B, DOK Level 1
12. D, DOK Level 1
13. C, DOK Level 1
14. A, DOK Level 1
15. D, DOK Level 1
16. A, DOK Level 2
17. A, DOK Level 2
18. B, DOK Level 2
19. B, DOK Level 2

Constructed Response 3-point Answers and Score Rubrics:

 3 points Response addresses all parts of the question clearly and correctly. Student response indicates that dry ice is a solid and sublimes (or answer similar), only a physical change has occurred, gases have mass and occupy volume, and mass is conserved in physical changes. 2 points Response addresses all parts of the question and includes only minor errors. 1 point Response does not address all parts of the question. 0 point Response is totally incorrect or no response provided.

Content Benchmark P.8.A.5

Students know mass is conserved in physical and chemical changes.  E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Science Help Online Chemistry, Physical and Chemical Properties and Changes

Developed by Fordam Prepatory School, this site contains a further explanation of chemical and physical changes, including worksheets, assessments, and answers. Some of the activities may be more appropriate for advanced students; however, parts of the worksheets are completely appropriate for the “meets” designation by the Nevada State Department of Education.

To access these activities, go to
http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson15.htm

2. Physical or Chemical Change?

This activity was created by a Quia Web subscriber and contains an online quiz regarding chemical and physical changes. It can be used as a pre or post quiz on physical and chemical change. The site does not provide feedback for students.

To access these activities, go to
http://www.quia.com/quiz/303980.html

3. Beacon Lesson Plan Library, Conservation of Mass

This site provides a well-designed lesson focused on the Law of Conservation of Mass. Students observe a chemical reaction, determine that a gas has mass, and confirm the law of conservation of mass and energy. After completing the lab activity, a multiple choice assessment is provided for the teacher.

To access these activities, go to
http://www.beaconlearningcenter.com/Lessons/493.htm

4. Conservation of Matter and Balancing Chemical Equations

Developed by the University of Virginia, Physics Department, this website contains a lesson unit on the conservation of mass and includes several equations for students to balance. There is also an assessment with answers provided. One note for the teacher is that although the Nevada State Science Standards do not explicitly state that students should be able to balance equations, they can accomplish equation balancing using manipulatives or by drawing pictures which model the equation.

To access these activities, go to