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# BIOLOGY PENNY LAB

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BIOLOGY PENNY LAB

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### BIOLOGY PENNY LAB

1. 1. PENNY LAB Introduction: Surface tension refers to water’s ability to “stick to itself”. Surface tension can be measured and observed by dropping water (drop by drop) onto a penny. The number of water drops that can fit on a penny will surprise you. Part A: Perform a CONTROL test for comparison with later results. 1. Make a guess about how many you think will fit on a penny. _________________ 2. Hypothesis: I think a penny will hold ________________ drops of water. 3. Materials: Penny, Eyedropper , tap Water, soapy water, paper towel, forceps 4. Procedure: 1. Put the penny on a flat surface. 2. Use the eye dropper to drop water on the penny, one drop at a time. 3. Count the number of drops until the water spills over the edge of the penny. 4. Record your data. 5. Repeat steps 1 -4 for a total of 5 trials. Sometimes a steady hand can make more drops fit on the penny. A bump of the table can reduce the drops. We should do a few tests to get an average to see how many drops fit on a penny. Test 1 Test 2 Test 3 Test 4 Test 5 AVERAGE Tap water Part B: Perform tests with the TESTING LIQUID. Question: How does soap affect the water’s surface tension? 5. Develop a hypothesis. (underline the word that you think is correct) Soap will [ increase /decrease ] the surface tension of the water. 6. Make a prediction. Choose the one below that matches your hypothesis a. Soap will increase the surface tension, therefore I will be able to place more drops on the penny b. Soap will decrease the surface tension, therefore I will be able to place less drops on the penny Names _____________________________________________________ DATE:________________________________
2. 2. 7. Test your hypothesis by comparing the number of drops of tap water to the number of drops of soapy water that can fit on a penny. Because water drops may vary depending on how well you drop the water, it is best to run many trials and take an average. Record your data in the table below Step 1: Start with a “clean” penny. Rinse the penny in tap water and dry completely. Be sure to remove as much residue as possible - Step 2: Place penny on dry spot on a paper towel. Place drops of SOAPY WATER on the penny (one at a time) until ANY amount of water runs over the edge of the penny. Step 4: Record your observations and the number of drops for that trial in the table. Repeat Steps 1 - 5 three more times before calculating the average. Test 1 Test 2 Test 3 Test 4 Test 5 Average Soapy Water 8. Draw Conclusions: Was your hypothesis correct? ______________ Complete this statement now that you know the facts Soapy water will [increase / decrease] the surface tension of water. You should be able to place [ more / less ] drops of soapy water than you can tap water. 9. Communication: An important part of science is comparing your results to others. Check the groups near yours. Did they get the same results? __________ 10• Why did we perform more than one trial? 11. What benefits are there to repeated trials? 12. • What could we have done to make sure all the groups ended up with similar results? 13. • What is the control for this experiment? 14. What is the independent variable? 15. What is the dependent variable?
3. 3. Drops On A Penny Lab Cohesion Water molecules are attracted to other water molecules. The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is what gives water its cohesive properties. Surface Tension Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. The cohesion of water molecules forms a surface "film" or “skin.” Some substances may reduce the cohesive force of water, which will reduce the strength of the surface “skin” of the water. Use this information to help you answer the questions on the lab sheet after you have completed the experiment!
4. 4. Drops On A Penny Lab Fill in with the missing words. Cohesion – Water molecules are _______________ to other water molecules. The _____________ end of water has a _____________ charge and the _____________ end Has a _____________ charge. The hydrogens of one water ______________ are attracted to the oxygen from other water molecules. This attractive __________ is what gives water its_____________ properties. Surface Tension - Surface tension is the name we give to the ______________ of water molecules at the ___________ of a body of ___________. The cohesion of water molecules forms a surface "_________" or “_________.” Some substances may ____________ the cohesive force of water, which will reduce the _______________ of the surface “skin” of the water.
5. 5. 1. Draw the water molecule 2. Illustrate how the molecules are arranged in each State of water Solid Liquid Gas
6. 6. 3. Why are water molecules polar? A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. The unequal sharing of electrons causes the water molecule to be polar. 4. How are cohesion and adhesion similar? Different?