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< 0o C - ice;
0o C - 100o C – liquid; > 100o C - steam
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•
Water consists of an Water is a Polar Molecule
oxygen atom bound to
-has oppositely charged
two hydrogen atoms
ends
by two single covalent
bonds.
– Oxygen has
unpaired & paired
electrons which
gives it a slightly
negative charge
while Hydrogen has
no unpaired
electrons and shares
all others with
Oxygen
– Leaves molecule
with positively and
negative charged
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ends
Water molecules form Hydrogen
bonds
slightly positive
charge
hydrogen bond
between (+) and (-)
areas of different
water molecules
slightly negative
charge
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Water’s Properties
•
•
•
•
•
•
•
•
Cohesion
Adhesion
Capillarity
High Specific Heat
High Heat of Vaporization
Solid water (ice) is less dense than liquid
Solvent
Transparent
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Cohesion
•
Water clings to polar
molecules through
hydrogen bonding
– Cohesion refers to
attraction to other
water molecules.
 responsible for
surface tension

a measure of the
force necessary to
stretch or break
the surface of a
liquid
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Adhesion
–
Adhesion refers
to attraction to
other
substances.
 Water is
adhesive to
any substance
with which it
can form
hydrogen
bonds.
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Capillary action
water evaporates from
leaves = transpiration
adhesion,
cohesion and
capillary action
water taken up by
roots
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•trees have specialized structures to transport water:
xylem and phloem “plumbing”
• water molecules are “dragged” from the roots to the
top of the tree by capillary action and cohesion:
hydrogen bonds help water molecules stick to each
other
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High Specific Heat
–
High specific heat
 Amount of heat that must be
absorbed or expended to change
the temperature of 1g of a
substance 1o C.
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Impact of water’s high specific heat ranges from
the level of the whole environment of Earth to that
of individual organisms.
•
•
•
•
A large body of water can absorb a
large amount of heat from the sun in
daytime and during the summer, while
warming only a few degrees.
At night and during the winter, the
warm water will warm cooler air.
Therefore, ocean temperatures and
coastal land areas have more stable
temperatures than inland areas.
The water that dominates the
composition of biological organisms
moderates changes in temperature
better than if composed of a liquid
with a lower specific heat.
The Earth is over
75% water!
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High Heat of Vaporization
–
High heat of vaporization
 Amount of energy required to change
1g of liquid water into a gas (586
calories).
 large number of hydrogen bonds
broken when heat energy is
applied
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•
•
•
As a liquid evaporates, the
surface of the liquid that remains
behind cools - Evaporative
cooling.
Evaporative cooling moderates
temperature in lakes and ponds
and prevents terrestrial
organisms from overheating.
Evaporation of water from the
leaves of plants or the skin of
animals removes excess heat.
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“Universal” Solvent
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•
•
•
A liquid that is a completely homogeneous
mixture of two or more substances is called a
solution.
– A sugar cube in a glass of water will eventually
dissolve to form a uniform mixture of sugar
and water.
The dissolving agent is the solvent and the
substance that is dissolved is the solute.
– In our example, water is the solvent and sugar
the solute.
In an aqueous solution, water is the solvent.
Water is not really a universal solvent, but it is
very versatile because of the polarity of water
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molecules.
•
Water is an effective
solvent as it can form
hydrogen bonds.
– Water clings to
polar molecules
causing them to be
soluble in water.
 Hydrophilic attracted to
water
– Water tends to
exclude nonpolar
molecules.
 Hydrophobic repelled by water
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•
Water transports molecules dissolved in it
– Blood, a water-based solution, transports
molecules of nutrients and wastes
organisms
– Nutrients dissolved in water get
transported through plants
– Unicellular organisms that live in water
absorb needed dissolved substances
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Solid water (ice) is less dense than liquid
•
Ice is less dense than water: the molecules are
spread out to their maximum distance
Density = mass/volume
same mass
but a larger
volume
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Oceans and lakes don’t freeze solid
because ice floats
 water expands as it
solidifies
 water reaches
maximum density at
4-degrees C
 water freezes from
the top down
 organisms can still
live in the water
underneath the ice
during winter
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Water is Transparent
•
The fact that water is clear allows light to
pass through it
– Aquatic plants can receive sunlight
– Light can pass through the eyeball to
receptor cells in the back
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pH
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•
•
Water ionizes into H+ and OHH 2O
H+ and OHpH scale expresses hydrogen ion (H+)
concentration in a solution.
– logarithmic scale ranging from 0-14
 neutral = 7
 Below 7 = acid
 Above 7 = base
o
 Water at 25 C contains 1/10,000,000
mole of H+ ions = 10 -7 moles/liter

pH = -log [H+]
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pH
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Acids
•
Acids dissociate in water to increase the
concentration of H+.
– Have many H+ ions
– Sour taste
– HCl is hydrochloric acid or stomach
acid
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Bases
•
Bases combine with H+ ions when
dissolved in water, thus decreasing H+
concentration.
– Have many OH- (hydroxide) ions
– Bitter taste
– NaOH = sodium hydroxide or baking
soda
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Buffers
•
Buffers
– act as a reservoir for hydrogen ions,
donating or removing them from
solution as necessary
– Offer protection from extreme pH levels
– Produced naturally by organisms:
 Organisms can’t tolerate much pH
change
 Cells function best within a narrow
pH range
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