Download Chemical Reactions

Toward High School Biology: Helping Middle School
Students Make Sense of Chemical Reactions
Jo Ellen Roseman
Director Project 2061
Principal Investigator
Biennial Conference on Chemical Education
Penn State University
July 29, 2012
Flow of the Paper Set
l Defining the targeted knowledge
l Curriculum development
l Professional development and
teacher materials
l Student measures and findings
l Teacher measures and findings
2
Coherence is the Goal
“Black and White and Ten Red”
Alexander Calder, 1957
“The only possible way in which individual
knowledge can keep proportional pace with
the surge of available knowledge is through
a grasp of the relatedness of knowledge.’’
Jerome Bruner, 1960
Sample Item from Project 2061’s Assessment
A table is made from wood that is cut from a tree. Where did most
of the material that makes up the table originally come from?
A. From sunlight
B. From oxygen in the air
C. From minerals in the soil
D. From carbon dioxide in the air
% Students Selecting Answer Choice C or D
Where did most of the material that makes up a wooden table originally
come from?
100%
Minerals in the soil
90%
80%
70%
60%
50%
40%
CO2 in the air
30%
20%
10%
0%
7
8
9
10
11
Grade
12
Entering Juniors Grad.
College
Students
Across items assessing ideas about
matter and energy, students commonly:
l  are confused about what is conserved in chemical reactions
(atoms, molecules, energy),
l  do not associate growth with
an increase in mass (and hence
have no need to account for it),
l  think that the mass of gases is inconsequential (and hence
doesn’t contribute significantly to growth), and
l  do not associate the growth and functioning of organisms with
chemical reactions.
8
The Intervention: A New Curriculum Unit
l  5-6 week replacement unit for 8th grade students
l  Focuses on a coherent set of ideas about chemical reactions and
conservation in non-living and living systems that are central to science
standards (Including A Framework for K-12 Science Education)
l  Engages students in interesting and appropriate phenomena that provide
evidence for the ideas and for their explanatory power
l  Uses a variety of modeling tasks
to guide students in interpreting the
phenomena in light of the rearrangement and conservation of atoms during
chemical reactions
Measures of Quality, Feasibility, & Promise
l  Curriculum quality: satisfying criteria (coherent content + instructional
support), conveying science content and design rationale to teachers
l  Feasibility of use: ability of a range of teachers to use it as designed
9
l  Promise: improved student understanding of the set of ideas
The development of both the curriculum and
the assessment starts with the identification
and clarification of learning goals.
l  Identify the learning goals to serve as the focus of development
of both the curriculum unit and assessment items.
l  Clarify the expectations of the learning goals, including their
boundaries.
l  Identify common misconceptions that might interfere with student
learning. (These will be used as distractors in multiple choice
items and explicitly addressed in the curriculum).
10
Chemistry Learning Goals
l  Many substances react chemically with other substances to form new
substances with different characteristic properties. When substances
react, the atoms that make up the molecules of the reactants
rearrange to form the molecules of the products. The products have
different properties because they are made up of different molecules.
l  Mass is conserved during chemical
reactions because the total
number of each kind of atom making up the molecules of the
reactants is the same as the total number of each kind of atom
making up the molecules of the products. (If the measured mass
changes it is because atoms have entered or left the system).
l  Carbon-containing monomers can react to form carbon-containing
polymers (and water molecules) that form visible structures. As in all
chemical reactions, atoms are rearranged, not created or destroyed.
11
Excerpt from a Clarification
…When substances react to form new substances, the atoms that make
up the molecules of the reactants rearrange to form the molecules of
the products...
Students are expected to know that:
l  During a chemical reaction, the atoms that make up the molecules of the
reactants rearrange to form the molecules
of the products.
l  It does not matter how many atoms are rearranged, as long as some
atoms of the product molecules are linked to atoms they were not linked
to in the reactant molecules.
l  The products of a chemical reaction are made of the same types of atoms
as the reactants, i.e., the atoms themselves do not change during the
reaction.
12
Excerpt from a Clarification
Boundaries:
l  Students are not expected to know the term “bond” or how chemical
bonds are formed or broken during chemical reactions.
l  Students are not expected to know the parts of atoms or that electrons
are involved in bonding.
13
Commonly Held Student Ideas
l  Atoms can be created during a chemical reaction. (AAAS Project
2061, n.d.)
l  Atoms can be destroyed during a chemical reaction. (AAAS
Project 2061, n.d.)
l  The atoms of the reactants of a chemical reaction are
transformed into other atoms (Andersson,
1986).
14
Biochemistry Learning Goals
l  Animals use polymers from food to make a variety of other
polymers that make up their body structures.
l  Plants use glucose monomers they make to make a variety of
polymers that become part of their body structures.
l  During the chemical reactions animals and plants use to build
body structures, atoms are rearranged,
not created or destroyed.
