What else do you know
about water?
• How does the molecule look?
• How does it function?
• What can it do in our everyday lives?
The Extraordinary
Properties of Water
Learning Objectives
• Understand the nature of the water
molecule and its unique properties
and how these are altered by the
presence of salt in solution.
Water
• In case you missed yesterday:
• A water molecule (H2O), is
made up of three atoms --one oxygen and two hydrogen.
H
H
O
Water is Polar
• In each water molecule, the oxygen
atom attracts more than its "fair
share" of electrons
• The oxygen end “acts” negative
• The hydrogen end “acts” positive
• Causes the water to be POLAR
• However, Water is neutral (equal
number of e- and p+) --- Zero Net
Charge
Hydrogen Bonds Exist
Between Water Molecules
• Formed between a highly
Electronegative atom of
a polar molecule and a
Hydrogen
• One hydrogen bond is
weak , but many
hydrogen bonds are
strong
Interaction Between Water
Molecules
Negative Oxygen end of one water molecule is
attracted to the Positive Hydrogen end of another
water molecule to form a HYDROGEN BOND
What are
the
Properties
of Water?
Water’s Physical Properties
• Water is unique in that it is the
only natural substance that is found
in all three states -- liquid, solid
(ice), and gas (steam) -- at the
temperatures normally found on
Earth.
Water’s Physical
Properties
• Water's freezing and boiling points
are the baseline with which
temperature is measured: 0o on the
Celsius scale is water's freezing
point, and 100o is water's boiling
point.
Do you think the boiling point
remains the same at higher
elevations?
Properties of Water
• Cohesion
Properties of Water
• Cohesion
• Adhesion
Properties of Water
• Cohesion
• Adhesion
• High Specific Heat
Properties of Water
• Cohesion
• Adhesion
• High Specific Heat
• High Heat of Vaporization
Properties of Water
• Cohesion
• Adhesion
• High Specific Heat
• High Heat of Vaporization
• Less Dense as a Solid
Cohesion
• Attraction between particles of the
same substance ( why water is
attracted to itself)
• Results in Surface tension (a measure
of the strength of water’s surface)
• Produces a surface film on water that
allows insects to walk on the surface
of water
Cohesion & Surface Tension
Helps insects walk across
water
Cohesion
• What will happen when water molecules come in
contact with each other?
• Grab a dropper from the middle of your table, use
proper technique to fill it with the blue-colored water.
• Lay out a sheet of wax paper. Slowly begin adding
drops of the water to the wax paper (spread out the
drops).
• What will happen when you move the drops around
with the toothpick? Try it.
• Floating paper clip made of steel with
copper plating. The high surface tension
helps the paper clip - with much higher
density - float on the water
Compare the Surface Tension of
Water to other liquids
Materials:
•
•
•
•
•
•
•
Paper towel
Tray
Penny
Water
Alcohol
Vinegar
Soap water
Compare the Surface Tension of
Water to other liquids
Before you begin, make a prediction: How
many drops of water will fit on the penny
before it overflows?
Adhesion
• Attraction between two different
substances.
• Water will make hydrogen bonds with other
surfaces such as glass, soil, plant tissues,
and blood in the body.
Water on a String
• Materials (for 1 table):
1. 2 plastic cups (1 half way filled with
water)
2. Long piece of cotton string
3. Tape
Water on a String
• Think about the properties of water
we have talked about so far. What do
you predict will happen?
Water on a String
• Instructions:
1. Dunk all but an inch of your string in
water.
2. Tape the dry part of the string
inside the empty cup.
3. Hold the other end of the string
inside the water-filled cup with your
finger.
4. Pour SLOWLY
Capillary Action
• Water molecules will “tow” each
other along. It is the movement
of water within the spaces of a
porous material due to the forces
of adhesion, cohesion, and surface
tension.
• Example: transpiration process
which plants absorb water from the
soil; it moves through the plant to
evaporate from leaves.
Adhesion Causes Capillary
Action
Which gives water the
ability to “climb”
structures
You can see capillary action in action (although slowly) by
doing an experiment where you place the bottom of a
celery stalk in a glass of water with food coloring and
watch for the movement of the color to the top leaves of
the celery.
Adhesion Also Causes
Water to …
Form spheres &
hold onto plant
leaves
Attach to a
silken spider
web
Surface Active Agents
• In cleaning, surface tension must be
reduced so water can spread and wet
surfaces.
• Chemicals that are able to do this
effectively are called surface active
agents, or surfactants. They are said
to make water "wetter."
Surfactants
• Surfactants perform other important
functions in cleaning:
– loosening, emulsifying (dispersing in
water)
– holding soil in suspension until it can be
rinsed away
• Surfactants can also provide
alkalinity, which is useful in removing
acidic soils.
Surfactants in “Action”
• Materials (for 3-4 people/1 table):
1.
2.
3.
4.
Tray with water
2 Index cards
Scissors
Cup with dish soap
Surfactants in “Action”
• Put one index card on top of the
water at one end of the tray.
• What happens?
