Science Activity
#11 - Where's the Water?
All experiments must be done in the presence of a parent or teacher.
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Ideas
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Key Words
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Materials
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Procedure
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Observations
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Summary
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Questions
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WWW Links

Ideas to be Developed

Sodium polyacrylate powder, a super absorbent polymer. Sodium polyacrylate is a polymer, meaning that it consists of chains of identical units, known as monomers.

- CH2-CH(COONa) -

When water is added to the white crystalline polymer, they absorb many times their size and a polymeric gel forms. In the absorbing process, the gel that forms swells.

Exactly how much water does this polymer absorb? Make your prediction below.

Disposable diapers use small amounts of sodium polyacrylate to absorb baby urine. The more polymer powder in a diaper, the more urine it can absorb.

In addition to its use in disposable diapers, sodium polyacrylate, have many uses.

  1. It is found in soil to help soil retain water.
  2. It is used by florists as a dirt-free way to store water and to keep cut flowers fresh for a long time.
  3. It is used in filtration units that remove water from airplane and automobile fuels such that vehicles perform more efficiently.
  4. It is used to make Gro-Creatures, which are toys shaped like dinosaurs, fish, lizards, and other assorted animals that increase in size when placed in water. These critters can be dried out and rehydrated over and over again.

When the sodium polyacrylate is immersed in water, there is a higher concentration of water outside the polymer. When water approaches a sodium polyacrylate molecule it is "drawn" to the center of the molecule by osmosis. The ability of the polymer to absorb excessive amounts of water is due to osmotic pressure (the movement of water through a membrane permeable only to water). The sodium polyacrylate absorbs water until there is an equal concentration of water inside and outside.

Safety Considerations:
Students who have alllergies, especially allergy to disposable diapers should be an observer or recorder for the group. Sodium polyacrylate is non-toxic! However, if placed in the eye, the eye will become dry and irritated. Inhalation of the powder will also be irritating to nasal membranes. Be careful, and minimize exposure to sodium polyacrylate. Dispose of excess powder and/or gelled material in the trash. Do not put down the sink!


Key Words

polymer - A large, usually chainlike molecule that is made up of chains of identical units that repeat itself. In sodium polyacrylate, the repeating unit is -CH2-CH(COONa)-

osmosis - Osmosis is the movement of water across a semi-permeable membrane from areas of low solute concentration to areas of high solute concentration.


Materials Required

6 - 7 baby diapers
6 - 7 large garbage bags


Procedure

TEACHER DEMO -
The lizard is a Gro-Creature.

The photo shows that it is 16 cm in length.

Make your prediction:
What percent of change will the lizard experience?
I. Dissect a diaper:

  1. Divide the class into groups of 4 and use scissors to carefully cut open the inside of a diaper lengthwise.
  2. Transfer the diaper inside a large garbage bag, peel back its outer lining. Pull the filling out of the diaper into the bag. Discard the outer lining.
  3. Reach into the garbage bag and shred the filling into small bits. This will help to loosen the granules of polymer from the
  4. Hold the bag shut and shake vigorously. Repeat three to four times, then discard the filling.
  5. Shake the granules into a corner of the bag. Cut off the corner and empty the granules into a clear plastic cup.

II. Make your prediction: How much water does this polymer absorb?

III. Test your prediction:

  1. Add 50 mL of water into the clear plastic cup containing the granules of sodium polyacrylate. Record observations and detailed descriptions of what's happening in the cup.
  2. Using the graduated cylinders, ask students to measure 10ml of water. Pour the water into the plastic cup with the sodium polyacrylate. Have students record results with 10 ml of water added.
  3. Repeat step 2, always recording observations and measured amounts. Continue adding water to determine how much water can be absorbed by the sodium polyacrylate.


Observations

Make your predictions:

I predict that the final length of the lizard is

___________________________________ cm

I predict that the amount of polymer that I recovered from the diaper will absorb

___________________________________ mL of water

Observations:

1. What do these granules of sodium polyacrylate look like?

 

 

 

2. Record your observation:

Amount of water added to the sodium polyacylate
Observations
50 mL
 
100 mL
 
110 mL
 
120 mL
 
130 mL
 
140 mL
 
150 mL
 
160 mL
 
170 mL
 
180 mL
 
190 mL
 
200 mL
 
- add to this table if you need to -


Summary
Summarize your findings and comment on your prediction and the outcome of this experiment.

Questions

1. In addition to its use in disposable diapers, can you think of some other uses for sodium polyacrylate?

 

 

 

 

2. Do you think the invention of the disposable diaper is a good thing? List some pros and cons for using disposable diapers over cloth diapers for a baby. Draw your conclusion of which type of diaper you would recommend.

 

 

 

 


WWW Links

The Ability of Sodium Polyacrylate to Absorb Water at the How Stuff Works Site
Diaper and Super Absorbant Polymers (lots of good links to other related links here)
Polymer Chemistry and "Diapers"
FAQs on What diapers to use
Cloth vs. Disposable


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Ideas
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Key Words
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Materials
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Procedure
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Observations
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Summary
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Questions
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WWW Links

Howard Debeck Elementary School
8600 Ash Street Richmond, B.C. V6Y 1S2
Phone: 604-668-6281 - Fax: 604-668-6004


Richmond School District Homepage