EXPERIMENT 4.3

PURPOSE:

To investigate cohesion and adhesion in water molecules.

MATERIALS:

• Water
• Bowl
• 4 beakers or clear glasses
• Paper towels
• Wax paper
• Pipette or eyedropper
• Straw
• 2 microscope slides
• Metal paper clip (Use a standard-sized paper clip. A big one will probably not work.)
• Toilet paper
• Dish soap
• Vegetable oil
• Toothpicks
• Scissors
• Blue and red food coloring
• Spoon
• Eye protection such as goggles or safety glasses

QUESTIONS:

Do drops of water look different than drops of oil or soapy water? Can drops of water be separated? Can water move against gravity? Can objects denser than water float? Can water act as glue?

HYPOTHESES:

Write your predictions by answering the questions listed above.

PROCEDURE—PART 1, MOVING WATER:

1. Fill one beaker ¾ full of hot tap water. Add a few drops of red food coloring and stir.
2. Fill one beaker ¾ full of cold tap water. Add a few drops of blue food coloring and stir.
3. Place each beaker filled with water next to an empty beaker so they are side by side.
4. Roll two paper towel sheets into tight tubes.
5. Place one end of one paper towel tube in the beaker of hot water and the other end of the tube in the neighboring empty beaker. Make sure the paper towel roll extends at least half-way down in the water. You will need to bend the tube to a U-shape to have it go into the empty beaker. Repeat with the other two beakers. Draw your experimental set-up in the data table and describe what you observe.
6. Leave this set-up alone and complete the other parts of the experiment before coming back to observe again.
7. After completing the other parts of the experiment record your observations on how the water moved in each set of beakers. Was there a difference between the hot and cold beakers?

Part 1 Data:

PROCEDURE—PART 2, WATER DROPS ON WAX PAPER:

8. Place a sheet of wax paper on a flat surface.
9. Using the eyedropper, place several drops of water on the wax paper. Observe the shape of the drops. Draw and describe them in your data table.
10. Touch one of the drops with a dry toothpick. Describe what happens in your data table.
11. Dip a toothpick in water and then touch a drop with the wet toothpick. Push the toothpick through the drop. Describe what happens in your data table.
12. Try to cut a drop in half with a dry toothpick. Describe what happens in your data table.
13. Place two drops of water close to each other on the wax paper. Using a straw, gently blow between the drops to push them together. Describe what happens in your data table.
14. Dip a toothpick in dish soap. Touch one of the water drops with the soapy toothpick. Describe what happens in your data table.

Part 2 Data:

PROCEDURE—PART 3, FLOATING PAPER CLIP:

15. Fill a bowl about half full with water. Let the water settle for a minute.
16. Tear off a small piece of toilet paper (about 1 inch square).
17. Gently place the toilet paper on the surface of the water.
18. Carefully place a paper clip flat on top of the toilet paper.
19. Use a toothpick to carefully push the toilet paper under the water, leaving the paper clip floating on the surface. This may take a few tries. If the paper clip sinks, try again with a new paper clip and toilet paper.
20. Once the paper clip is floating, observe it closely. Draw and describe what you see in your data table.
21. Dip a toothpick in dish soap. Touch the water surface near (but not touching) the paper clip. Describe what happens in your data table.
22. Try the experiment again, but this time add a drop of dish soap to the water before trying to float the paper clip. What happens? Describe your observations in your data table.
23. Empty the bowl and rinse it out.

Part 3 Data:

PROCEDURE—PART 4, WATER GLUE?:

24. In a clean beaker or glass, measure out ¼ cup of water. Mix a few drops of dish soap into the water and stir.
25. With the eyedropper, on a clean section of the wax paper, place one drop of water and one drop of soapy water.
26. Rinse out the eyedropper with tap water. Place one drop of oil next to the drops of water and soapy water. Draw the drops and describe them in your data table.
27. Place a glass microscope slide on a clean section of the sheet of wax paper.
28. Using the eyedropper, place one drop of water on the glass slide. Describe what you see and compare it to the drops on the wax paper.
29. Place a few more drops of water on the glass slide. Then place the second glass slide on top of the first glass slide. Now try to pull (not slide) the glass slides apart. Describe—was it easy or difficult?
30. Clean off the glass slides under warm water and dry with a paper towel.
31. Repeat steps 29 and 30 using drops of soapy water. Record your results.
32. Repeat steps 29 and 30 using drops of oil. Record your results.
33. Go back to Part 1 and make final observations recording them.
34. Clean up and return all material to their proper place.

Part 4 Data:

INTERACTIVE SIMULATION:

Explore the concepts of cohesion, adhesion, and surface tension with these interactive demonstrations.

SUBMIT YOUR RESULTS:

CONCLUSION:

Based on your observations, explain the following:

1. How do water molecules interact with each other (cohesion)?
2. How do water molecules interact with other surfaces (adhesion)?
3. What is surface tension and how did you observe it in this experiment?
4. How does soap affect the properties of water?
5. How do the properties of water compare to oil?
6. Why was water able to move up the paper towel against gravity in Part 1?