Chem Props of Water

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1

Forms of Water

2



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

4

4

Water’s Properties










Cohesion
Adhesion
Capillarity
High Specific Heat
High Heat of Vaporization
Solid water (ice) is less dense than liquid
Solvent
Transparency
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Cohesion


Cohesion refers to
attraction to other
water molecules.
 responsible for
surface tension

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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 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!

You
don’t
say!

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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







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
14
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...
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