The Extraordinary
Properties of Water
15.1
Objectives
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Understand the polar nature of water
•
Be able to draw a hydrogen bond
between two water molecules
•
Understand water’s special physical
properties and why they are present
Why Studying Water is
Important
•
•
•
•
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75% of Earth is covered by water
Humans are made mostly of water (62%)
Almost all chemical rxns involved in life
processes take place in water
Humans need water to survive
Water teaches a lot of important
scientific concepts
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
Hydrogen Bonding in Water
What are
the
Properties
of Water?
Properties of Water:
Boiling Point
• At sea level, pure water boils at
100 °C and freezes at 0 °C.
• The boiling temperature of water
decreases at higher elevations
(lower atmospheric pressure).
• For this reason, an egg will take
longer to boil at higher altitudes
Properties of Water
• Cohesion
• Adhesion
• High Specific Heat
• High Heat of Vaporization
and Fusion (Melting)
• Weird Density Profile
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
Adhesion
• Attraction between two different substances.
• Capillary action-water molecules will “tow”
each other along when in a thin glass tube.
• Example: transpiration process which plants
and trees remove water from the soil, and
paper towels soak up water.
Adhesion Causes Capillary
Action
Which gives water
the ability to
“climb” structures
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.
• Water = 4.18 J/goC
Chloroform = 0.54 J/goC
Copper = 0.38 J/goC
High Heat of Vaporization
• Amount of energy to convert 1g of a
substance from a liquid to a gas.
(Water’s heat of vaporization is 540 cal/g)
• In order for water to evaporate,
hydrogen bonds must be broken.
• This means water has a very low vapor
pressure. It will take longer to
evaporate than most other liquids.
High Heat of Fusion
• Water's heat of fusion is 80 cal/g
• In order for ice to melt, each gram
must GAIN 80 calories
• Compare to chloroform 17.7 cal/g
Which is ice and which is water?
Water is Less Dense as a Solid
Water (Liquid)
Ice (Solid)
Real World Examples:
Ice Less Dense Than Water
Soda cans explode in freezers
Pipes burst in cold climates
Potholes are worse in cold climates
Breakdown of rocks seen in
mountain streams (Erosion)
• Maintains life in lakes (lakes don’t
freeze from bottom up)
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•
•
•
Properties of Water
• Cohesion
• Adhesion
• High Specific Heat
• High Heat of Vaporization
and Fusion (Melting)
• Weird Density Profile
Some Cool Water Videos
Molecular Modeling of Ice Water Freezing
Ice melting
Modeling of Melting Ice
Brownian Motion of Water
Molecular Dynamics Simulator of Water