Properties of Water
Name: _________________
Date:
Introduction:
Water molecules are polar (have a positive and negative end). The polarity of water allows
it to be attracted to other water molecules via hydrogen bonds.
(See figure). Beneath the surface of water, molecules are attracted to each other from all
directions. Because of this attraction, molecules do not have a tendency to be pulled in any
specific direction. However, water molecules at the surface bond only to molecules next to
and below them (because there are no water molecules above them). This type of
interaction at the surface results in the formation of a kind of elastic layer/barrier. Surface
tension is what allows objects such as needles, razor blades, water bugs, and pepper to
float on the surface of liquids.
For ALL stations described below, make OBSERVATIONS first then EXPLAIN them in terms of the chemical composition of
the water molecules. At some stations, you will be asked for the biological importance of the phenomenon. Use words
like hydrogen bonds, polarity, unequal sharing of electrons, cohesion, adhesion, solvent, conductivity, ions etc.
(2 points/station)
Station 1: Paper clips/
1a. Fill a cup or beaker with water and rest a paper clip/ on the surface. This may take some practice!
Observations:
Explanation:
Biological Significance:
1b. Put a drop of dish soap on your finger and into the water. Put it in somewhere near the floating paper clip
Observations:
Explanation:
Station 2: Pennies!
2a. Using a plastic pipette, fit as many drops of water on the surface of a penny as you can.
Prediction: How many drops of water do you think will fit on the penny?_______________
Observations:
Explanation:
2b. Using a plastic pipette, fit as many drops of oil on the surface of a penny as you can.
Observations:
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Properties of Water
Name: _________________
Date:
Explanation:
Station 3: Walking water
1.
Position your three empty beakers about 2 inches apart.
2.
Step 2 – Add a few drops of food coloring into the water.
3.
Step 3 – Stir the food coloring until the water is all one color.
Step 4 – Cut a paper towel in half and then fold it into quarters lengthwise. Stick one end of the paper towel into the
colored water and one end into the other beaker of colored water. Do the same for the third
4.
Observations:
Explanation:
Biological significance:
Station 4: Pepper
Fill a cup or beaker with water and sprinkle pepper on the surface of the water. Make sure there is enough pepper to coat the layer
of water. (5-10 sprinkles).
4a. With clean hands, touch the water lightly with a fingertip.
Observations:
Explanation:
4b. Put a small drop of liquid soap on your fingertip and touch the surface again.
Observations:
Explanation:
Station 5: balloon and water
5.
Rub the inflated balloon vigorously on something wooly or on your head, open the tap so that you have a sloe, steady
stream of water, place the balloon r close to the stream of water.
Observations:
Explanation:
Station 6 : Graduated cylinder
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Properties of Water
6.
Name: _________________
Date:
Fill the graduated cylinders with water to a certain level. Observe the top of the water column.
Observations:
Explanation:
Station 7 : Glass slides
7.
Put two drops of water on a slide and put the other slide on top. Try to separate them.
Observations:
Explanation:
Biological Significance:
Station 8: Water, salt and a lightbulb
8.
Insert the electrodes of the lightbulb in the beakers filled with water. Observe.
Then put some salt in one of the beakers with water, stir well and insert the electrodes in the water. Observe.
Observations:
Explanation:
Biological significance:
Station 9: string and Tap
9.
At this station you will find a rope attached to a tap, which is slightly opened.
Observations:
Explanation:
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Properties of Water
Name: _________________
Date:
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Properties of Water
Name: _________________
Date:
Post lab questions: Answers MUST be typed and handed in individually.
1. Describe the biological importance of the phenomena observed in Station 1, 3, 7, and 8.
/4
2. Soap molecules have a polar and non-polar region. The polar region of soap is attracted to water and will bond
with water, and the non-polar end is attracted to grease and dirt. Given this information and your observations,
hypothesize how the soap affects the surface tension of water.
/2
3. How would you design an experiment to test whether the temperature of water has any effect on surface
tension? Be sure to indicate what your dependent and independent variables would be.
/2
4. Based on the experiment designed in question 3, predict how the surface tension of water would change with
increasing temperature. Explain your prediction.
/2
5. Hypothesize why the pepper moved after soap was added to the cup of water.
/2
6. Based on your observations at the pennies station, would you predict that oil has stronger or weaker attractions
between its molecules, compared to water?
Explain.
/2
7. Explain how water striders and some lizards can walk on water. What property of water is responsible for this?
Explain the chemical cause of this property. What station shows this property?
/2
8. The lungs have no muscles to help them expand. How then do they expand? There are two membranes
surrounding the lungs, called the pleural membranes. The outer one lines the inside of the chest cavity, the
inner one lines the lungs. The two membranes are separated by a thin film of watery fluid. When the chest
cavity expands, the lungs expand also. Which station shows this principle?
/2
TOTAL: 36 pts.
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