LESSON 11: Diaper Polymers

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LESSON 11: Diaper PolymersESTIMATED TIME Setup: 10 minutes | Procedure: 5–10 minutes

• DESCRIPTIONUse crystals found in diapers to absorb water andillustrate the properties of super-absorbent polymers.

• OBJECTIVEThis lesson introduces students to molecules,monomers, and polymers. Students will observe thediffusion of water in and out of super-absorbentpolymer crystals found in diapers. The lesson can besimplified to focus on just the process of diffusion.

• CONTENT TOPICSScientific inquiry; states of matter; properties ofmatter; diffusion; polymers

• MATERIALSo Disposable diapers

o Distilled water o Graduated cylinder (or measuring cups) o Table salt o Paper bag o Spoons o Paper cups o Magnifying glass (optional)

Always remember to use the appropriate safetyequipment when conducting your experiment.

Refer to the Safety First section in the Resource Guideon pages 421–423 for more detailed information aboutsafety in the classroom.

Jump ahead to page 143 to view theExperimental Procedure.

OBSERVATION & RESEARCH

BACKGROUNDA molecule is the smallest particle of an element or

compound that retains the chemical properties of that

element or compound. It is composed of two or more

atoms chemically bonded together by an exchange or

sharing of electrons. At the beginning of the 20th century,

chemists learned how to create special molecules by

combining many smaller molecules in a regular pattern.

These large molecules are called polymers. Polymers are

long, chain-like molecules that are formed by connecting

many repeating units (monomer units). The most

common polymers are made of long chains of carbon

atoms. A monomer is a single molecule capable of

combining with other similar molecules.

The super-absorbent polymer found in many brands of

disposable diapers is called sodium polyacrylate. This

long polymer is able to absorb large amounts of water

because the sodium ions attached to it attract water.

These ions attract water into the polymer by diffusion or

osmosis. Diffusion is the movement of particles from an

area of high concentration to an area of low

concentration. Osmosis is the diffusion of water across a

semi-permeable membrane.

NATIONAL SCIENCE EDUCATION STANDARDS SUBJECT MATTERThis lesson applies both Dimension 1: Scientific and Engineering Practices and Dimension 2: Crosscutting Conceptsfrom “A Framework for K–12 Science Education,” established as a guide for the updated National Science EducationStandards. In addition, this lesson covers the following Disciplinary Core Ideas from that framework: • PS1.A: Structure and Properties of Matter • PS1.B: Chemical Reactions • ETS2.B: Influence of Engineering, Technology, and Science on Society and the Natural World (see Analysis & Conclusion)

You Be The Chemist® Activity Guide | page 141

LESSON 11: Diaper PolymersWhen sodium polyacrylate is exposed to water, the

higher concentration of water outside the polymer (and

higher concentration of sodium ions inside the polymer)

draws the water into the molecule through osmosis.

Sodium polyacrylate will continue to absorb water until

there is an equal concentration of water inside and

outside the polymer. Each sodium polyacrylate molecule

is able to attract and hold thousands of water molecules.

Table salt is primarily composed of the compound

sodium chloride. When sodium chloride is added to the

hydrated polymer, the sodium ions from the salt attract

the water. As a result, water molecules diffuse back out

of the polymer.

FORMULAS & EQUATIONSSodium polyacrylate is known as a super-absorbent

polymer because it has the ability to absorb several

hundred times its mass in water.

It is a polymer that consists of repeating units of the

monomer CH2CH(CO2Na)- or (C3H3NaO2)n. The n stands for any number of molecules.

Common table salt is mainly made up of the compound

sodium chloride.

The chemical formula for sodium chloride is NaCl.

Most table salts are made of about 97–99% NaCl. The

remaining 1–3% is usually iodine and other ingredients.

CONNECT TO THE YOU BE THECHEMIST CHALLENGE

For additional background information, please

review CEF’s Challenge study materials online at

http://www.chemed.org/ybtc/challenge/study.aspx.

• Additional information on molecules can befound in the Atomic Structure section of CEF’sPassport to Science Exploration: The Core ofChemistry.

• Additional information on polymers can be foundin the Industrial Applications of Chemistrysection of CEF’s Passport to Science Exploration:Chemistry Concepts in Action.

• Additional information on diffusion can be foundin the Classification of Matter section of CEF’sPassport to Science Exploration: The Core ofChemistry.

HYPOTHESIS

uAdding water to the super-absorbent

polymer found in diapers will cause the

polymer to swell as water diffuses inside. When table

salt is added to the swollen polymer, the water will

diffuse back out of the polymer.

