Notes: Water Chemistry
Water
• Water is the most important COMPOUND in
living organisms!
– Most organisms are made up of 70-95% of water
• Water serves as a form of
TRANSPORTATION
– Helps move nutrients and other substances in
and out of cells
• Water is a POLAR molecule
What is a Polar Molecule?
• POLAR: A molecule with a POSITIVE end and a
NEGATIVE end
• Water molecules are attracted to each other by
hydrogen bonds
– Remember: van der
Waals forces
Water Structure
Notice
that
opposite
charges
attract!
Water Bonding
• COHESION – an attraction
between the SAME kind of
substances
– In water: a result of hydrogen
bonds
– Attraction between water
molecules causes SURFACE
TENSION
Water Bonding
• ADHESION – an
attraction between
DIFFERENT
substances
Capillary tubes
Water & Glass
Properties of Water
1. High surface TENSION
2. Creeps up in thin tubes - CAPILLARY
action
3. High heat of VAPORIZATION
4. Resists TEMPERATURE change
5. Water EXPANDS when it freezes
6. Universal SOLVENT
1. High Surface Tension
• Water is STICKY
– Due to cohesion—
sticks to itself
• When hydrogen
bonds are broken
they quickly reform
Water striders using water
surface tension when mating.
Surface Tension
Causes the drop into a sphere
2. Capillary Action
• MOVEMENT of water within the
spaces of a porous material due
to adhesion
• Occurs because water is
“STICKY” to another substance
• Limited by gravity and the
diameter of the capillary (tube)
– Smaller the diameter, the greater
the effect
Capillary Action
Capillary action causes
the water to "climb" up
this paper towel.
Water Movement in Plants
• Water moves upward
through a plant from roots
to leave through a
COMBINATION of:
– Cohesion
– Capillary Action (adhesion)
3. High Heat of Vaporization
• Water needs a LOT
of heat to make
liquid water change
to a gas state (540
calories)
4. Resists Temperature Change
• Water can ABSORB a
tremendous amount of heat
– Moderates our climate
– It also takes a long time to cool
down
• In organisms, the ability to
control temperature enables cells
to maintain a constant internal
temperature--Homeostatsis
Water Stores Heat
• Water heats more
slowly and RETAINS
heat LONGER than many
substances
• Many organisms release
excess heat through
evaporation
– Sweating carries heat
away from the body
(HOMEOSTASIS)
5. Water Expands when it
Freezes
• Water EXPANDS
when it freezes
• Ice is LESS dense
than liquid water
• Ice FLOATS in
liquid water
6. Universal Solvent
• Many substances DISSOLVE in
water
– Commonly called the universal
solvent. Why?
• ....remember POLARITY of water
– Because of this, water in
nature and in use is rarely
pure
• Many substances are
INSOLUBLE in water. Why?
• They are NOT POLAR and not
attracted to water