Name: ______________________________________________________Period: ______Alpha#: ______
Lab activity: Exploring the Properties of Water
Objective: Explore the properties of water through hands on activities
Introduction: You probably know water's chemical description is H2O. As the diagram to the left shows, that
is one atom of oxygen covalently bonded to two atoms of hydrogen. The hydrogen atoms are
considerably smaller that the oxygen atoms,
resulting in the water molecule having the
shared electrons of its covalent bond spend
more time around the oxygen atom than the
two hydrogen atoms. This causes a positive
charge on the side where the hydrogen atoms
are and a negative charge on the other side,
where the oxygen atom is. As the right-side
diagram shows, the side with the hydrogen
atoms (positive charge) attracts the oxygen
side (negative charge) of a different water
molecule. This attraction creates a hydrogen
bond.
These hydrogen bonds make water molecules ‘stick’ to each other a property known as
cohesion. Water also has a very high surface tension caused by this property. Surface
tension is a measure of the strength of the water's surface film. The cohesion between the
water molecules creates a strong film which permits water to hold up substances heavier
and denser than it. The hydrogen bonds make water sticky and elastic, so it tends to clump
together in drops rather than spread out in a thin film.
Water molecules can also ‘stick’ to other materials, particularly solids, a property known as
adhesion. Water can climb, seep into, and seep under materials due to capillary action a
combination of these two properties. When the adhesion to a surface is stronger than the
cohesion between water molecules, water will be ‘pulled’ along as each molecule ‘sticks’ to
the surface and then also ‘sticks’ to the one behind it pulling it along like the illustration on
the right.
Water is called the "universal solvent" because it dissolves more substances than any other
liquid. Water’s dissolving ability is related to its molecular structure. Both ionic and polar
covalent compounds dissolve in water but molecules that are non-polar and have no charge
cannot dissolve in water. Remember: Like dissolves like.
Procedure: Follow the directions in each section and record your observations on this
sheet. Be sure to use your knowledge of water’s properties (hydrogen bonding!) and diffusion to answer the
questions.
Station 1
1. Drop one small drop of water onto the wax paper or acetate. Look at it from the top and from the
side.
a. Does it spread out flat or bunch up? __________________
b. Is it taller or wider? ____________________
2. Place one drop of water on a penny.
a. How many drops of water do you think you could place on a penny? _______________
b. Add water drop by drop to the surface of a penny until it spills over.
i. How many drops did it take? _____________
ii. Were you surprised at the result? Why or Why not?
iii. What kind of bond is holding the water together in a drop?
_____________________________
iv. What property of water is this? ________________________________
3. Drop one small drop of water onto the waxed paper. Carefully and gently poke the toothpick into the
drop and slowly pull it back. You should be able to see the water clinging to the toothpick and
stretching the surface of the drop. (This may take a few tries) You can even pull it around this way!
a. What property of water causes the water molecules to ‘stick’ to the toothpick?
_______________________________
b. What property of water causes them to hold together as the toothpick pulls them along?
_______________________________
2. Use your fingers to flick several small different sized drops of water onto the waxed paper or acetate.
Carefully lift up the flat surface until it is vertical.
a. Do all the drops stay on the acetate or waxed paper?_____________
b. Does the size of the drop make a difference? How?
c. If adhesion is causing the water drops to stay on the vertical surface and cohesion is holding
them together then what causes the larger drops to slide off? Hint: What force is pulling on
the drops besides the hydrogen bonds between molecules?
Station 2
1. Fill the Petri dish with water from the beaker using the pipette until it is even with the sides.
Holding the toothpick or paperclip as flat as possible with the plastic fork, carefully and gently
place it onto the surface of the water. DO not let the toothpick or paperclip dip below the surface
of the water! Observe and describe the surface of the water around the tooth pick or paperclip.
2. Fill the Petri dish with water from the beaker using the pipette as full as you can without it
overflowing. Be careful and go slowly. Look at the petri dish from the side.
a. Using the ruler determine many mm the water is
above the sides of the petri dish.
_______________
b. Convert your mm measurement to cm
_______________
3. Place a larger drop of water on the waxed paper or acetate. Touch the drop with the edge of a
small pierce of a paper towel. Hold the paper towel as vertical as possible. Wait at least one
minute.
a. Observe and describe what happens:
b. Use the ruler to measure how far in cm the water has climbed up the paper towel.
___________________ Now convert the cm to km: ___________________
c. What do you think would happen if we kept the towel in position longer?
d. What is the name for this property? __________________________________
4. As the molecules flow up the paper towel they are held together by hydrogen bonds.
a. Hydrogen bonds hold: molecules together or atoms together (circle one)
b. Draw a few water molecules held together by hydrogen bonds.
TURN OVER
5. Draw the atomic structure of one molecule of water below. (Oxygen: atomic number 8, atomic weight
16, Hydrogen: atomic number:1, atomic weight 1)
a. In water molecules (H2O) the H has a: +
or
– charge (circle one) while the
O has a: + or – charge (circle one).
b. Write the chemical formula for one molecule of water: _______
Station 3
1. Partially fill the paper cup with water. Add a small pinch of salt. Stir with the toothpick.
a. Which is the solvent? _________________ The solute? ___________________
b. Describe what happens after stirring the solution.
c. Sodium chloride (salt) is held together with an ionic bond in which the sodium has a positive
charge and the chlorine has a negative charge. If the rule is that ‘like dissolves like’ then what is
similar about the structure of water and salt?
2.
Partially fill the paper cup with water. Add a few drops of oil and stir with a toothpick.
a.
Which is the solvent? _________________ the solute? ___________________
b.
Describe what happens after stirring the solution.
c. Oils are held together with covalent bonds that share the electrons equally all along the molecule.
If ‘like dissolves like’ why does oil not dissolve in water?
Station 4
1. Fill a beaker with 50ml of water. Add one drop of food coloring.
a. What happens to the food coloring after 1 minute?
b. What do you think will happen if you left it there for 5- 10 minutes?
c. When you dropped in the food coloring you created an area of high concentration in the water
compared to the rest of the water which had a low (or no) concentration of food coloring. This
movement of the food coloring molecules from an area of high concentration into the areas
of low concentration over time is called:
________________________
2. Take 2 small beakers. Fill one with cold water and one with hot water. Use the same amount of
water in each. Drop one drop of food coloring into each.
a. Observe and compare the beakers for one minute. Describe what you see.
b. Why was there a difference in the diffusion rate between the two beakers? Hint: The warmer a
substance is the more energy the molecules have (Brownian motion)
3. Take 2 small beakers. Fill each with the same amount of the same temperature water. Add 5 drops
of food coloring to one beaker and one drop to the other.
a. Observe and compare the beakers for one minute. Describe what you see.
b. The greater the difference between the areas of high and low concentration the faster the initial
rate of diffusion. Does this agree with your results?