The increase in the number of atoms making up the bodies of
animals and plants results from a decrease in the number of
atoms in their surroundings.
15
Excerpt from a Clarification
Animals use polymers from food to make a variety of other polymers that
make up their body structures.
Students are expected to know that:
l  Except for bone, animal body structures (e.g., muscles, tendons, skin,
scar tissue) are made mostly of proteins.
l  Proteins are polymers made of amino
acid monomers linked together.
The amino acid monomers are composed primarily of carbon, hydrogen,
oxygen, and nitrogen atoms.
l  Animals need about 20 different kinds of amino acids to build all the
proteins needed to make their body structures.
l  Animals break down polymers from food to obtain the monomers they
need to build polymers that make up their body structures.
16
l  The processes by which molecules from food become part of an animal’s
body structures involve chemical reactions.
Excerpt from a Clarification
Boundaries:
l  Students are not expected to know that humans can make some, but not
all, of the 20 amino acids and, therefore, must obtain these “essential”
amino acids from food.
l  Students are not expected to know the chemical or structural formulas of
particular proteins. (However, students should be able to compare
products to determine if any atoms
structural formulas of reactants and
are rearranged.)
17
Commonly Held Student Ideas
l  Matter is created or destroyed, rather than transformed, in biological
processes. (Smith & Anderson, 1986)
l  None of the atoms from food becomes part of the body structures of
animals. All of the food an animal eats goes through the digestive
system and ends up as waste. (AAAS Project 2061, n.d.)
l  Most of a plant's mass comes from minerals that the plant takes in
from the soil (Vaz et al, 1997).
18
Once the learning goals have been clarified,
the assessment development and curriculum
development proceed in parallel:
l  Assessment items are developed, using commonly held student ideas
as distractors, and are pilot tested
and revised before being used in pretests and post-tests of student learning.
l  A coherent content storyline is developed for the curriculum unit,
organizing key ideas from the learning goals into a logical sequence that
takes account of commonly held student ideas.
19
ITEM: The diagram below shows models of the molecules that make up two
different substances. In the diagram, atoms are represented by circles, and the
molecules are represented by two or more circles connected to each other. The
different colored circles represent different types of atoms.
Which of the following could represent one of the molecules that result from the
chemical reaction between these two substances? Why?
A.
20
Because nothing happens
to the structure of the molecules
during a chemical reaction.
B.
Because some of the atoms are now connected to different
atoms than they were in the starting molecules.
C.
Because the molecules that result from a chemical reaction
have to include every type of atom from the starting molecules.
D.
Because new types of atoms are formed during chemical
reactions.
SB04-2
ITEM: A rabbit eats some grass. What happens to the grass once it is
inside the rabbit’s body?
Rabbit eating grass. Photo (CC) by Larry D. Moore.
A. All of the grass is digested down to individual atoms that are destroyed,
and disappears.
B. All of the grass goes through the digestive system and ends up as
waste.
C. Some of the grass goes through chemical reactions and becomes part of
the rabbit’s body.
D. Some of the grass gets added to the rabbit’s body without going through
any chemical reactions.
SB18-1
Content Story Line for the Curriculum Unit
A Content Story Line is a logical sequence of ideas that, when linked
to evidence, contributes to student understanding of the learning
goals.
To remind us of the importance of providing evidence for each idea
and helping students link the evidence
to the idea, we organize unit
development in a table that lists the idea (claim), evidence, and
reasoning for each lesson.
Evidence consists of observable phenomena and/or data.
Reasoning consists of the logical step-by-step argument needed to
link the evidence to the claim, often involving models.
22
Content Story Line for the Curriculum Unit
A Content Story Line is a logical sequence of ideas that, when
supported by evidence, contributes to student understanding of the
learning goals.
To remind us of the importance of providing evidence for each
science idea and helping students
link the evidence to the idea, we
organize unit development in a table that lists the idea (claim),
evidence, and reasoning for each lesson.
Evidence consists of observable phenomena and/or data.
Reasoning consists of the logical sequence of steps of the argument
linking the evidence to the claim, often involving models.
23
Excerpt from the Chemistry Content Story Line
Sequence of Ideas for Chapter 1
When substances interact, they can form substances with different properties from the
starting substances.
If two substances have different properties then they are different substances.
Different substances have different properties because they are made up of different
molecules.
Although new substances form, they are made up of the same kinds of atoms as the
starting substances.
During chemical reactions, the atoms of the molecules of the reactants break apart from
each other and rearrange to form the molecules of the products. No atoms are created or
destroyed, so the number of each kind of atom in both reactants and products is the same.
Polymers are made during chemical reactions that link monomers together. The monomers
and polymers have different properties and, hence, are different substances.
Polymers can link together to form visible structures.
As in all chemical reactions, atoms rearrange during polymer formation, but the number of
each kind of atom in both reactants and products is the same.
