Does Soap Affect the Surface Tension of Water?
Surface tension refers to water's ability to "stick to itself". Surface tensioncan be measured and observed by dropping water (drop by drop) onto a penny. Thenumber of water drops that can fit on a penny will surprise you.
How does soap affect the water’s surface tension?
I think that the surface tension of soapy water will be less than that of freshwater because H
0 has strong polar bonds, and when water is mixed with soap the polar bonds which help to bind the water together are weakened, thus lessening the surfacetension.
pipette, liquid soap, water, beakers, penny, graduated cylinder, ...view middle of the document...
Ask students if they have ever seen a water strider sitting on the surface of a pond. The water molecules stick together and form a "skin" on the surface strong enough to hold up the insect. This is an example of surface tension, the ability of a liquid to stick to itself. Surface tension may be affected by adding soap to the water, and the effect can be measured by comparing the number of drops of plain tap water versus the number of drops of soapy water that stick to a penny. If soap increases the surface tension, more drops of soapy water than tap water will stick to the penny, whereas if soap decreases the surface tension, fewer drops of soapy water will stick. Students will employ the scientific method by developing a hypothesis, testing the hypothesis by collecting and analyzing data, and drawing a conclusion.
• Eye droppers
• Liquid dish detergent
• Plastic cups for water
• Paper towels
Add some dishwashing detergent to 2 or 3 liters of water ahead of time and mix thoroughly, so that there is enough for all the groups to use the same batch. Label the plastic cups "Tap" and "Soapy" so that students don't get them mixed up. These cups can be reused for multiple classes. Have separate eye droppers for the tap and soapy water so that no soap gets into the tap water.
Activities for Classrooms
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Divide students into groups. Each group will place a penny on top of a paper towel on the table or lab bench, making sure that it is flat. One student will carefully drop tap water onto the surface of the penny, while the others in the group help to count the drops and record the data. It is surprising how many drops the penny will hold before the water begins to run off! They will repeat this four times with tap water, and four times with soapy water, drying the penny off between trials. All of the...