Water, Water Everywhere . . .
Extraordinary Properties of Water
___/2-Title
___/10-Introduction: Be sure to include a discussion of the following:
-Why water is so important?
*Discuss water on Earth, in cells, etc
-Discuss how water is formed on the atomic level. Include a diagram.
-Discuss how the molecular structure of water results in a variety of its characteristics.
___/2-Purpose: remember to underline!
___/2-Experimental Design: Give a brief overview of the experiment.
For each of the 6 sections of the lab: bonding, cohesion, adhesion, temperature stability, density and
the heat of vaporization you should have the following:
___/6-Equipment/Apparatus
___/12-Procedure
___/18-Results/Data: Include Labeled diagrams and data tables for each experiment.
___/24-Discussion: respond to the questions in the “Results and Conclusions” section of the lab
handout.
The following portions should be completed after each lab section is finished. You need one section to
summarize the enter lab.
___/4-Conclusion: Summarize findings citing evidence for each conclusion.
___/4-Evaluation: human error, areas that were unclear
___/90+___/10 (name, clean-up, this stapled to the front of lab)=___/100
Extraordinary Properties of Water
Water Lab
Water is the medium that makes life, as we know it, possible here on Earth. Almost threefourths of the Earth’s surface is covered by water. Most cells are surrounded by water; 70% to 95% of
the cell’s internal environment is water. Water is so common we often see it as nothing special. In fact,
it is the makeup of the water molecule and its corresponding unique properties that support life on
Earth. Water is essential to life.
Water if formed by the covalent bonding (sharing of electrons) between an oxygen atom and
two hydrogen atoms. Although the molecule as a whole is electrically neutral, the center of positive
charge does not coincide with the center of the negative charge. The oxygen atom is much more
electronegative that the two hydrogen atoms with which it shares electrons. Oxygen draws the shared
electrons closer to itself, giving the molecule an asymmetric charge; i.e. the oxygen is slightly negative,
each hydrogen slightly positive. This unequal distribution of charge is termed polarity and water is a
polar molecule. It can form hydrogen bonds and “attract itself.” The attraction of the water for itself is
termed cohesion. Water can also form hydrogen bonds with other materials, an attraction referred to
as adhesion. Two important properties of water, surface tension and capillarity, are a result of these
attractions.
At the interface between water and air, the water molecules are arranged in an ordered
pattern; they are hydrogen-bonded to each other on three sides. Since the surface molecules are
bonded on three sides instead of four, like the molecules in the bulk of the fluid, water acts as if it is
coated with a film. It is this surface tension that causes the water to “bead up” or form a sphere, on a
hard, non-wettable surface. Surface tension allows us to skip rocks on the water and water strider to
“walk on water.”
Capillarity forces liquids into small pores. This is how water moves through dry soil. The forces
of adhesion and cohesion are both necessary to explain capillarity. For example, water clings to glass by
adhesion and this attraction pulls the water up the sides of the tube. Since water is hydrogen-bonded to
itself, the molecules moving up the tube pull other water molecules up along with them. Movement
stops when the weight of the water column is greater than the force of capillarity.
Water resists temperature change. Heat energy is required to break hydrogen bonds. When
water is heated, most of the heat is used to break hydrogen bond and not much is left over to actually
raise the temperature of the water. (Increases the kinetic energy of the water molecules). The specific
heat of any substance is that amount of heat required to raise, or lower, the temperature of 1g of the
substance 1 degree C and is measured in calories/g/C. Compared to other substances, water has a high
specific heat (table 1) an attribute important in biological systems. Organisms generate considerable
heat in carrying out metabolic activities and the high water content of cells acts as a buffer against
radical temperature fluctuation. Much heat can be absorbed by the cell water with little change in
temperature of the organism. On a larger scale, the water that covers most of the Earth resists
temperature change and creates a hospitable environment for life.
Hydrogen bonds make it difficult for water molecules to escape the liquid state and are
responsible for water’s high heat of vaporization the amount of heat required for 1 g of a substance to
be converted from a liquid to a gas. The bonds must be broken before water can evaporate and this
requires considerable energy. Our body temperature is maintained when we get hot, sweat and the
water evaporates from our skin cooling us. Water also helps moderate global climate by absorbing solar
radiation and dissipating the heat by evaporation of surface water. In addition to a high heat of
vaporization, water has a high boiling point, 100 C.
Water is also unique in the way temperature affects its density. Most substance increase in
density as temperature decreases, the density of water increases as it is cooled to 4 C and then its
density begins to decrease as temperature decreases to 0 C, the freezing point of water. As the freezing
point is approached, hydrogen bonds relax and form a lattice that is looser in character then liquid water
(the molecules are further apart). This is the reason why ice floats and ponds don’t freeze solid. The
freezing of water (releases of heat) and melting of ice (absorbing of heat) also help moderate global
climate.
Table 1. Specific Heat and Heat of Vaporization of Common Liquids
Liquid
Specific Heat
Heat of Vaporization
(cal/g/C)
(cal/g)
Acetic Acid
.47
87
Ammonia
1.23
302
Ether
.52
84
Ethyl Alcohol
0.60
237
Mercury
.03
73
Turpentine
.41
68
Water
1.09
640
Objectives:
1.
2.
3.
4.
5.
Learn how polarity of the water molecule affects its behavior.
Use the properties of cohesion and adhesion to explain surface tension and capillarity.
Compare the temperature stability of water to that of another substance.
Illustrate the high heat of vaporization of water.
Compare the density of ice to that of liquid water.