Fun FactEver wonder what happens

when astronauts are on a long

space journey without a port-a-

potty handy? They need

super-absorbent

polymers too!

http://www.chemed.org/ybtc/challenge/study.aspx


LESSON 11: Diaper Polymers

LOWER GRADE LEVELS/BEGINNERSDESCRIPTIONUse polymer crystals found in diapers to illustrate theprocess of osmosis (diffusion).

OBJECTIVEThis lesson explores properties of matter and illustrates theprocesses of diffusion and osmosis.

OBSERVATION & RESEARCHDifferent states of matter exhibit different properties.Liquids and gases are considered fluids. A fluid is anysubstance made up of particles that flow or move freely. A fluid easily changes shape when a force is applied. For example, if you push on a balloon filled with gas, you can easily change its shape. Likewise, if you push on a water balloon, you can change the shape of the balloonfilled with water as well.

Fluids can undergo a process called diffusion. Diffusionis the movement of particles from an area of highconcentration to an area of low concentration. The particles will move at random from an area with many particles to an area with few particles. Diffusionwill continue until the particles are spread evenlythroughout an area. Water undergoes a special type of diffusion called osmosis. Osmosis is the diffusion of water across a semi-permeable membrane. Osmosis is an important process in our bodies because it allows waterto pass into and out of our cells.

The super-absorbent substance, called sodium polyacrylate,is found in many brands of disposable diapers. It usesosmosis to soak up water. Because there is a higherconcentration of water outside the sodium polyacrylate, it draws in the water through osmosis. Each sodiumpolyacrylate molecule is able to attract and hold thousandsof water molecules.

Likewise, table salt is primarily composed of sodiumchloride. When sodium chloride is added to the hydratedsodium polyacrylate, the water molecules diffuse back outof the polymer.

HIGHER GRADE LEVELS/ADVANCED STUDENTSPerform the experiment as described on page 143, butchallenge your students to determine what type of changeis occurring and to support their decision. There is noeasy answer to this one!

The polymer sodium polyacrylate is called super-absorbentbecause it is able to absorb much more water than its ownweight. Polymers are formed through a specific bondingprocess called cross-linking. Cross-linking is the formationof chemical bonds between complex molecules ormolecular chains, such as polymers. Cross-linking causesthe polymer chains to stick together and overlap, forming anet-like or web-like structure, instead of being spreadstraight out in a long chain.

Although sodium polyacrylate looks like salt crystals, thepolymer is very complex. It has so many cross-linked bondsbetween its molecules that adding water causes the polymerto swell and allows more water to diffuse into the spacesinside.

Think of a balloon. A balloon is made of a polymersubstance that will expand to allow air and water inside.Its shape changes when this occurs but its chemicalcomposition does not. Likewise, when a sodiumpolyacrylate crystal is exposed to water, it expands andallows the water to diffuse inside the polymer.

CONNECT TO THE YOU BE THECHEMIST CHALLENGE

For additional background information, pleasereview CEF’s Challenge study materials online athttp://www.chemed.org/ybtc/challenge/study.aspx.

• Additional information on fluids, diffusion, andosmosis can be found in the Classification ofMatter section of CEF’s Passport to ScienceExploration: The Core of Chemistry.

DIFFERENTIATION IN THE CLASSROOM

http://www.chemed.org/ybtc/challenge/study.aspx


LESSON 11: Diaper PolymersEXPERIMENTATION

As the students perform the experiment, challenge them to identify the independent, dependent, and controlled variables,

as well as whether there is a control setup for the experiment. (Hint: If you use different diapers, will you get the same

results?) Review the information in the Scientific Inquiry section on pages 14–16 to discuss variables.

EXPERIMENTAL PROCEDURE

Part One: Obtaining the Polymer Crystals

1. Remove the cotton-like fiber filling from a

disposable diaper. (If you look at the filling through

a magnifying glass, you will notice tiny flakes or

crystals attached to the filaments. In some brands,

these filaments are obvious without a magnifying

glass.)

2. Carefully, shred the fiber filling into smaller pieces.

Make sure to include any leftover crystals that may

remain on the diaper!

3. Place the filling in a paper bag and shake it

vigorously for a minute. The crystals will dislodge

and collect in the bottom of the bag.

4. Lift the cotton fibers carefully from the bag and

dispose of them, leaving the crystals in the bottom

of the bag.

The fine powder released when shaking the

crystals from the diapers can irritate the

respiratory system if inhaled. You may want to obtain

the crystals for the students before the lesson.

Otherwise, have your students wear small filter masks

that cover their mouths and noses, as well as safety

goggles to protect their eyes. If you obtain the crystals

for them, be sure to wear a filter mask and safety

goggles yourself.

