Where's the Water?

Purpose:

To show how absorbent sodium polyacrylate is; it can absorb as much as 100 to 1000 times its mass in water.

Materials:

• 100mL beaker
• 3 styrofoam (or similar) cups

Reagents:

• Sodium polyacrylate

Hazards and PPE:

• Sodium polyacrylate forms a highly absorbent gel on contact with water. As such, it is very dangerous to ingest or inhale. Avoid doing so.
• Wear approved safety goggles and gloves.

Protocol:

Preparation

1. Place 3g sodium polyacrylate into one opaque cup and into 100mL beaker.
   1. Do this out of view or before demo.

Demonstration

1. Line all 3 opaque cups up in front of audience.
2. Add ~15-20mL DI water to the cup containing the solid sodium polyacrylate, until the surface of the solid is covered.
3. Shuffle cups, similar to a shell game, and encourage audience to attempt to keep track of the cup containing the water.
4. Ask audience to identify the cup with the water.
   1. Invert each cup as it is guessed.
5. Reveal 100mL beaker containing solid sodium polyacrylate.
6. Add 15-20mL water to beaker in full view of audience to demonstrate absorption of water by sodium polyacrylate.

Additional Notes:

• Sodium polyacrylate's absorbency is not just cool, it's also useful! It is the same substance that is used in diapers.

Disposal:

• Both solid and gelled/hydrated sodium polyacrylate may be disposed of in landfill trash. It should not go down the sink.

Reactions:

• I have not been able to find this reaction in any documentation I have available. If you have this reaction, please feel free to share it!

Citations:

1. This demo adapted from the demo library of the Chemistry department at the University of Illinois at Urbana-Champaign.
2. Flinn Scientific.

Videos:

• Three Cup Sodium Polyacrylate

  Jmu ChemDemos