A. Bonding:
Observe the polar nature of water by attempting to “band” a stream of water with a balloon.
Materials:
Balloon
Water stream from faucet
Procedure:
1. Blow the balloon up.
2. Turn the faucet on so there is a steady stream.
3. Rub the balloon in your hair to develop a static charge.
4. Hold the balloon close to the stream and observe. Move the balloon up and down
the stream and observe. Repeat, holding the balloon on the other side of the
stream.
5. Record the results in the two trials.
B. Cohesion:
Test water: water is attraction by observing surface tension.
Materials:
Wax paper
Scissors
Dropper
Diluted detergent
Lens paper
Petri dish
Pins
Ethanol
Toothpicks
Water
Procedure:
1. Cut a 5cm X 5cm square of wax paper and one of lens paper.
2. Place a drop of water on the left side of the wax paper and a drop of ethanol on the right
side. Observe the shape of the drops and record observations.
3. Fill a petri dish with water.
4. Carefully place the piece of lens paper on the surface of the water in the dish.
5. Place a pin on the lens paper. Use 2 toothpicks to gently push the paper to the bottom of
the dish. Observe the position of the pin and the surface of the water next to it.
6. Add 5 drops of liquid detergent to the surface of the water at the edge of the dish. Observe
the position of the pin.
7. Record your observations.
C. Adhesion:
Test the attraction of water for other substances by observing its movement through pores.
Materials:
Paper towel
Scissors
Ruler
Water filled petri dish
Procedure:
1. Cut a 5cm X 5 cm square of paper towel.
2. Touch one tip of the paper towel to water in the dish. Observe water movement across the
towel.
D. Temperature Stability:
Measure the rate with which an equal mass of sand and of water, heated to 80 C, loses heat by
recording the temperature of each substance at 2 minute intervals until the water and sand
have each cooled to approximately 50 C.
Materials:
Hot plate
Balance
Erlenmeyer flasks, 50 ml
Beakers, 300 ml
Dry sand
Water
Saran wrap + thermometer
Procedure:
1. Obtain 2 Erlenmeyer flasks , one with 50 g of water, one with 50 g of dry sand. Cover with
saran wrap and insert thermometer into the flask.
2. Add 250 ml of water to a 300 ml beaker and place one flask into each beaker of water.
3. Place each beaker on a hot plate. Heat until the temperature in the flasks reach 80 C. Note:
The 2 flasks may not reach 80 C at the same time, so you may have to begin step 4 at
different times for the 2 flasks.
4. Set the flask (sand or water ) @ 80 C on the counter. Note the time.
5. Record the temperature of each flask, at two-minute intervals, for a period of 16 minutes.
E. Density
Observe the change in total volume of an ice water solution as ice melts.
Materials:
Graduated cylinder, 50 ml
Spatula
Dropper
Beaker of ice water @ 4 C
Procedure:
1. Use the spatula to pack ice into the cylinder until the ice comes just below the 50 ml
graduation.
2. Fill the dropper with ice water and use to fill the cylinder to the 50 ml mark. Agitate the
dropper to remove all air bubbles from the ice water. Be sure to read the water meniscus at
eye level. The bottom of the meniscus should be directly on the top of the 50 ml
graduation.
3. Observe the water level as the ice melts. When all of the ice has melted, record the volume
of the water in the cylinder.
F. Heat of Vaporization
Demonstrate the cooling property of water by comparing heat loss from a wet and dry bulb
thermometer.
Materials:
Thermometer
Ring stand and clamps
Cheese Cloth
String
Scissors
Water
Fan
Procedure:
1. Cut a 2” X 4” square of cheese cloth. Carefully fasten it around the bulb of one of the
thermometers mounted on the ring stand. Secure it with string.
2. Position the fan so it blows equally on each of the 2 thermometers.
3. Bring the temperature of each thermometer to 40 C by placing the bulbs in a beaker of hot
water.
4. Squeeze the gauze gently to remove excess water. Carefully dry the other thermometer.
5. Record the temperature of each thermometer.
6. Turn on the fan and record the temperature of each thermometer and one minute intervals
for 5 minutes.
Results and Conclusions:
Draw diagrams of water that you observed and describe what happened in each case using what
you know about the structure of water molecules and hydrogen bonds. Illustrate what must be
happening on a molecular level.
More specifically . . .
Bonding: Assume the balloon carried a positive charge; show how a water molecule would align itself in
relation to the balloon.
What would happen if water splashed on the balloon? Why?
Cohesion: Explain why each liquid acted as it did.
Describe, as well as draw the appearance of the water surface adjacent to the floating pin.
Explain what happened to the pin when the detergent was dropped on the water surface, and
why.
Adhesion:
Describe the movement of the water across the paper towel. Do you think the water would behave in a
similar fashion if you substituted a piece of notebook paper for the paper towel? Does your explanation
suggest how the environment might affect water movement, for example in soil?
Temperature Stability:
Construct a graph from the raw data. How does the high specific heat of water relate to its temperature
stability?
Density: Explain any difference in volume between the ice + water mixture and water alone. Would the
initial proportion of ice:water have any bearing on the final volume of water (i.e. if you added less ice
and more 4 C water, would your final volume be different)?
Heat of Vaporization: Explain any difference between the 2 thermometers.
Refer to table 1 in the introduction. If you have equal quantities of ammonia and ethyl alcohol
and were interested in using one as a coolant, which would you choose and why?
Extension Research:
Find one product that affects how water behaves, such as Rain-X. Research the product and
explain how the product works based on your knowledge of water’s properties.