Part Two: Experiment

1. Place a spoonful of the crystals in the bottom

of a paper cup.

2. Slowly pour 200 mL (or approximately 4/5 cup)

of distilled water into the cup. Stir gently and

allow the cup to stand for about five minutes.

3. Observe the substance in the cup.

4. Sprinkle table salt on the substance in the cup and

stir. Keep adding salt until it liquefies.

Distilled water is a better choice for

this experiment because it does not

contain any ions that would compete with the

sodium in the polymer. Tap water also works but

not as effectively.

DATA COLLECTIONHave students record data in their science notebooks or on the following activity sheet. What changes do students

notice between the original polymer and the polymer once it has absorbed the water? Have students answer the

questions on the activity sheet (or similar ones of your own) to guide the process.

Fiber filling with crystals

Majority ofcrystals collectedat the bottom


LESSON 11: Diaper PolymersANALYSIS & CONCLUSION

Use the questions from the activity sheet or your own

questions to discuss the experimental data. Ask students

to determine whether they should accept or reject their

hypotheses. Review the information in the Scientific

Inquiry section on pages 14–16 to discuss valid and

invalid hypotheses.

ASSESSMENT/GOALS

Upon completion of this lesson, students should be able

to …

• Apply a scientific inquiry process and perform anexperiment.

• Define and identify the properties of polymers and monomers.

• Differentiate between the processes of diffusion and osmosis.

• Define and give examples of fluids (see Differentiationin the Classroom).

• Explain the importance of osmosis in the humanbody (see Differentiation in the Classroom).

• Describe the process of cross-linking (seeDifferentiation in the Classroom).

MODIFICATIONS/EXTENSIONS

Modifications and extensions provide alternative methods

for performing the lesson or similar lessons. They also

introduce ways to expand on the content topics presented

and think beyond those topics. Use the following

examples, or have a discussion to generate other ideas as

a class.

• Before you start the lesson, add some crystals to apaper or Styrofoam™ cup without the students

knowing. Allow the students to watch you pour water

into the cup. Stir the water around a bit and then

invert the cup. Nothing should fall out. Ask students

for an explanation to test their knowledge. (Make

sure you test this first to be sure you have the right

amount of crystals and water to make this work.)

REAL-WORLD APPLICATIONS

• Super-absorbent polymers have other uses too. Thesepolymers may be used in special soils to store water

near a plant’s roots. The plant is then able to access

this water when less water is available, such as when

it hasn’t rained in a while. It also helps prevent

erosion from water runoff.

• Polymers can be found all over the place. Theyinclude rubber, plastics, Styrofoam™, and clothing

fibers, such as nylon and rayon. What other examples

can you find?

COMMUNICATION

Discuss the results as a class and review the activity sheet.

Review the information in the Scientific Inquiry section on

pages 14–16 to discuss the importance of communication

to scientific progress.

You Be The Chemist Activity Guides | page 145You Be The Chemist® Activity Guide | page 145

LESSON 11 ACTIVITY SHEET: Diaper Polymers

OBSERVE & RESEARCH

1. Write down the materials you observe. ________________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

2. Predict how these materials may be used. ______________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an

image of the example.

Term Definition Example (write or add image)

Molecule

Monomer

Polymer

Diffusion

Osmosis

4. Consider how crystals contained within a disposable diaper will react when water is added and why.

uWrite your hypothesis. ______________________________________________________________

______________________________________________________________________________________

______________________________________________________________________________________



ANALYZE & CONCLUDE

1. Describe the fiber filling of the diaper. ________________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

2. Why do you think there are crystals in the diaper? ______________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

3. What happens when you add water to the crystals? ______________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

4. Describe the polymer after the water is added. __________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

PERFORM YOUR EXPERIMENT

Part One:

1. Wearing the proper safety equipment, remove the fiber filling from a disposable diaper. Observe the filling.

2. Carefully shred the fiber filling into smaller pieces, and place the filling in a paper bag.

3. Shake the bag vigorously for a minute. (Be sure you are still wearing your safety gear!) The crystals will dislodge


4. Remove the fibers from the bag and dispose of them. Make sure the crystals remain in the bottom of the bag.

Part Two:

1. Place a spoonful of the crystals in the bottom of a paper cup.

2. Slowly pour approximately 200 mL of distilled water into the cup and observe.

3. Sprinkle table salt on the mass and stir. Keep adding salt until the properties of the mass change.

You Be The Chemist Activity Guides | page 147You Be The Chemist® Activity Guide | page 147


5. What happens when you add salt to the water-soaked polymer? ____________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

6. Is your hypothesis valid? Why or why not? If not, what would be your next steps? ____________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

2. What are other ways that super-absorbent polymers may be used? ________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

3. Provide other examples of diffusion. ________________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

SHARE YOUR KNOWLEDGE

1. Define the following key term. Then, provide an example of it by writing the example or drawing/pasting an image

of the example.


