Biology Lab for virtual school.. Lesson 1.04

Categories: BiologySchoolWater
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When an object falls onto the surface, it has to push the water molecules apart. If the effect of the weight of the object is insufficient to match the attractive forces between molecules in the surface layer, the object will not enter the surface.

Molecules of most detergents and soaps are long chain hydrocarbon molecules with an ionic group at one end, usually carrying a negative charge, thus making it an anion.

When the drop of detergent is added to the powdered surface, the initial effect is to draw the powder back to the edges very rapidly as the detergent molecules form their own surface layer with a lower surface tension than the water.

As the detergent gradually mixes with the water, the powder begins to sink, and a needle will now pass through the surface with ease under its own weight. However, the calcium and magnesium salts of many detergent molecules are soluble, so detergents still lower the surface tension of hard water


If you add soap to water, than it will decrease the effect on the surface tension.


Control: Is the tap water
Independent Variable: Is the soap
Dependent Variable: Is the drops of soap you fit on the penny

1. I received a beaker filled with tap water.
2. I took a pipette and filled it up with water from the beaker. 3. I began to add drops of water to a penny, which was heads up, every one second from a height of ½ centimeter and counting how many drops I had put on it.

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4. After I added the drop that caused the water to flow over, I recorded how many drops stayed on the penny, and I then dried the penny with a paper towel. 5. I repeated steps two through four, four times.

6. I took 100 ml of water and poured it into a beaker.
7. I got 3 ml of soap.
8. I added the 3 ml of soap to the beaker and stirred the solution 40-50 times with a fresh pipette. 9. I filled the pipette with the soapy water solution and began to start adding drops of the solution to the same penny, from the distance of ½ centimeter, at a rate of one drop per second. 10. After adding the drop that caused the soapy water to flow over, I recorded how many drops stayed on the penny, and I washed the penny under running Water And dried it with a paper towel. 11. I repeated steps nine and ten, four more times.


The soap is thick and the penny is rough. The tap water latest longer than
the soapy water


Drops of Tap and Soapy Water Added to a Penny
Trail 1 Trail 2 Trail 3 Trail 4 Trail 5 Average
Drops of Tap Water 35 28 11 15 39 25.5 Drops of Soapy Water 20 16 11 26 15 1.3

I got my average from using Microsoft Excel


I have accepted my hypothesis because of the results of the data from this lab. In my hypothesis I stated that the surface tension of the tap water is higher than that of soapy water. My data supports this hypothesis because the average drops of tap water the penny could hold was 25.5 while the average drops of soapy water was 17.3 drops.

This shows that soapy water has a lower surface tension, thus making it not able to hold as many drops of soapy water could on the penny. I noticed in my data that in trials 3 and 4 that the penny held more drops of soapy water than tap water. This was not in accord with my hypothesis, and I think it may have been due to a weakness in the experiment. When I used the pipette to suction water and then drop it onto the penny may not have been doing it exactly the same way each time. All in all, my experiment conducted that my hypothesis was correct


This relates back to the way soapy water and tap water act in everyday situations. The soap causes the surface tension to be less than that of water so if you poured soapy water onto a kitchen counter the solution would disperse as broadly as it could over the entire counter. Tap water on the other hand when spilled on a counter will naturally try to come together in water colonies. The molecule sin the tap water will move towards each other and stack on top of each other thus leaving some parts of the counter dry and some parts with canals of water.

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Biology Lab for virtual school.. Lesson 1.04. (2016, May 18). Retrieved from

Biology Lab for virtual school.. Lesson 1.04

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