Bending Water

 

DESCRIPTION:
When the balloon is rubbed on a pair of jeans, electrons are wiped from the jeans to the balloon, causing a net negative charge on the balloon. The charged balloon is held near a thin stream of water. Charges in the water rearrange so that the positive charges in the water become attracted to the negatively charged balloon, and the stream of water bends. The rearranging of charges is pronounced because water is a polar molecule.

TOPICS COVERED:
polarity
physical change
charging by friction
charging by induction

MATERIALS NEEDED:
– buret w/ stand
– colored water (makes it easier to see)
– beaker
– balloon

PROCEDURE:
1. Fill the buret with the colored water
2. Charge the balloon by rubbing it on jeans, or a kimwipe
3. With a beaker under the buret, have a slow but steady stream coming from the buret
4. Hold the balloon next to the stream of water to pull it sideways

ADDITIONAL COMMENTS:
When the water is pulled sideways it can overshoot the beaker, causing a mess. A large beaker or a large amount of paper towels can make this demo less of a cleanup.

SAFETY:
Safety goggles should be worn at all times.

REFERENCES:
Shakhashiri, B.Z. Chemical Demonstrations;  University of Wisconsin Press: Madison, 1989; Vol. 3, pp 329 – 332.

STORY:
This could be tied into water’s bent Lewis structure as a play on words. 

Handout

This inquiry style lesson plan focuses on intermolecular forces. After using Bending Water to review polarity, students do a lab with 4 solvents, learn about London dispersion forces, dipole-dipole interactions, and hydrogen bonding, and draw intermolecular interactions.