Fluid


LESSON 11 ACTIVITY SHEET: Diaper PolymersANSWER KEY: Below are suggested answers. Other answers may also be acceptable.

OBSERVE & RESEARCH

1. Write down the materials you observe. ________________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

2. Predict how these materials may be used. ______________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an

image of the example.


MoleculeThe simplest structural unit of an element orcompound that is made up of atoms held togetherby chemical bonds and maintains the chemicalproperties of the element or compound.

Monomer A single molecule capable of combining with othersimilar molecules to forrm a polymer.

Polymer A large molecule formed by combining manysmaller molecules (monomers) in a regular pattern.

Diffusion The movement of particles from an area of highconcentration to an area of low concentration.

OsmosisThe diffusion of water across a semi-permeablemembrane (a membrane that allows some ions ormolecules to pass through but not others).

4. Consider how crystals contained within a disposable diaper will react when water is added and why.

uWrite your hypothesis. ______________________________________________________________

______________________________________________________________________________________

______________________________________________________________________________________

Diapers may be used to absorb a liquid. Water may be used to drink, clean, or bathe.

Table salt may be used to add flavor to food. Together the materials may be used to observe the processes of diffusion and osmosis.

Diapers (super-absorbent crystals), table salt, water, magnifying glass ...

By adding water to the super-absorbent crystals found in diapers, the crystals will swell

as they take in the water. Adding salt to the swelled, gel-like polymer will cause the water to diffuse back out of the

polymer.



ANALYZE & CONCLUDE

1. Describe the fiber filling of the diaper. ________________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

2. Why do you think there are crystals in the diaper? ______________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

3. What happens when you add water to the crystals? ______________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

4. Describe the polymer after the water is added. __________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

PERFORM YOUR EXPERIMENT

Part One:

1. Wearing the proper safety equipment, remove the fiber filling from a disposable diaper. Observe the filling.

2. Carefully shred the fiber filling into smaller pieces, and place the filling in a paper bag.

3. Shake the bag vigorously for a minute. (Be sure you are still wearing your safety gear!) The crystals will dislodge


4. Remove the fibers from the bag and dispose of them. Make sure the crystals remain in the bottom of the bag.

Part Two:

1. Place a spoonful of the crystals in the bottom of a paper cup.

2. Slowly pour approximately 200 mL of distilled water into the cup and observe.

3. Sprinkle table salt on the mass and stir. Keep adding salt until the properties of the mass change.

The fiber filling of the diaper is soft, but strong. The fibers are woven together, which

makes them strong. Once the woven fiber is removed from the diaper lining, it can be torn into smaller pieces.

The crystals in the diaper are super-absorbent polymer crystals used to draw

in liquid and keep a baby’s bottom dry.

When you add water to the crystals, the water moves into the polymer

through osmosis (diffusion). The crystals swell from the added water.

The polymer is clear, thick, and soft like a gel. It is mushy, but it is not a fluid.



5. What happens when you add salt to the water-soaked polymer? ____________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

6. Is your hypothesis valid? Why or why not? If not, what would be your next steps? ____________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

2. What are other ways that super-absorbent polymers may be used? ________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

3. Provide other examples of diffusion. ________________________________________________________________

______________________________________________________________________________________________________

______________________________________________________________________________________________________

SHARE YOUR KNOWLEDGE—BEGINNERSHave students complete this section if you used the beginners’ differentiation information, or challenge them to find the answers to these

questions at home and discuss how these terms relate to the experiment in class the next day.

1. Define the following key term. Then, provide an example of it by writing the example or drawing/pasting an image

of the example.


Fluid Any substance made up of particles that flow or move freely,such as a liquid or gas.

When you add salt to the water-soaked polymer, the water

molecules diffuse back out of the polymer.

Answer 1: Valid because the data support my hypothesis.

Answer 2: Invalid because the data do not support my hypothesis. I would reject my hypothesis and could form a new one, such as …

Super-absorbent polymers have been used in spill-control

sheets, as water-retention objects for supplying water to plants, in filtration applications, and in medical waste solidification.

If you put a drop of food coloring into a cup of water, the dye particles will eventually spread

throughout the water. Likewise, you can smell food cooking in a kitchen from other rooms because of diffusion.

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LESSON 11: Diaper Polymers