Transcript The Extraordinary Properties of Water

The Extraordinary
Properties of Water
Water
• A water molecule (H2O), is
made up of three atoms: one
oxygen and two hydrogen.
H
H
O
The Water Molecule
• Polarity
– A water molecule is polar because
there is an uneven distribution of
electrons between the oxygen and
hydrogen atoms.
(-)
(+)
•Polar water molecules
act like magnets
and attract each other
Hydrogen Bonds
-form between the negative end of
one water molecule and the positive
end of another.
-one hydrogen bond is weak , but
many hydrogen bonds are strong
Properties of Water
• What are they?
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
1. Cohesion
•Attraction between particles of the
same substance
- Explains why water is attracted
to itself
Results in:
Surface tension (a
measure of the
strength of water’s
surface)
allows insects to
walk on the
surface of water
2. Adhesion
•Attraction between two different
substances.
- water will make hydrogen bonds
with other surfaces such as glass, soil,
plant tissues, and cotton.
.
• Explains capillary actionwater molecules will pull
each other along when in a
thin glass tube.
• i.e. moves water up the
tubes of plants from roots
to leaves
3. High Specific Heat
•Water can absorb or release large
amounts of heat energy with little
change in actual temperature.
Water warms slowly, but cools slowly.
Oceans store heat.
The body (mostly water) does not lose heat
easily.
4. High Heat of
Vaporization
• In order for water to evaporate,
hydrogen bonds must be broken.
As water evaporates, it removes a
lot of heat with it.
The “extra” energy needed to break
hydrogen bonds means that
evaporating water cools surfaces.
That is why sweating is a great way to
stay cool.
5. Water is Less Dense as
a Solid
•Ice is less dense than liquid water
(ice floats).
Water is Less Dense as a
Solid
Water
Ice
Explains why
fish can live
in a lake in
the winter;
the lake
freezes from
the top down.
Solutions & Suspensions
• Water is usually part of a
mixture.
• There are two types of
mixtures:
– Solutions
– Suspensions
Solution
• Particles disperse in water
• Evenly distributed
SOLUTE
– Substance that is being dissolved
SOLVENT
– Substance into which the solute
dissolves
Solution
Acids, Bases & pH
A water molecule naturally dissociates
into a Hydrogen Ion and a Hydroxide
Ion
(Ion = charged particle)
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 – 6.99 is
• pH 7.01 – 14 is basic
• Each pH unit represents a factor of
10 change in concentration
Acids
• Strong
Acid = pH
1-3
H+ ions
Bases
• Strong
Base = pH
11 – 14
OH-ions
Buffers
• Weak acids or bases that react
with strong acids or bases to
prevent sharp, sudden changes
in pH.