24
Excerpt from the Chemistry Content Story Line
Sequence of Ideas for Chapter 2
In chemical reactions, the mass of the products is always the same as the mass of the
reactants, because atoms are not created or destroyed.
If the measured mass of the products is less than the measured mass of the reactants, then
some matter/atoms must have left the system. This can occur if a gas is produced and is
able to leave the system.
If the measured mass of the products is greater than the measured mass of the reactants,
system. This can occur if a gas is a
than some matter/atoms must have entered the
reactant and is able to enter the system.
25
Excerpt from the Biochemistry Content Story Line
Sequence of Ideas for Chapter 3
As living things grow, they increase in size and mass because their bodies are making new
materials. Even when an entire organism doesn’t appear to be getting any bigger, new
materials are still being made.
Animal-based foods, and the animals themselves, are made up mostly of proteins.
Animals use proteins from food to make the proteins that make up their body structures.
Proteins are polymers made up of amino acid monomers. Nearly all proteins can be made
from 20 different amino acid monomers, which
are made up mostly of carbon, hydrogen,
oxygen, and nitrogen atoms. Different proteins are composed of different amounts of the
amino acids.
During chemical reactions in the digestive tract, proteins are broken down to amino acids.
During the break down of proteins to amino acids, atoms are not created or destroyed, just
rearranged.
Animals use the amino acids to build proteins that make up their body structures. When an
animal grows, the number of protein polymers making up its body increases.
During the chemical reactions involved in animal growth, atoms are not created or
destroyed, just rearranged. As the number of atoms making up an animal’s body increases,
the number of atoms in its surroundings decreases.
26
Excerpt from the Biochemistry Content Story Line
Sequence of Ideas for Chapter 4
Plant-based foods, and the plants themselves, are made up mostly of carbohydrates. Plant
seeds have higher amounts of proteins and fats compared to plant body structures such as
leaves, stems, and roots.
The carbohydrates that make up most plant body structures are polymers made from
glucose monomers, which are composed of C, H, and O atoms.
During chemical reactions, plants use glucose monomers to make carbohydrate polymers
and water molecules. When plants make carbohydrate polymers from glucose monomers
atoms are not created or destroyed, just rearranged.
Plants make glucose monomers from carbon dioxide molecules in the air and water
molecules. (Because the C and O atoms making up carbohydrate polymers come from
CO2, most of a plant’s mass comes from CO2 in the air). During the chemical reactions
involved in plant growth, atoms are not created or destroyed, just rearranged. As the
number of atoms making up a plant’s body increases, the number of atoms in its
surroundings decreases.
Plants make amino acid monomers from glucose and a source of nitrogen atoms (from the
soil). Like animals, plants use the amino acid monomers to make protein polymers and
water molecules. When plants make amino acids, atoms are not created or destroyed, just
27rearranged.
Core Ideas (From NRC Science Framework)
PS1.B: Chemical Reactions
Many substances react chemically with other substances to form
new substances with different properties. This change in
properties results from the ways in which atoms from the original
substances are combined and rearranged in the new substances.
However, the total number of each type of atom is conserved in
any chemical process, and thus mass does not change either...
(grade 8)
Understanding chemical reactions and the properties of elements is
essential not only to the physical sciences but also is foundational
knowledge for the life sciences and the earth and space sciences.
28
LS1.C: Organization for Matter and Energy Flow in Organisms
Plants, algae, and many microorganisms use the energy from
light to make sugars (food) from carbon dioxide from the
atmosphere and water through the process of photosynthesis,
which also releases oxygen. These sugars can be used
immediately or stored for growth or later use. Animals obtain food
from eating plants or eating other animals. Within individual
organisms, food moves through
a series of chemical reactions in
which it is broken down and rearranged to form new molecules, to
support growth, or to release energy… (Grade 8)
The sugar molecules thus formed [in photosynthesis] contain
carbon, hydrogen, and oxygen; their hydrocarbon backbones are
used to make amino acids and other carbon-based molecules that
can be assembled into larger molecules (such as proteins or
DNA), used to form new cells. (Grade 12)
29
Scientific Practices (From NRC Science Framework)
Developing and Using Models
Represent and explain phenomena with multiple types of models and
move flexibly between model types when different ones are most useful
for different purposes.
Constructing Explanations
Construct explanations of phenomena
using knowledge of accepted
scientific theory and linking it to models and evidence.
Engaging in Argument from Evidence
Recognize that the major features of scientific arguments are claims,
data, and reasons and distinguish these elements in examples.
30
Crosscutting Concepts (From NRC Science
Framework)
Systems and system models
Defining the system under study—specifically its boundaries and
making explicit a model of that system—provides tools for
understanding and testing ideas that are applicable throughout
science and engineering.
Energy and Matter: flows, cycles, and conservation
Tracking fluxes of energy and matter into, out of, and within
systems helps one understand the systems’ possibilities and
limitations.
31