The Chemistry of
Life
Properties of Water
copyright cmassengale
The Water Molecule
• Neutral Charge – ZERO
• Have no charge
• Have an Equal number of p+
and e• Charges aren’t evenly
distributed
copyright cmassengale
The Water Molecule
• Polarity
– A water molecule is polar because
there is an uneven distribution of
electrons between the oxygen and
hydrogen atoms.
(+)
(-)
copyright cmassengale
Hydrogen Bonds
• Polar water molecules act like magnets
and attract each other
• Hydrogen Bonds
– The attraction of the Hydrogen end
(+) of one molecule for the Oxygen
end (-) of another water molecule.
• They are strong bonds that form
between molecules (CO2, H2O, …)
copyright cmassengale
Hydrogen Bonds
copyright cmassengale
Cohesion
• The attraction
between molecules of
the same substance
(e.g. water).
• H2O attracting other
H2O molecules
• Allows some insects
and spiders to walk on
water.
copyright cmassengale
Adhesion & Capillarity
• Adhesion - Attraction between H2O
molecules and different molecules
• Cohesion & adhesion produce
Capillarity (upward movement against
gravity of water through small tubes)
Question: How do
plants make use of
Capillarity?
copyright cmassengale
Solutions & Suspensions
• Water is usually part of a
mixture.
• Because so many things dissolve in
water, it is called the Universal
Solvent
• There are two types of mixtures:
– Solutions
– Suspensions
copyright cmassengale
Properties of Solutions
• Ionic compounds disperse as ions in
water (+ions & -ions spread out among
polar water molecules)
• Solutions are Evenly distributed
mixtures
• SOLUTE
– Substance that is being dissolved
• SOLVENT
– Dissolving Substance for the solute
copyright cmassengale
Ionic Solutions
Na+ ions will be attracted to WHAT END of
the water molecule?
copyright cmassengale
Suspensions
• Substances that
don’t dissolve but
separate into tiny
pieces.
• Water keeps the
pieces suspended
so they don’t
settle out.
• Blood & Cytoplasm
are suspensions
copyright cmassengale
Acids, Bases & pH
• 1 water molecule in 550 million
naturally dissociates into a Hydrogen
Ion and a Hydroxide Ion
H2O 
H+
+ OH
Hydrogen Ion
Acid
copyright cmassengale
-
Hydroxide Ion
Base
The pH Scale
•
•
•
•
•
•
Indicates the concentration of H+ ions
Ranges from 0 – 14
pH of 7 is neutral
pH 0 up to 7  acid … H+
pH above 7 to 14  base… OHEach pH unit represents a factor of
10X change in concentration
How much stronger is a pH3 than a pH of
5?
copyright
cmassengale
Acids
• Strong Acid
= pH 1-3
• High in H+
ions
• Lower
number of
OH- ions
copyright cmassengale
Bases
• Strong Base =
pH 11 – 14
• High in OHions
• Lower in
number of H+
ions
copyright cmassengale
Buffers
• Weak acids or bases that react
with strong acids or bases
• Made by the body
• Prevent sharp, sudden changes in
pH (keep pH neutral)
Weak Acidcopyright cmassengale Weak Base
copyright cmassengale