MS-PS1-1 Develop models to describe the atomic composition of simple molecules and extended structures.
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MS-PS1-5. Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
1. Unpacking Core Ideas
Component -- PS1.B. Chemical Reaction
Element:
● Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and those new substances have different properties from those of the reactants.
Elaboration of Ideas
Macroscopic level:
○ A chemical reaction is the change of a substance(s) into a new one that has a different
chemical identity. It is usually observed through physical effects, such as the formation of precipitate or gas, a color change, or heat transfer. However, the confirmation of chemical change can only be validated by analysis of the properties of the products.
1.
When substances react chemically, one or more new substances are formed.
2.
New substances formed are the products of a chemical reaction.
3.
It is possible for a single substance to undergo a chemical reaction.
4.
Liquids, solids, or gases can be reactants or products in chemical reactions.
○ When substances undergo chemical reactions, the total mass of all the substances will always remain the same.
1.
The total mass of the substances before and after they interact is equal. In other words, the mass is conserved.
Atomic level:
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○ A chemical reaction is a process whereby the atoms that make up the molecules of the original substances rearrange into new molecules, so that the types and number of atoms do not change.
1.
New substance are made of the same kinds of atoms as the original substances
2.
The number of atoms before and after the substances interact is equal.
Boundary
1.
Students are expected to know that the original substances in a chemical reaction are called reactants and the resulting substances are called products but they will not be assessed on these definitions.
2.
Students are not expected to know the term “bond” or how chemical bonds are formed or broken during chemical reactions.
3.
Students are not expected to know the difference between “weight” and
“mass.”
Prior-Knowledge
Students developed these ideas in 5th Grade:
5-PS1-4 Conduct an investigation to determine whether the mixing of two or more substances results in new substances.
Student Challenges
1.
Students understood that chemical reactions involve liquids only and that a reaction always happens when two liquids combine.
2.
Students thought that the total mass decreases during a chemical reaction when a gas is produced (Ozmen et al, 2003), or a solid dissolved in a liquid (Stavy, 1990; Ozmen et al,
2003).
3.
Students thought that the total mass increases during a precipitation reaction
(Baker et al, 1999; Ozmen et al, 2003).
2. Unpacking Practice
Developing and using models
1.
Develop or modify a model (based on evidence) to match what happens if a variable or component of a system is changed.
2.
Develop and/or revise a model to show the relationships among variables, including those that are not observable but predict observable phenomena.
3.
Develop and/or use a model to predict and/or describe phenomena.
Scientific model: a scientific model is an abstract, simplified, representation of a system or phenomena that makes its central features explicit and visible and can be used to generate explanations and
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predictions. It includes diagrams, physical replicas, mathematical representations analogies, and computer simulations. Our model framework includes three components: component, relationship, and connection.
● Component: Model includes identification and specification of appropriate and necessary components, including both visible and invisible.
● Relationship: Model includes representations or descriptions indicating how various components within the model are related and interact with each other.
● Connection: Model is used to explain or predict phenomena or specific aspects of phenomena.
Prior-Knowledge
In Grades 3-5, building and revising simple models and using models to represent events and design solutions.
1.
Identify limitations of models.
2.
Collaboratively develop and/or revise a model based on evidence that shows the relationships among variables for frequent and regular occurring events.
3.
Develop a model using an analogy, example, or abstract representation to describe a scientific principle or design solution.
4.
Develop and/or use models to describe and/or predict phenomena.
5.
Develop a diagram or simple physical prototype to convey a proposed object, tool, or process.
6.
Use a model to test cause and effect relationships or interactions concerning the functioning of a natural or designed system.
Student challenges
1.
The predictive, interpretive, and analytic aspects of models often are ignored (Ost, 1987).
2.
Students tend to view models primarily as physical copies of phenomena rather than as tools in the service of theory construction and testing (Grosslight et al., 1991).
3.
Students struggle to coordinate their understanding of scientific phenomena and representations of those phenomena (Rappoport & Ashkenazi, 2008).
4.
Students have difficulty explaining how models including diagrams and illustrations can be used to explain observed macroscopic phenomena (Stieff, 2011).
Constructing Explanation and Designing Solutions
1.
Construct a scientific explanation based on valid and reliable evidence obtained from multiple sources (including the students’ own experiments) consistent with scientific knowledge, principles, and theories.
2.
Apply scientific reasoning to show why the data or evidence is adequate for the explanations or conclusions.
Scientific Explanation:
This is a written or oral response to a question that requires students to analyze data and interpret that data with regard to scientific knowledge. Our explanation framework includes three components: claim, evidence, and reasoning.
