Jason Mertell -Surface Tension

Title: Surface Tension

Principles Investigated: Surface Tension, hydrophobic, and density. The effects of salt, soap, and hot water on surface tension. Mass vs. surface tension.

Standards: 6C: Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.

1:8 Students know properties of solid, liquid, and gaseous substances, such as sugar (C₆HO₆), water (H₂O), helium (He), oxygen (O₂), nitrogen (N₂), and carbon 12dioxide (CO₂).

2E: Students know how sugar, water, and minerals are transported in a vascular plant.

Materials: 30 paper clips, yen, soap, 12 cups, 5 250 mL beakers, hot water, room temperature water, skinny popsickle sticks, milk, 6 (4 packs of food coloring), and 6 paper plates, and q-tips.

Procedure:

1. Initially ask the students which is denser, a paperclip or water? Then place a paperclip into the water to show them the paperclip will sink. Create a “need to know” by using one paperclip to allow another paper clip to sit on top of room temperature water. Make sure to do this behind something so students do not initially see how it is done.

2. Show students from the powerpoint other examples of things that can walk or sit on top of water.

3. Ask students what this property is. (Surface Tension)

4. Get students into groups of 3-4. Give each group 2 large paper clips and one glass of room temperature water. Tell them they can bend the 1^st paperclip any way they would like to get the other paperclip to sit on top of the water without touching the glass at all.

5. Give the students 2-3 minutes to try it themselves. Have them discuss strategies inside their groups on how to make the 2^nd paperclip sit on top of the water.

6. Have a successful group to demonstrate their method in getting the paperclip to sit on top of the water. If they were not successful then demonstrate to them the best way, which is bending one of the paperclip 90 degrees and placing the paper clip on top of the other one so it is parallel to the water thus allowing for the weight to be distributed evenly and not break the surface tension.

7. Have them practice putting the paper clip in using this method so they can use it for the next part of the lab.

8. Now have the students predict what will happen when they put it into hot water or add soap to the water.

9. Have the students put their paperclip into the hot water and see if they are able to get it to float. If the paperclip drops have them use the skinny popsickle stick to fish it out. Then have them put it in the other cup and get it to rest on top of the water then have them add soap and to record in their lab sheet what happened.

10. Discuss the results to why or why not it sank in the various solutions.

11. Have students discuss their results with the rest of the class.

12. Teacher will discuss results using powerpoint. (hot and soapy water results)

13. When discussing the results to the hot water the teacher will show the graph of the hot water and how surface tension is lost as water temperature increases.

14. To explain the soap’s affect on the surface tension have students do the following:

a. Put milk into a dish about 2 mm thick.

b. Put 5 drops of the four different food coloring samples into the middle of the plate.

c. Then using a q-tip, have students dip the q-tip into soap and place it into the middle of the plate.

15.Have the students get the coins and do the coin part of the lab.

16. Finally you can discuss how this knowledge could apply to everyday life.

Questions and Answers:

1. How can a paper clip, which is more dense than water sit on top of water?

2. Does hot water weaken or strengthen surface tension?

3. Does soap break apart or strengthen surface tension?

4. Would you want more or less surface tension for disinfectants?

5. Would you want more or less surface tension when cleaning the dishes?

1. Surface tension is stronger than the force of gravity acting on the mass of the paper clip, which denser than the water.

2. Weaken the surface tension?

3. Break apart the surface tension.

4. Less

5. Less

Students Prior Knowledge: The student will need to understand the basic structure of a water molecule, salt, soap, and what happens to hot water molecules when they are heated. They should also be familiar with mass, gravity, and density.

Applications to everyday life: When washing dishes, the learner will understand that it is better to use hot and soapy since they both reduce the surface tension of water. Antiseptics like dettol have low surface tension, so that they spread faster. In soldering, addition of flux reduces the surface tension of molten tin. Plants being able to get water by surface tension and capillary action. Clinical test for Jaundice( urine with lower surface tension is a sign that bile is present which is an indicator for jaundice. Common tent materials are somewhat rainproof in that the surface tension of water will bridge the pores in the finely woven material. But if you touch the tent with your finger it will break the surface tension of the water and the rain will drip through. This would be good to know if you were designing something rainproof. Disinfectants are usually solutions of low surface tension. This allows them to spread out on the cell wall of the bacteria and disrupt them.

Resources:

Surface Tension http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html Accessed April 1st 2011

Wikipedia (Surface Tension) http://en.wikipedia.org/wiki/Surface_tension Accessed April 20^th 2011

Vision Learning http://www.visionlearning.com/library/module_viewer.php?mid=57 Anthony Carpi, Ph.D. "Water: Properties and Behavior," Visionlearning Vol. CHE-2 (1), 2003.

http://www.visionlearning.com/library/module_viewer.php?mid=57

Name:_________________

Surface Tension Lab

Instructions:

Part A: Use one paperclip to help the other paperclip stay on top of the water by bending it in any way. Do not change the shape of the one you want to lay on top of the water.

Describe how your group tried to get your paperclip to sit on top of the water:

Part B: Predict what will happen when you put the paper clip into the following environments.

I. Hot water:

Predictions:

Outcome:

II. Adding soap to room temperature water:

Predictions:

Outcome:

III. Investigating results from adding soap to the water.

A. Poor milk into paper plate (enough to cover the whole bottom of the plate to a thickness of a couple of mm’s.

B. Take the food coloring and place 5-6 drops close to the middle of the plate. Do this will each color, placing the colors next to each other but not on top of each other.

C. Place the q-tip in the soap. Then Put the q-tip in the middle of the plate with the mild and observe what happens.

Write down your observation:

IV: Coins

1. Try to see if you could rest the following coins on top of the water.

a. yen with finger Y/N

b. yen with paperclip Y/N

c. dime with paperclip Y/N

Explain your results: