The Grand Gel Challenge
Physical and Chemical Changes of Properties
Hanin Bearat
November 15-16, 2010
LESSON OVERVIEW
This lesson is designed to cover the basics of physical changes and chemical reactions, which is
necessary for 8th grade science. It is assumed that the students will not have had exposure to
the concepts prior to the lesson. Definitions of physical change and chemical change will be
derived through experimentation with some chemical solutions. Examples of these changes of
properties will also be discussed in class. Along with the definitions/examples powerpoint
presentation, a worksheet will be given to the students to fill out and take notes. The lesson
also will explore gels and their applications in the biomedical field. Students will design a gel for
a particular medical application and present their findings on a poster to the class. To conclude,
a video will be shown on the research and various uses of gels.
KEY WORDS: physical change, chemical change, reaction, pH, temperature, gel/hydrogel,
biomedical applications.
GRADE LEVEL: This lesson is designed for 8th grade science students.
DURATION: 2 (70min) class periods.
OBJECTIVES
The lesson is designed for students to learn the following:
 Characteristics of physical and chemical changes and how to differentiate between
them
o How two substances can be combined to form a new one through a chemical
reaction
o How different stimuli can cause a physical change to take place, and that it can
be reversed
 How motion of particles differ in a gas, liquid or solid state
 Experiment with polymer gels, with both physical and chemical polymer solutions
 Design-a-gel
 Present observations and designed gels to the class
VOCABULARY
pH: Amount of hydrogen ions which determines whether solution is acidic or basic.
Density: The ratio of mass of a substance to its volume.
Precipitate: A solid that forms from a solution during a chemical reaction.
Boiling Point: The temperature at which a substances changes from liquid to gas.
Melting Point: The temperature at which a substance changes from solid to liquid.
Phase: The state matter is in (solid, liquid, or gas).
Polymer: A large molecule in which many smaller molecules are bonded together
Evaporation: Process when vaporization takes place only on surface of liquid.
Reactivity: The ease and speed by which an element combines/reacts with other elements and
compounds.
Reactants: Initial substances that are mixed together to form a chemical reaction
Products: Final or new substance created from a chemical reaction
Condensation: Change from gaseous to liquid state of matter.
Solubility: Measure of how much solute can dissolve in a given solvent at a given temperature.
STANDARDS
The Arizona and National standards for this lesson are the following:
 STRAND 1: Inquiry Process
o PO1: demonstrate safe behavior and appropriate procedures
o PO3: conduct a controlled investigation to support or reject a hypothesis
o PO4: perform measurements using appropriate scientific tools
o PO5: keep a record of observations, notes, sketches, questions, and ideas using
written and/or computer logs
 STRAND 3: Science in Personal & Social Perspective, Concept 2 (Science & Technology in
Society)
o PO1: propose viable methods of responding to an identified need or problem
o PO2: compare solutions to best address an identified need or problem
o PO3: design and construct a solution to an identified need or problem using
simple classroom materials
 STRAND 5: Physical Sciences, Concept 1
o PO1: identify different kinds of matter based on physical properties
o PO2: identify different kinds of matter based on chemical properties
o PO3: identify types of evidence that a chemical reaction has occurred
SAFETY
All students are required to wear goggles and gloves at all times.
PROCEDURE
Day 1, Part A: Gel Experimentation
 In groups of 4, students will investigate physical change with thermosensitive polymer
solutions (10min)
 They will also investigate chemical change by mixing two polymer solutions, which will
undergo a chemical reaction to form a gel (15min)
 Students will take notes on the experiment conditions, record observations and data,
and formulate questions
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We will discuss the physical and chemical changes observed in the gel experiment and
relate to definitions (5-10min)
We will then go through the definitions and examples of physical and chemical changes
with a powerpoint presentation, accompanied by a worksheet (5-10min)
Video about physical and chemical changes, and examples
Day 1, Part B: Design-a-gel
 We will discuss the use of gels and what similar gels can be used for (related to medical
applications) (5-10min)
 We will also talk about what changes/alterations can be made to the gels to optimize
them or to result in different properties or to be used in other medical applications
(5min)
 Students will identify (in groups of 4) a medical condition/application for which gels can
be used as a treatment method, and design a gel for that purpose (brainstorm
diseases/conditions, ideas on the gel properties needed, addition of components to the
gel, what want gel to do and how to accomplish task) (10-15min)
Day 2: Design-a-gel Poster & Presentation
 Students review their ideas on their gel (medical condition and gel properties) and
report the gel on a poster (15-20min)
 Students then present ideas to the class (35-40min)
 After all presentations finished, wrap up with a discussion of the different gels and a
powerpoint presentation on current research being done on gels and medical
applications (10-15min)
 Relate the current research being done with the gels designed by the students (5min)
 Video of various medical applications of gels (8min)
STUDENT MISCONCEPTIONS
The National Science Digital Library Science Literacy Maps lists some of the common student
misconceptions observed in the physical sciences. I have highlighted two main misconceptions
faced in the subjects related to the lesson and how they will be addressed in class.