Surfactants in “Action”
• Cut a small triangle out of one end of the
index card (less than an inch)
• Use the tip of your finger to add a SMALL
amount of soap to the inside EDGES of the
triangle/ the V notch (don’t put too much!)
• Place the index card at one end of the
tray.
• What happens? Why?
High Specific Heat
• Amount of heat needed to raise or
lower 1g of a substance 1° C.
• Water resists temperature change,
both for heating and cooling. IT’S
A HEAT SINK! The Ocean acts as
a tremendous heat sink to moderate
the earth's temperature.
• Water can absorb or release large
amounts of heat energy with little
change in actual temperature.
High Specific Heat
• Water has a high specific heat index.
This means that water can absorb a lot
of heat before it begins to get hot.
– This is why water is valuable to industries
and in your car's radiator as a coolant.
High Heat of Vaporization
• Amount of energy to convert 1g of
a substance from a liquid to a gas
• In order for water to evaporate,
hydrogen bonds must be broken.
• As water evaporates, it removes a
lot of heat.
High Heat of Vaporization
• Water's heat of vaporization is 540
cal/g.
• In order for water to evaporate,
each gram must GAIN 540 calories
(temperature doesn’t change --100oC).
• As water evaporates, it removes a
lot of heat with it (cooling effect).
• Water vapor forms a kind of
global ‘‘blanket” which helps to
keep the Earth warm.
• Heat radiated from the sunwarmed surface of the earth is
absorbed and held
by the vapor.
Morning Do
9-11-15
Objective: TLW demonstrate the basic
principles of fluid dynamics by determining
which has a greater density -- fresh or salt
water, warm or cold water.
1. What two properties of water play a
part in capillary action?
2. What must break in order for water
to evaporate?
Water is Less Dense as a
Solid
• Ice is less dense as a solid than as a
liquid (ice floats)
• Liquid water has hydrogen bonds that
are constantly being broken and
reformed.
• Frozen water forms a crystal-like
lattice whereby molecules are set at
fixed distances.
Water is Less Dense as a
Solid
•Which is ice and which is water?
Water is Less Dense as a
Solid
Water
Ice
Temperature & Salinity
affect Density of Water
• Complete lab activity in your group
• You will need to assign tasks:
– 1 Reader (you will read ALL instructions on
lab)
– 1 Recorder (you will record all of the
information on your lab sheet)
– 1-2 Doers (you will be collecting materials and
performing procedures)
Density
• Cold, salty water is more dense than
warm, fresh water and will sink below
the less dense layer.
– Density is defined as the measure of a
material's mass (e.g. grams) divided by its
volume (e.g. milliliters).
• Mixing of seawater influences the
density of seawater thereby affecting
ocean circulation.
Density of Water
• High density in cold, salty waters
–why is this important?
– Big Idea
• Two of the most important
characteristics of ocean water are its
temperature and salinity. Together
they help govern the density of
seawater, which is a major factor
controlling the ocean's vertical
movements and layered circulation.
Homeostasis
• Ability to maintain a steady state
despite changing conditions
• Water is important to this process
because:
a. Makes a good insulator
b. Resists temperature change
c. Universal solvent
d. Coolant
e. Ice protects against temperature
extremes (insulates frozen lakes)
Solutions & Suspensions
• Water is usually part of a
mixture.
• There are two types of
mixtures:
– Solutions
– Suspensions
Solution
• Ionic compounds disperse as ions in
water
• Evenly distributed
• SOLUTE
– Substance that is being dissolved
• SOLVENT
– Substance into which the solute
dissolves
Solution
Suspensions
• Substances that
don’t dissolve but
separate into tiny
pieces.
• Water keeps the
pieces suspended
so they don’t
settle out.
Turbidity
• The amount of particulate matter
that is suspended in water.
• Material that causes water to be
turbid include: clay, silt, plankton,
organic and inorganic matter, &
microscopic organisms.
• Turbidity is measured by shining a light
through the water and is reported in
nephelometric turbidity units (NTU).
Acids, Bases and pH
One water molecule in 550 million
naturally dissociates into a Hydrogen
Ion (H+) and a Hydroxide Ion (OH-)
H2O 
H+
Hydrogen Ion
Acid
+ OH
-
Hydroxide Ion
Base
The pH Scale
• Indicates the concentration of H+
ions
• Ranges from 0 – 14
• pH of 7 is neutral
• pH 0 up to 7 is acid … H+
• pH above 7 – 14 is basic… OH• Each pH unit represents a factor of
10X change in concentration
• pH 3 is 10 x 10 x 10 (1000)
stronger than a pH of 6
Acids
• Strong
Acids
have a pH
of 1-3
• Produce
lots of
H+ ions
Bases
• Strong
Bases have
a pH of 11
to 14
• Contain
lots of OHions and
fewer H+
ions
The pH Scale
Buffers
• Weak acids or bases that react with
strong acids or bases to prevent
sharp, sudden changes in pH
(neutralization).
• Produced naturally by the body to
maintain homeostasis
Weak Acid
Weak Base