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The Chemistry of Life
Properties of Water
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The Water Molecule
Neutral Charge – ZERO
Have no charge
Have an Equal number of p+ and e-
Charges aren’t evenly distributed
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The Water Molecule
Polarity
A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.
(-)
(+)
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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, …)
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Hydrogen Bonds
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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.
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7. 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?
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8. 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
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9. 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
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Ionic Solutions
Na+ ions will be attracted to WHAT END of the water molecule?
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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
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Acids, Bases & pH
1 water molecule in 550 million naturally dissociates into a Hydrogen Ion and a Hydroxide Ion
Hydrogen Ion Hydroxide Ion
Acid Base
H2O  H+ + OH-
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13. How much stronger is a pH3 than a pH of 5?
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… OH-
Each pH unit represents a factor of 10X change in concentration
How much stronger is a pH3 than a pH of 5?
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Acids
Strong Acid = pH 1-3
High in H+ ions
Lower number of OH- ions
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Bases
Strong Base = pH 11 – 14
High in OH-ions
Lower in number of H+ ions
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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 Acid
Weak Base
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