Today’s Lesson: Properties of Water
Water is a Polar Molecule
Water molecules are polar.
Polar = has a positive side
and a negative side.
The negative part of a
water molecule is
attracted to the positive
part of another.
Water Forms Hydrogen Bonds
The attraction between
water molecules are called
Hydrogen bonds between
molecules of water is what
causes water’s surface tension
Water’s Boiling and Freezing Points
Water is considered to be so important that the scale we
use to measure temperature was set according to water!
At sea level (about 1 atmosphere of pressure):
Water boils at 100° Celsius
Water freezes at 0° Celsius
Frozen water (ice) is less dense than liquid water, which
is why ice floats.
Water is most dense (heaviest) at 4° Celsius.
Can Water’s Boiling Point Change?
Water’s boiling AND freezing points depend on how much
pressure is on the water.
When there is less pressure from the atmosphere, water will have
a lower boiling point!
When there is more pressure from the atmosphere, water will
have a higher boiling point!
What if there is no pressure on water, like in a vacuum or in outer
As the pressure is lowered, the boiling point gets lowered.
As you go
The Science of Cooking with Water
Can we make water boil hotter than 100° Celsius?
YES! Pressure increases the boiling point.
So, why do you think people use a pressure cooker?
It is so they can cook things in water that is hotter
than 100° Celsius.
Boiling Water and Space
How much pressure is there in space?
Space has very little, to no pressure.
So what is a space suit really for?
A human body is about 70% water. With no pressure, all the
water in a human would boil! NASA says that a person could
live about 1 minute in space without a suit.
Note: (don’t need to write in notes) a man accidentally exposed
to a vacuum at NASA lost consciousness after about 14 seconds
due to lack of oxygen. He said his last memory was “the water
beginning to boil on his tongue”. You will NOT explode without
a spacesuit in space says NASA.
More about Boiling Water
How do you know when water is at 100° Celsius
When the first bubble of air floats all the way to
the top of the water.
Do you need to make water boil like crazy for it
to be 100° Celsius?
No! Just enough for the first bubbles to be rise
to the top. After that, it only needs a little heat
to stay at 100° Celsius.
What are the bubbles in boiling water made of?
Steam (=water vapor)
Capillary action occurs when water goes up
a narrow tube against the forces of gravity.
Without hydrogen bonds, capillary action
could not occur.
Capillary action is how plants and trees
transport water from the roots to leaves
where photosynthesis occurs.
How Does Capillary Action Occur?
1) Adhesion is the attraction between water
and other objects.
Example of Water Adhesion
Adhesion allows water to stick to the sides
of the tube (can be a straw or inside a
2) Cohesion is water being attracted to itself
due to its hydrogen bonds
Adhesion and cohesion lead to water’s capillary action
Water has a Very High Specific Heat Capacity
Specific heat is how much energy is required to heat a substance.
Water needs a LOT of energy to be heated, so WATER HAS A VERY
HIGH SPECIFIC HEAT CAPACITY.
To heat things you need to make the molecules move faster.
It is hard to make water
molecules move fast
because its hydrogen bonds
keep the molecules stuck
Cold (dense) or Hot (less dense)??
Density is mass/volume!
Cold and dense
Hot, less dense
Water Has Surface Tension
What is surface tension?
Surface tension is the ability of a liquid to “push back” on
Surface tension allows water striders to walk on water.
Surface tension allows this
paper clip to “float” on
What Causes Water’s Surface Tension?
How does water hold the paper clip up?
COHESION causes surface tension.
But, surface tension is due to the molecules
at the surface having stronger hydrogen bonds
Water molecules are
surrounded only on one
side at the surface, and the
H-Bonds are therefore
Is Water an Acid???
Pure water is not an acid (not acidic).
BUT, when water is exposed to air, it comes in contact with carbon
dioxide (CO2) and forms a weak acid called carbonic acid:
CO2 + H2O
Carbonic acid can dissolve rock and things like cement.
Is Water an Acid???
Over time, water is responsible for carving out large cave systems
like Carslbad Caverns. So, YES, water can be an acid.
the power to
Tell me 3 things water could NOT do if it was not a polar molecule.
Draw a diagram of a hydrogen bond. Label the oxygen and
hydrogen atoms and the hydrogen bond.
Which is heavier: 5 liters of water at 4° Celsius, or 5 liters of water
at 50° Celsius or 5 liters of ice at 0° Celsius?
Where will water boil hotter, Bangkok or Chiang Mai?
True or False: A pressure cooker can cook faster because the water
inside is able to get hotter than 100° Celsius.
Tell me how you know when water is 100° Celsius when cooking.
What would happen to a human in space without a spacesuit?
Draw a diagram of capillary action in a plant.
What is adhesion?
What is cohesion?
Tell me one reason why water’s high specific heat may be
important for a human body.
You are walking on the street and see some holes in the sidewalk.
Explain to me how water may have caused these holes.
What does “hydro” mean? What does “phobic” mean? Is water a
Why does water have such a high specific heat capacity?