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● Claim: a testable statement or conclusion that answers the original question.
● Evidence : scientific data that supports the student’s claim. This data can come from an investigation that students complete or from another source, such as observations, reading material, archived data, or other sources of information. The data needs to be both appropriate and sufficient to support the claim.
● Reasoning : a justification that shows why the data counts as evidence to support the claim and includes appropriate scientific principles. The reasoning ties in the scientific background knowledge or scientific theory that justifies making the claim and choosing the appropriate evidence.
Prior-Knowledge
In Grades 3-5, students use evidence in constructing explanations that specify variables that describe and predict phenomena.
1.
Construct an explanation of observed relationships.
2.
Use evidence to construct or support an explanation or design a solution to a problem.
3.
Identify the evidence that supports particular points in an explanation
Student challenges
1.
Students often had difficulty supporting their scientific claims (Sadler, 2004).
2.
Students provided with more data than appropriate for the evidence for a particular claim had difficulty in differentiating between appropriate and inappropriate evidence (McNeill & Krajcik,
2008).
3.
Students had difficulty providing reasoning for why they chose the evidence (Bell & Linn, 2000).
3. Unpacking Crosscutting Concepts
Energy and Matter
● Tracking how energy and matter flows into, out of, and within systems helps in understanding a system’s behavior.
1.
Matter is conserved because atoms are conserved in physical and chemical processes.
2.
Within a natural or designed system, the transfer of energy drives the motion and/or cycling of matter.
3.
Energy may take different forms (e.g. energy in fields, thermal energy, energy of motion).
4.
The transfer of energy can be tracked as energy flows through a designed or natural system.
Prior-Knowledge
In Grades 3-5, students learn matter is made of particles and energy can be transferred in various ways and between objects. Students observe the conservation of matter by tracking matter flows and cycles before and after processes and recognizing the total weight of substances does not change.
1.
Matter is made of particles.
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2.
Energy can be transferred in various ways and between objects.
3.
Matter flows and cycles can be tracked in terms of the weight of the substances before and after a process occurs.
4.
The total weight of the substances does not change. This is what is meant by conservation of matter. Matter is transported into, out of, and within systems.
Student challenges
1.
The relationship between matter, forces and energy is difficult for students to explain and apply
(Boo, 1998; Teichert & Stacy, 2002; Taber, 2009).
LP C-7: Students should be able to construct an explanation to show that in a chemical reaction, the total amount of matter does not change, therefore mass is conserved.
LP C-8: Students should be able to construct a model to show that the total number of atoms do not change after reaction, therefore mass is conserved.
LP C-9: Students should be able to provide an argument that a chemical reaction has occurred using arrangement of atoms in molecule.
LP C-7: Students should be able to construct an explanation to show that in a chemical reaction, the total amount of matter does not change, therefore mass is conserved.
DCI Practice CCC
PS1.B. Chemical reaction
● In a chemical process, the
● atoms that make up the original substances are regrouped into different molecules
The total number of each type of atom is conserved, and thus the mass does not change.
Construct an Explanation:
Claim, Evidence, and
Reasoning.
Energy and Matter:
Matter is conserved because atoms are conserved in physical and chemical processes.
Evidence
Students’ explanations should include:
Claim: The total amount of matter does not change in a chemical reaction.
Evidence: The products have the same mass as the reactants.
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Reasoning: In a chemical reaction, the products have the same mass as the reactants or mass is conserved so the total amount of matter does not change. Atoms of an element have the same mass. The mass of one element are different from other elements.
Additional Knowledge, Skills, and Ability
1. Students know that molecules are built from groups of atoms.
2. Molecules of a substance have their own characteristic properties and formula that are different from other substances. All molecules of a substance are the same.
3. Atoms of an element have the same mass and properties. The mass and properties of one element are different from other elements.
Characteristic Task Features
1.
Task presents simple chemical reaction in which simple molecules react.
2.
Task includes evidence of noticeable new physical or chemical properties.
3.
Task includes evidence that mass is conserved.
4.
Task will not include the use of atomic masses, balancing symbolic equations, or intermolecular forces.
Variable Task Features
1. Give a variety of simple chemical reactions to show the mass is conserved in all chemical reactions.
2. For simple chemical reactions, changes should be easy to observe, such as producing gas, forming precipitation, and changing color.
LP C-7-1 A model shows what happens before and after the combustion of methane. Write a scientific explanation about the expected total mass before and after the chemical reaction occurs.
LP C-7-2 Based on what is shown in this model, write a scientific explanation supporting a claim that a chemical reaction has occurred or not occurred.
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