Chemistry of Life
Chemistry of Life Outline
I. Properties of Water
A. Cohesion, Adhesion, and Surface Tension
B. Temperature Effects
C. Solvent Properties
II. Acids and Bases
A. Properties
B. pH Scale
C. Buffers
D. Salts
Water, Water, Everywhere
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Of all the common molecules on earth, only water
exists as a liquid at the relatively cool temperatures on
the earth’s surface
¾ of the earth’s surface is water, 2/3 of the human body
is water
All organisms require water
Water is essential for cell structure and function, water
participates in many chemical reactions necessary to
sustain life
Water is the only common substance to exist in the
natural environment in all three physical states of
matter-solid liquid and gas
Polar Structure of Water
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Water is a polar molecule: opposite ends of
the molecule have opposite charges
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–
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Recall that the oxygen end of the molecule has a
partial negative charge while the hydrogens have a
partial positive charge
Recall this leads to formation of hydrogen bonds
between water molecules
Water is one of the most polar molecules
known
Cohesion, Adhesion, and Surface
Tension
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Cohesion:
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Adhesion:
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Cohesion and adhesion responsible for Giant
Redwoods
Surface Tension:
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Temperature Effects
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Heat:
–
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KE: energy of motion-atoms and molecules have
KE because they are always moving, faster the
molecule moves, the more KE it possesses
Temperature:
Temperature Effects
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Specific Heat:
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Water has high specific heat which means it
resists changes in temperature (water must
gain or lose more heat for temperature to
change)
Temperature Effects
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Water has a high heat of vaporization-
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Water is one of the few substances that are
less dense as a solid than as a liquid.
Euphausid shrimp under ice
Solvent Properties of Water
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Solvent:
Water is not a universal solvent (think oil and
water) but it is very versatile
Polarity plays an important role in water’s
solvent capabilities
Solute:
Aqueous Solution:
Solvent Properties of Water
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Water can form a hydration shell around some
non-ionic molecules too, by surrounding
individual molecules and interacting with polar
regions of a molecule
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E.g. sugar
Many different kinds of polar compounds, and
ions are dissolved in the water of such
biological fluids as blood, the sap of plants, the
liquid within all cells
Solvent Properties of Water
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Hydrophilic:
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Hydrophobic:
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E.g. mix salad oil with water—shake to break H bonds
but as these bonds reform between water molecules,
they push the oil molecules out of the way-the oil tends
to cluster together in drops or as a layer on the water’s
surface-thereby exposing less surface area to the water
Acids and Bases
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When large molecules are put together or
pulled apart, hydrogen and/or water is very
often involved
When a hydrogen is stripped away from a
covalent bond it leaves as an ion H+ (called a
hydrogen ion), if it is stripped from a water
molecule it leaves OH- a hydroxide ion
Covalent bonds of water often break
spontaneously-ionization
–
H2O → H+ + OH-
Acids and Bases
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Acid:
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Base:
pH Scale
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Changes in acidity (or basicity) due to an
increase or decrease in hydrogen ions are
measured with the pH scale
pH scale is used to determine the acidic or
basic nature of a solution compared to pure
water
Pure water has an equal concentration of
hydrogen and hydroxide ions pH = 7
Buffers
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Most cellular functions within the body adapted
to narrow pH range around 7 (neutral)
Buffers:
Salts
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Salt:
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E.g. NaOH + HCl → NaCl + H2O
NaCl remember is an ionic compound which will dissociate in
water to Na+ and Cl-
Ions
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Most important ions: Na+, Mg2+, Ca2+, K+, ClCa2+ alone is involved in: muscle contraction, cell movements,
blood clotting, cell division, nerve function