Oct. 19, 2005

Great Salt Golf Ball

Suspend a golf ball in water and explore solubility, density, and buoyancy.

Description:

A density gradient is created and demonstrated with salt water and a golf ball.

You Will Need:

1. 500 ml or larger graduated cylinder
2. kosher or non-iodized pickling salt
3. golf ball
4. distilled water
5. stopper to fit graduate or rubber band and plastic wrap

Instructions:

This activity can require several days to several weeks to complete. Establish a site for the cylinder to remain on display and undisturbed for that length of time.

Creating a clear solution, kosher or pickling salt is best for this activity. Iodized salt can create a cloudy solution, which will affect the experiment. Some tap sources might add minerals, creating a cloudy solution; therefore, distilled water is best.

Fill the cylinder one-fourth to one-third full of salt. Place a clean golf ball on top of the salt. Disturbing the salt and golf ball as little as possible, carefully pour water into the cylinder until it is nearly full.

To prevent evaporation, use a stopper or plastic wrap and rubber bands to seal the mouth of the cylinder.

Do not shake the cylinder. Avoid a hasty dissolution of the salt.

For a short period of time, the ball will remain on top of the salt. As the salt slowly dissolves in the water, the ball will rise in the solution. Over a period of days it will very slowly rise, eventually appearing to be buoyed near the center of the solution cylinder.

Content:

The product of this activity is a good example of a density gradient. Most salts are extremely soluble in water. Ordinary salt water is more dense than pure water. The golf ball sinks in pure water but floats on a concentrated salt solution. Undisturbed, the more dense liquid remains near the bottom of the cylinder. Molecular motion of water molecules aids the dissolving process.

Teacher's Notes

Activity excerpted by permission of the Chemical Educational Foundation (www.chemed.org) from You Be The Chemist. For additional information about these activities and lesson plans, see www.chemed.org/Kit.html.

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