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Experiment. (NCW/SNC News).

Do you have a simple experiment you would like to share? Experiments will be posted on the NCW webpage to assist NCW coordinators in finding simple experiments for their outreach chemistry shows. Here is an experiment that can be done at schools, in malls or at other outreach events for young children courtesy of John Wiley & Son's Inc. (from 202 Oozing, Bubbling, Dripping & Boucing Experiments by Janice VanCleave, 1996).

Beads and Spreader

Purpose:

To demonstrate surface tension on certain surfaces.

Materials:

2 saucers

Baby powder

Food colouring in a dropper bottle

Dishwashing Liquid

Toothpick

Procedure 1

1) Cover one saucer with a thin layer of baby powder.

2) Place several drops of food colouring on the powder layer.

Results:

The food colouring forms coloured balls on the powder's surface.

What's going on?

Food colouring is coloured water. Water forms beads on certain surfaces because of the surface tension of liquids. Surface tension is the tendency of molecules to cling together at the surface of a liquid to form a skin-like film. The surface molecules tend to pull inward on each other to form a sphere. This occurs when water molecules are more attracted to each other than to the surface they touch.

Procedure 2

1) Pour a drop of dishwashing liquid into the other saucer.

2) Dip the end of a toothpick into the drop of dishwashing liquid.

3) Touch the wet end of the toothpick to several of the coloured beads on the powder.

Results:

The beads break open and spread out

What's going on?

The detergent molecules in the dishwashing liquid move between the water molecules that make up the surface of the coloured beads. The presence of the detergent molecules decreases the strong attractive forces between the water molecules. Thus, the surface tension of the water decreases, and the beads break apart.
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Publication:Canadian Chemical News
Date:Jun 1, 2003
Words:305
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