The science of water lab activities: Student directions Name________________________________ P._____ Lab Part A Purpose: The purpose of this lab is to investigate the property of the surface tension of water. This lab will look at the way water sticks to itself to make a rounded shape, the way that water behaves as a “skin” at the surface” and a comparison of water’s surface tension with two other liquids, oil and soapy water. Safety precautions: Do not eat or drink anything in the lab Wear long hair tied back Clean spills immediately * Iodine is an eye irritant/ poison if ingested Materials: -1 penny – use the same penny for all trials to keep results constant. - water - small containers of water, oil, and soapy water - A dropper for each container - a square of wax paper -Stirring apparatus (a spoon, a coffee stirrer, etc. you will get instruction on this) Procedures: Counting drops on a penny 1. Check to make sure you have the needed lab materials at your station 2. Using a dropper containing only water, count the number of drops of water that you can balance on top of a penny. When the water falls off the penny, record the number of drops. Wipe the water off the penny. 3. Repeat the procedure with oil and then soapy water. YOU MUST WASH THE PENNY WITH SOAPY WATER AT YOUR SINK. Complete this washing after trial 2 (oil) AND trial 3 (soapy water) 4. Dry the penny Drops of water on a penny Water Oil Soapy Water Number of Drops Questions: 1) What does a high surface tension do to the number of liquid molecules that can stay together? 2) Based on your evidence, compare the surface tension of these three substances Procedure: Place 3 drops of each liquid (water, oil, and soapy water) onto a piece of wax paper. After placing a few drops of each of the liquids on the wax paper, draw the drops as you would see them from a side view (eye level view). Be sure to capture the relative height/ flatness of each drop Water Drawings Oil Soapy water Procedure: observing surface tension: The surface tension of water is extremely hard to break. Fill the plastic cup to the top so that the water is barely above the top of the cup without spilling over. Get down to eye level. KEEP THE CUP IN THE SINK WHILE YOU DO THIS. Otherwise, you will make a mess on your table. 1. Use a paper clip to observe surface tension 2. Place a paper clip on the surface of the water. Can you get it to float? You may need to try several times. 3. Gently tap the paper clip with a thin object, like the end of a pencil. Observations: Part B: Now you see it, Now you don’t: A dissolving lab Purpose: the purpose of this activity is to introduce the idea that different types of liquids may dissolve different substances. Materials: 3 plastic cups with oil (already poured for you) 1 empty plastic cup Water (from the sink) Granulated salt Granulated sugar Iodine crystals (teacher has them, let them know when you need them) Procedure: Trial 1 1. Fill empty plastic cup ½ full with water 2. Gather 3 cups with oil already poured for you 3. Put about a half-teaspoon of salt into the cup with water 4. Put about a half-teaspoon of salt in one of the oil cups 5. Stir for about 20 seconds 6. Observe- record in the table below 7. Rinse the water cup thoroughly with water…. See step 8 on next page 8. pour the oil into the trash can, rinse with water, wipe out with a paper towel and RETURN the used oil cup to the station where you picked it up. I need to re-use this cup Trial 2 9. fill the empty plastic cup ½ full with water 10. Put about a half-teaspoon of sugar into the cup with water 11. Take the second oil cup, also place about a half-teaspoon of sugar in to the oil 12. Stir for about 20 seconds 13. Observe – record in the table below 14. Rinse the water cup thoroughly with water 15. Pour the oil into the trash can, rinse with water, wipe out with a paper towel and RETURN the used oil cup to the station where you picked it up. I need to re-use this cup Trial 3 16. fill the empty plastic cup ½ full with water 17. Put about a half-teaspoon of iodine crystals into the cup with water 18. Take the second oil cup, also place about a half-teaspoon of iodine crystals in to the oil 19. Stir for about 20 seconds 20. Observe- record in table below 21. Rinse the water cup thoroughly with water, its ok if the iodine is washed down the sink 22. THROW AWAY the cup with iodine and oil. This cup is too hard to clean, we will just get rid of it. Please place it in the trash can. A solvent is the liquid that is doing the dissolving. A solute is the substance that will be dissolved in the liquid. Record your observations about how quickly and thoroughly each of the solutes dissolves in water and oil in the table below Solvent Salt Solutes Sugar Iodine Crystals Water Oil Conclusion: Part a & b: There is a saying “likes dissolve likes”. a) Go back to your table above and label each substance in the table as Polar or Non Polar. Hint: Water is polar b) Summarize what you found in your experiment, based on your recorded observations:
