Observing the Properties of Water Lab
Biology H
Purpose: To observe and describe the properties of water.
Background:
Water is a simple, small molecule, and without it, life on Earth could not exist! The molecule is
made up of two hydrogen atoms and one oxygen atom. The bonds between the atoms are called
covalent bonds, because the atoms share electrons, but the electrons are shared unequally. The oxygen
atom pulls more strongly on the electrons than the hydrogen atoms do. This causes a partial negative
charge on the oxygen end of the molecule and a slightly positive charge on the hydrogen ends. A water
molecule, because of its shape, is a polar molecule. That is, it has one side that is positively charged and
one side that is negatively charged.
The polarity of a water molecule also enables it to form bonds with many other kinds of
molecules. The positive hydrogen side of the molecule is attracted to negatively charged molecules or
negative parts of other molecules. The negative oxygen side of the molecule is attracted to positively
charged molecules or positive parts of other molecules.
When two water molecules get close together, the polar forces work to draw the molecules
together. The oxygen atom of one water molecule will bond with hydrogen atoms of other water
molecules. These bonds are called hydrogen bonds. A single water molecule may form as many as four
hydrogen bonds at the same time. This ability to form multiple hydrogen bonds is responsible for many
of water’s properties.
Hydrogen bonds are not as strong as covalent bonds, but they are strong enough to bind water
molecules together and give water its unique characteristics. (An analogy concerning the bonds is that
the covalent bonds are like a strong glue bond while the hydrogen bonds are like the bond between two
magnets.) Weak hydrogen bonds between the molecules of water must be separated in order for water
to change form. Separating these hydrogen bonds requires energy. These bonds, which are constantly
forming, breaking, and reforming, only last for a fraction of a second. At any time, a large portion of the
molecules present are bonded to other water molecules. Because of this, changing the temperature of
water requires adding or removing more heat than any other naturally occurring material on Earth
requires.
This polarity and ability to form hydrogen bonds gives water many unique properties.
Water exhibits cohesion, adhesion, has a high surface tension, is a universal solvent, is less dense as a
solid that as a liquid, has a high heat of vaporization and allows capillary action to occur.
Cohesion: an attraction between molecules of the same substance. Because of hydrogen
bonding, water is extremely cohesive. Water’s cohesion causes molecules on the surface of water to be
drawn inward, which is why drops of water form beads on a smooth surface.
Adhesion: an attraction between molecules of different substances. When you read the volume
of water in a graduated cylinder the surface of the water dips slightly in the center and rises on the
sides. This is because the adhesive forces between the glass and the water are stronger than the
cohesive forces that hold the water molecules together.
High Surface Tension: describes the “stickiness” of water molecules on the surface of water. The
cohesion of water molecules creates a strong film on the water’s surface. Surface tension allows water
to hold up materials heavier and denser than itself. This explains why some insects and spiders can walk
on a pond’s surface.
Universal Solvent: water’s polarity gives it the ability to dissolve both ionic compounds and
other polar molecules. Living things are, in part, composed of mixtures involving water. Water is the
solvent; the dissolved substances are the solutes.
Density: water is one of the few substances that is less dense as a solid that as a liquid, so ice
floats on liquid water. While other materials contract and become more dense when they solidify, water
expands into an evenly distributed crystalline structure. This is due to the hydrogen bonds inside water
molecules. These bonds keep the water molecule far enough apart to make ices just dense enough to
float on the liquid surface.
High Heat of Vaporization: it takes a lot of energy to break liquid molecules away from each
other because the hydrogen bonds are able to reform very quickly. In order for water to become a gas
(steam) enough energy has to be put in to break all the hydrogen bonds holding a liquid water molecule
to the other liquid water molecules. This allows water to absorb a great deal of heat without changing
temperature very much.
Capillary action: the tendency of water to rise in a thin tube against the force of gravity. Water
molecules are attracted to each other by cohesive forces and are attracted to other substances due to
adhesion. Due to the polarity of water molecules and their ability to form hydrogen bonds, they are able
to stick to each other and to other polar molecules. Water is attracted to the walls of a thin tube, stick to
them due to adhesion, and can exert a force on other water molecules behind them due to cohesion.
This force allows water molecules to enter thin tubes, for example plant root hairs, and move up a plant
in the xylem vessels.
Lab Procedure:
Each pair of students at the lab table will complete part of this lab. You will then share the results with
the other students at the table so everyone will have all the data and be able to answer the questions
for all of the experiments.
Station 1: Drop by Drop
Materials: a penny, beakers/dropper bottles of: water, soapy water, alcohol, oil, paper towels,
pipettes
1. Predict how many drops of each solution you will be able to put onto the penny without any
spillover. Record your predictions on your data table.
2. Place a clean penny on a paper towel. Using the dropper bottle or one the solutions in the
beakers, add drops of the solution being tested, one at a time, to the surface of the penny.
DO NOT LET THE DROPPER TIP OR PIPETTE TOUCH THE SOLUTION ALREADY ON THE PENNY.
3. Record the maximum number of drops on your data table. Draw how the penny looks from
the side right before the solution spills off the edge.
4. Dry the penny and repeat 2 more times. Record the values on your data table and calculate
the average value for each solution.
5. Conduct 3 trials for each solution. Record the maximum number of drops on your data
table, draw the penny from the side and calculate the average for each solution.
Station 2: Paper Clips: Float or Sink
Materials: plastic cup, petri dish, paper clips, water, dropper bottle of soap
Part A
1. Place a clean cup on a paper towel. Fill it to the brim with water.
2. Carefully add 1 paper clip at a time so it sinks to the bottom of the cup until the water spills
over.
3. Record the number of paper clips you were able to add without spilling over on your data
table.
4. Pour the water into your waste cup. Remove and dry the paper clips and return them to
your lab tray.
Part B
1. Fill the petri dish ½ full with water.
2. Carefully float a paper clip on top of the water.
3. Add 1 drop of soap to the water. Describe what happens.
4. Empty the petri dish into your waste container. Wash the dish and paper clip well, dry them
and return them to your lab tray. Empty the waste cup in the sink and refill the water bottle
from the sink for the next group to use.
Station 3: Rise Up/All mixed up
Materials: petri dish, 50 mL beaker, 3 capillary tubes (small, medium and large diameter), food
coloring, 3 small test tubes, beakers of water, alcohol, and oil, pipettes
Part A: Rise Up
1. Put 30 mL of water into your beaker. Add 1-2 drops of food coloring and swirl to mix. Pour
into your petri dish.
2. Place the largest diameter capillary tube into the water WITHOUT it touching the bottom.
Let stand for 15 seconds. Measure (in mm) the distance the water rises into the tube.
Record the diameter of the tube and the distance the water rose on your data table.
3. Repeat with the medium and small diameter capillary tubes. Record the diameter of each
tube and the distance the water rose on your data table.
4. Rinse your petri dish and beaker in the sink and dry them. Wick the water out of the
capillary tubes using paper towels. Return all the clean materials to your lab tray.
Part B: All Mixed Up
1. Add 2mL of each solution in the order given into 3 small test tubes.
a. Tube 1: oil and water
b. Tube 2: alcohol and water
c. Tube 3: Alcohol and oil
2. Put your finger over the opening in the tube and invert gently 2-3 times to mix. Record your
observations. Make a labeled sketch of each tube.
3. Empty the tubes into the sink with lots of running water. Add a drop of soap and thoroughly
wash and rinse each tube. Place them upside down into the rack in your lab tray to dry.
Station 4: See the Rainbow/Cool me off
Materials: Chromatography paper, black overhead marker, test tube, water, alcohol, cotton
swabs, ruler
Part A: See the Rainbow
1. Cut a “V” shape at the bottom of the strip of chromatography paper about 1 cm from the
bottom of the paper. Draw a pencil line across the paper where the “V” ends.
2. Place 1 dot of black overhead marker on the pencil line.
3. Place the bottom of the paper, “V: side down into the test tube. The tip of the paper should
be in the water but the dot of ink should be above the water. Fold the top of the paper over
the top of the test tube to hold it in place.
4. Let sit several minutes until the water has moved 3/4 of the way up the paper.
5. Remove the paper from the test tube.
6. Immediately draw a pencil line where the solvent stopped moving.
7. Measure (in mm) from the pencil line to the peak of each individual color on the paper.
8. Draw the pattern you produced and record the measurements foe each color.
9. Calculate the Rf (run factor) for each color by dividing how far the color moved by how far
the water moved. Record on your data table.
Part 2: Cool Me Off
1. You will find cotton swabs soaking in a beaker of water and in a beaker of alcohol.
2. Place the ruler on your lab table and draw a chalk line 4 cm long directly onto the table.
Label one side of the line “water” and the other side “alcohol”. Remove the swabs from the
beakers, and at the same time draw a thin 4cm long line on your lab table on each side of
the chalk line. Using your phone as a timer, record how long each line takes to completely
evaporate. Be sure to put the swabs back into the right container after use.
3. Repeat and determine the average vaporization time for each solution.