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This week's LabZone activity
Dec. 7, 2005
Ghosts in the Bathroom
Leave secret messages on your medicine cabinet mirror and learn more about surface tension, soaps, detergents, and humidity.
Description:
A steamy bathroom reveals the handwriting of ghosts on the bathroom mirror.
You Will Need:
- small container of water
- soap or detergent
- cotton swab
Instructions:
Dissolve one or two drops of detergent or a tiny bit of soap in some clean water. Moisten the end of a cotton swab with the solution.
Using the swab, write a secret message on a mirror or other large glass surface. Allow the message to dry.
Once the water has evaporated, a very thin layer of soap remains on the surface of the glass. If too much soap was used in the solution the dry message will be detectable. If that is the case, wash the glass and repeat with a less concentrated solution.
Likewise, if too little soap is used, the message will not appear in the steamy bathroom. Test your solution before attempting to confound your message recipient.
Allowing plenty of time for it to dry, the message should be written on the bathroom mirror prior to the family's routine schedule for bathing and showers. When a family member enters the bathroom, the mirror should appear normal. After a steamy bath or shower, each family member will step in front of the mirror to find a message written to him or her.
There might be a cry through the house, "Who sneaked into the bathroom and wrote this message while I was in the shower?"
Content:
The polar nature of water molecules causes them to be attracted to each other. In a steamy bathroom, water vapor suspended in air collects to form small droplets. Adhesive attraction between water and glass causes those droplets to cling to the surface of the mirror, creating the characteristic fogged-over appearance.
Soaps and detergents interfere with the intermolecular attraction between water molecules. Water droplets deposited on regions of the mirror surface previously coated with soap solution collapse and spread over the surface of the glass. This action creates the illusion that someone has used his or her finger to write a message on the fogged-over mirror.
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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