Water
The Universal Solvent
• A water molecule is so small that
there are billions of molecules in a
single drop of water. About 60 million
water molecules could be stretched
side by side across a penny.
• Water is the ONLY compound that
commonly exists in all 3 phases
(solid, liquid, gas) naturally on Earth.
There would be no life on
Earth without water.
• About 2/3 of the mass of a cell is
made up of water, and most of the
biochemical processes of life occur
in aqueous solutions.
SOLVENT- the substance that does the
dissolving. (liquid)
SOLUTE- the substance that is dissolved.
(solid)
A large number of substances will
dissolve in water.
Water is the universal solvent.
•Therefore, the water inside and
outside of cells is able to carry
nutrients into and around cells and
wastes away from cells.
Water is a POLAR molecule
Polarity - the attraction of
positive and negative electrical
charges
OPPOSITES ATTRACT
Water Molecule
The Hydrogen side
is slightly positive
while the Oxygen
side is slightly
negative.
• One side of a water molecule is
slightly negative (-) and the other side
is slightly positive (+).
H
H
Positive
hydrogen
atom
O
Negative
oxygen
atom
• Individual water molecules attract
each other like magnets.
-
+
• In this way, water molecules
“stick together”.
Cohesion: the
tendency of
two SIMILAR
substances
to stick
together.
Adhesion: the
tendency of two
DIFFERENT
substances to
stick together, like
water molecules
stick to glass.
Capillary Action: the tendency of a liquid
substance to move along the surface of a
solid substance due to adhesion (as in
water climbing a glass tube or inside a
tree), even in spite of gravitational or other
forces acting in the opposite direction
Transpirati
on
• Hydrolysis- a chemical reaction where
water is involved.
• Hydrophilic- “water loving” can be
dissolved in water, polar substances.
• Ex: Salt
• Hydrophobic- “water hating” cannot be
dissolved in water, non-polar substances.
• Ex. fat, oil, soap
Like Dissolves Like
Resistance to Temperature
Change
• High Specific Heat: water is able to
absorb a large amount of heat energy
before it changes temperature.
– Specific heat: The amount of energy or
heat needed to change 1 gram water
1°C
• Water is a liquid from 0 ºC to 100 ºC
• Evaporative Cooling: water absorbs
heat when it evaporates, allowing
organisms to release excess heat.
• Heat of Vaporization: It takes a lot
more heat for water to vaporize than
just to raise its temperature a degree.
– A function of changing states of matter
– True of boiling and evaporation
• Large bodies of water can affect the
climate.
- As a result, lakes and oceans
stabilize air and land temperatures.
High Surface Tension
• Certain insects can walk on water because
of its high surface tension.
•Polarity gives water its high surface tension
through cohesion.
•Ex. Water strider
Solid expansion
For most substances, solids are more
dense than liquids. But the special
properties of water make it less dense
as a solid - ice floats on water!
When water freezes, the water
molecules line up, and as they do, they
move farther apart !
• The pH
scale
ranges
from 0 to
14.
• The pH
of pure
water is
7.
• Substances added to water can lower
or raise the pH.
• A solution with a pH below 7 is acidic.
• A solution with a pH above 7 is basic.
• Organisms can tolerate only small
changes in pH because every cell
has a particular pH at which it
functions best.
• For example, changes in pH cause
changes in the shapes of enzymes,
resulting in a change in their activity.
Public Health
• In the past, streams
and rivers were
often used to
dispose of human
waste.
• These were called
open sewers.
• This led to disease and
contamination of drinking water.
•Advances in water treatment and
sanitary sewers have helped to
eliminate diseases from our waters.
Humans can live without food for
more than two months, but cannot
live for more than a week without
water.
No
=
• Clean, fresh
water is essential
for life.
• We must protect
our water
sources from
pollution!!!!
Properties of Water Video
• http://dirpy.com/studio/0eNSnj4ZfZ8?q=
properties%20of%20water
Fun Lecture Additions!
• pH video:
– http://dirpy.com/studio/A_URRb5mk5Q?q=
acids%20and%20bases
• Mantis Shrimp comic strip:
– Complements of one of your classmates!
– http://theoatmeal.com/comics/mantis_shri
mp