Student Misconception #1 – States of Matter:
Students have difficulty understanding the motion of particles in solids, liquids and gases. To
address this issue, students will be asked to note the changes in the properties of the polymer
solutions (solid vs. liquid) during the experiment. How does the liquid solution behave or look
differently than its solid counterpart? What do you think attributes to that difference? If you
were put in a tub filled with water vs. if you were in a tub filled with jello, how would your
movements be different? And why? We will then discuss how this can relate to particles in the
different states and their respective motion (solid, liquid, gas). A particle in a liquid (tub of
water), can easily move around, whereas a particle in a solid (tub of jello) is constricted in
movement.
Student Misconception #2 – Chemical Reactions:
Students do not see chemical changes as interactions and do not understand substances can be
formed by recombination of atoms in the original structures. To address this misunderstanding,
students will see firsthand how chemical changes occur when they will be mixing the two
polymer solutions together to form a gel. They will be asked to comment on what they think is
happening. What did you start off with? What happened when you mixed the two components
together? What did you end up with, after mixing? Are the solutions that you started off with
the same as the final solution? What do you think allowed for this change to take place (liquid
to gel)? We will talk about how two different solutions (both liquids), when mixed together,
undergo a chemical reaction to form a new substance, completely different from the initial
solutions (a gel). We will also discuss how this happens due to recombination of the atoms in
the original structures to form a new structure.
ASSESSMENT
Various methods for assessment will be utilized and they include:
 Formative assessment (self-reflective, how student is involved in asking/answering
questions, working with other students, participating in activities, etc.)
 Students creating notes involving questions, observations, sketches/notes, design-a-gel
 Collaborate and use “jig-saw” approach to create posters about their gels
 Presentation of results (on posters) to the class
 Participation, effort, use of intelligence, behavior and safety graded out of 5 points for
the overall lab activity
NOTE
Depending on the knowledge and the exposure to the subject that the students have, this
lesson can be tailored to those needs. This was prepared for students in “gifted” science
programs who were not exposed to the subject of physical/chemical changes but had been
slightly exposed to some aspects of use of gels.
ALTERNATIVES
In the event that the chemical compounds cannot be purchased or made, other simpler
materials can be used to perform this activity. For example, to demonstrate the physical
changes similarly to the temperature-sensitive gel, Jell-O can be used. When the Jell-O powder
is added in water and heated, it is found as a solution where the chains of the gelatin present in
Jell-O are floating around. However, as it cools, the chains form junctions and reconnect to try
to reform into its original helical structure and in the meantime, trap water in its cavities. This
forms a gel. It is a reversible process because if re-heated, the gel goes back into a solution.
Although Jell-O is not used in medicine for treatment of diseases, one can point out that similar
materials, which form gels, are being used for medical purposes.
An alternative to using the chemicals proposed here to explore chemical changes (through a
chemical reaction), one can use calcium chloride dissolved in water and sodium alginate also
dissolved in water. When the calcium chloride (salt) solution is combined with sodium alginate
(originates from algae), a gel forms upon contact. The formation of a gel results when the
calcium replaces the sodium, upon contact of the two solutions. This is a chemical reaction,
since there is a change in the composition of the substances and a new substance is formed
(from the mixing of two liquid solutions, a solid gel is formed). This is also not reversible. Prior
to using these materials, make sure to read more about them, how to procure them and how to
use them.