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Unique properties la

By Joseph Moore,2014-11-15 10:10
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Unique properties la

Surface Tension of Water

Introduction:

Water is the most valuable and amazing solution! It has characteristics that set it apart

from all others. Water is the only liquid that expands as it freezes. It also defies gravity

through capillary action, and even holds to the other molecules of water despite

tremendous pressure! Today, you will observe the sheer force of the attraction between

the bonds in a water molecule.

Apparatus (per group):

One 4x 4 (40cm high)

One triangular wooden prism (to act as the fulcrum) One 30 x 3cm piece of wood (to act as the balance beam) One 300mL beaker (filled with water)

Materials (per group):

One pudding cup (empty)

150 pennies

One styrofoam cup

Two lengths of string (each 20cm)

One 3x2cm piece of wood

Silly Putty

BBs (approx. 20)

Procedure:

Part 1

Safety: Wear goggles.

1. On a sturdy table, fill the pudding cup with water from the beaker until the pudding cup is almost overflowing. Do not let it overflow, but add water until a curvature of water forms above the rim of the pudding cup. Be careful not to move the table. 2. Answer #1 from the analysis section on the next page.

3. Add pennies to the pudding cup by

placing them at a 45 degree

to the edge of the rim. The coin should enter the pudding cup at its rim.

4. Count the number of pennies that must be added before the surface tension of the water is broken. Record the data in the table below.

5. Repeat this trial several times to ensure the validity of your results.

Clean-up:

1. Carefully pour the water from the pudding cup into the sink.

***Make sure no pennies fall into the sink.

2. Collect all wet pennies and lay them on paper towels on the back table. 3. Place the pudding cup and beaker of water on the back counter.

Data:

Trial Number of Coins Observations

1

2

3

4

5

Analysis:

1. Predict the number of pennies needed to break the surface tension of the water.

Record the prediction here____________________________________ 2. What was the mean value of all trials?___________________________________ 3. How is the prediction different from the data collected in the experiment? ______ ____________________________________________________________________ 4. What forces are at work during surface tension?____________________________ ____________________________________________________________________ 5. What particles cause these forces? Why?_________________________________ ____________________________________________________________________ 6. Name five uses of surface tension. ______________________________________ ____________________________________________________________________

Procedure:

Part 2

Safety: Wear goggles.

1. Place the 4x4 vertically in the center of

2. Place the triangular prism (fulcrum) with

a rectangular face touching the top of the

4x4.

3. Using a writing utensil, gently punch a

hole 2cm below the upper rim of the

Styrofoam cup.

4. Repeat step 3, making the hole directly across from the first hole on the opposite side of the cup.

5. Fish one end of a piece of string through both holes. Tie the two ends together so that a circle is formed.

6. Using a piece of masking tape, attach the other string to the 3x2cm wood piece. Attach the string to the middle of the piece.

7. Tie the other end of the string in a loop so that it can easily hang from the balance beam.

8. Place the 30x3cm piece of wood (balance beam) on the fulcrum. Hold it until a partner can perform step 9.

9. Place the string from the styrofoam cup over one end of the balance beam. Place the string from the 3x2cm wooden piece over the other end of the balance beam. Let both items hang freely.

10. Place a dime-sized amount of silly putty somewhere on the balance beam to enable both the styrofoam cup and the 3x2cm piece to balance each other.

11. On a sturdy table, fill the pudding cup until it is almost overflowing. Do not let it overflow, but add water until a curvature of water

forms above the rim of the pudding cup. Be careful not to move the table.

12. Place the pudding cup full of water below the balance beam, under the side with the 3x2 piece.

13. Place the 3x2 piece on the surface of the water.

14. Begin adding BBs to the styrofoam cup

on the other end of the balance beam until

the 3x2 piece lifts off the surface of the

water. Count the BBs as they are added.

15. Record the number of BBs needed to lift

the 3x2 piece off the surface of the water.

16. Repeat this trial several times to ensure

Clean-up:

1. Carefully pour the water from the pudding cup into the sink.

2. Place the pudding cup on the back counter.

3. Place BBs in their proper container.

4. Place all other materials in their designated locations on the back table.

Data:

Trial Number of BBs Observations

1

2

3

4

Analysis:

1. On average, how many BBs were needed to overcome the force of attraction between the water and the 3x2cm piece of wood?_____________________________ _____________________________________________________________________ 2. Why is the piece of wood attracted to the surface of the water?_________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ 3. How is the term “cohesion” related to what you observed during this lab? _______

_____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________

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