Station 1. Polarity of Water

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Fay Audra Merritt
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1 Station 1 Polarity of Water As we learned last week, water is a polar molecule meaning it has one end with a slight positive charge and another end with a slight negative charge. Molecules without slight charges on either end are nonpolar. As a general rule, water is good at dissolving polar and ionic compounds. 1. Fill a beaker 1/3 of the way with water. 2. Add two drops of food coloring to it. Allow the water to become uniform before moving on to the next step. 3. Add a small amount of cooking oil to the beaker of water. 4. Record your observations on your data sheet. 5. Empty the contents of your beaker into the sink and clean the interior of the beaker (BE CAREFUL OF THE WATER PRESSURE!) 6. Using the same beaker (which should now be clean), fill the beaker 1/3 of the way with water. 7. Add a pinch of salt to the beaker. 8. Record your observations on the data sheet. 9. Rinse the contents of the beaker and dry the beaker in preparation for the next group. 10. Respond to the questions on your answer sheet.

2 Station 2 Water as a Catalyst Water is needed for most chemical reactions that take place within living organisms, like us. 1. In a clean, dry beaker, add a small amount of baking soda. Then add a small amount of cream of tartar. 2. Record what happens on your answer sheet. 3. Measure out 20 ml of water with your graduated cylinder. 4. Now SLOWLY add water to the mixture. 5. Record what happened on your answer sheet. 6. Pour the contents of the beaker down the sink. Clean and dry the beaker for the next group. 7. Respond to the questions on the answer sheet.

3 Station 3 Surface Tension & Cohesion Water molecules are attracted to each other because of their polarity. The positive and negative ends attract to one another like magnets. This attraction is called cohesion which allows the molecules to stick together. At the surface, this produces a film that covers the surface and holds it. This film is called surface tension. 1. Fill the beaker nearly to the top with water. 2. Obtain a paper clip. 3. Try to balance one of the paper clips on top of the water so it appears to be floating. 4. Once you have it balanced, give it a slight push. Record your observations on your answer sheet. 5. Again, balance the paper clip on the top of the water. This time, add a drop of mild detergent. Record what happens on your answer sheet. 6. Clean the beaker and paper clip so there is no detergent remaining. Dry the beaker and paper clip and set up for the next group. 7. Respond to the questions on your answer sheet.

4 Station 4 Surface Tension & Cohesion Again Water molecules are attracted to each other because of their polarity. The positive and negative ends attract to one another like magnets. This attraction is called cohesion which allows the molecules to stick together. At the surface, this produces a film that covers the surface and holds it. This film is called surface tension. 1. Obtain a penny and a pipette. 2. Use the beaker of water on the lab table to fill the pipette. 3. Lay the penny flat on the table. 4. Add as many drops of water as you can to the top of the penny. Record the number of drops you can put on the penny before it overflows on your answer sheet. 5. On your answer sheet, draw what the penny looks like, as viewed from the side, before it overflowed. 6. Clean up any spills that occurred and dry the penny so it is ready for the next group. 7. Respond to the questions on your answer sheet.

5 Station 5 Cohesion & Adhesion When water sticks to something, we call this adhesion. When you step out of the shower and see tiny droplets of water on your skin this is an example of adhesion. In a plant, cohesion and adhesion help the plant by allowing water to travel upwards away from the roots to deliver water to all parts of the plant. 1. Fill a beaker nearly to the top with water. 2. Add 3-4 drops of food coloring to the beaker of water and wait for it to become uniform in color. 3. Place the end of the capillary tube into the beaker of water and CAREFULLY move it up and down. 4. Observe and record what happens to your answer sheet. 5. GENTLY & CAREFULLY rinse the capillary tube and beaker, and set up for the next group.

6 Station 6 Solutions & ph When water is mixed with most other substances, it turns into a solution. When dissolved, some substances may increase or decrease the amount of hydrogen ions found in the water. Substances that increase the number are called acids and ones that decrease the amount are called bases. 1. Obtain 5 ph strips. 2. Using just the end of the ph strip, dip into beaker #1. 3. Wait 30 seconds before recording the ph reading on your answer sheet. 4. Repeat steps 2-3 for each beaker with a new ph strip for each. Don t forget to record the ph reading for each beaker! 5. Determine which substance was the most acidic and most basic. 6. Using a graduated cylinder, measure 5 ml of the most acidic and pour into the empty beaker 7. Rinse the graduated cylinder. 8. Using the same, rinsed graduated cylinder, measure 5 ml of the most basic substance and pour into the beaker with the most acidic. 9. Swirl the beaker gently to mix the two together. Using the last ph strip, test and record the ph. 10. Dump the contents of the beaker into the sink. Rinse and dry. 11. Set up the area for the next group. 12. Respond to the questions on your answer sheet.

7 Properties of Water Station Lab Station 1: Observations of Water & Oil Observations of Water & Salt 1. Based on your observations, which substance is non-polar? Make sure to explain your answer in complete sentences! Station 2: Observations of Baking Soda & Cream of Tartar Observations after adding Water 1. Using your observations as evidence, explain why water is needed for this chemical reaction to take place? Station 3: Observations after pushing Paperclip Observations of Paperclip & Detergent 1. When placing the paperclip into the water, did it float? Was it difficult? Easy? Explain. (Hint: think of hydrogen bonds) 2. Why do you think the paperclip reacted the way it did when detergent was added? Explain your reasoning.

8 Station 4: # of drops Drawing of Penny (side view) 1. Explain why the penny was able to hold so many drops? 2. In your opinion, what caused the water to spill over? Station 5: Observations 1. What evidence of adhesion and cohesion could be observed with the capillary tube? Station 6: Beaker #1 Beaker #2 Beaker #3 Beaker #4 1. What happened to the ph when you mixed an acid and a base together? In your opinion why did this happen? 2. The solution in Beaker #4 is a Tums solution. Using your ph readings, why do you think we take Tums when we have an upset stomach?

Surface Tension and Adhesion

Surface Tension and Adhesion 1. Obtain a medicine dropper and a small graduated cylinder. Make sure the dropper is clean. 2. Drop water into the graduated cylinder with the dropper, counting each drop.