Biophysical Chemistry
Biophysical Chemistry
PROPERTIES OF WATER PROPERTIES OF WATER
H
2O
A water molecule, is made up of threethree atoms. These are one oxygen and two hydrogen atoms.
Water is polar.
In each water molecule, the oxygen atom attracts moreoxygen atom attracts more than its
"fair share" of electronselectrons
The oxygenoxygen end “acts” negativenegative The hydrogenhydrogen end “acts” positivepositive Causes the water to be polar.polar.
However, Water is neutralneutral (equal number of e- and p+) (Zero Net ChargeZero Net Charge))
Interaction Between Water Molecules Interaction Between Water Molecules
Negative Oxygen Negative Oxygen end of one water molecule is end of one water molecule is attracted to the
attracted to the Positive Hydrogen Positive Hydrogen end of another end of another water molecule to form a
water molecule to form a HYDROGEN BOND HYDROGEN BOND
At sea level, pure water boils at 100 °C and At sea level, pure water boils at 100 °C and
freezes at 0 °C.
freezes at 0 °C.
The boiling temperature of water decreases at The boiling temperature of water decreases at
higher elevations (lower atmospheric higher elevations (lower atmospheric
pressure).
pressure).
For this reason, an egg will take longer to boil For this reason, an egg will take longer to boil
at higher altitudes at higher altitudes
Properties of Water
Properties of Water
Properties of Water Properties of Water
Cohesion Cohesion
Adhesion Adhesion
High Specific Heat High Specific Heat
High Heat of Vaporization High Heat of Vaporization
Less Dense as a Solid Less Dense as a Solid
COHESION COHESION
Attraction between particles of the same Attraction between particles of the same substance (why water is
substance (why water is attracted to itself) attracted to itself)
Results in Surface tension (a measure of the Results in Surface tension (a measure of the strength of water’s surface)
strength of water’s surface)
Produces a surface film on water that allows Produces a surface film on water that allows insects to walk on the surface of water
insects to walk on the surface of water
• Amount of heat needed to raise or lower 1g of a Amount of heat needed to raise or lower 1g of a substance 1° C.
substance 1° C.
• Water resists temperature change, both for Water resists temperature change, both for heating and cooling.
heating and cooling.
• Water can absorb or release large amounts of Water can absorb or release large amounts of heat energy with little change in actual
heat energy with little change in actual temperature.
temperature.
High Specific Heat
High Specific Heat
High Heat of Vaporization High Heat of Vaporization
Amount of energy to convert 1g or a substance from a Amount of energy to convert 1g or a substance from a liquid to a gas
liquid to a gas
In order for water to evaporate, hydrogen bonds must In order for water to evaporate, hydrogen bonds must be broken.
be broken.
As water evaporates, it removes a lot of heat with it. As water evaporates, it removes a lot of heat with it.
High Heat of Vaporization High Heat of Vaporization
Water's heat of vaporization is 540 cal/g. 540 cal/g.
In order for water to evaporate, each gram must GAIN In order for water to evaporate, each gram must GAIN 540 calories (temperature doesn’t change -100
540 calories (temperature doesn’t change -100
ooC). C).
As water evaporates, it removes a lot of heat with it As water evaporates, it removes a lot of heat with it (cooling effect).
(cooling effect).
Water vapor forms a kind of global ‘‘blanket” which Water vapor helps to keep the Earth warm.
Heat radiated from the sun warmed surface of the Heat radiated from the sun
earth is absorbed and held by the vapor. absorbed and held by the vapor
Water is Less Dense as a Solid Water is Less Dense as a Solid
Ice is less dense as a solid than as a liquid (ice Ice is less dense floats)
Liquid water has hydrogen bonds hydrogen bonds that are constantly being broken and reformed
constantly being broken and reformed . .
Frozen water Frozen water forms a crystal-like lattice crystal-like lattice
wherebymolecules are set at fixed distances.
Homeostasis Homeostasis
Ability to maintain a steady state despite changing Ability to maintain a steady state despite changing conditions
conditions
Water is important to this process because:Water is important to this process because:
a. Makes a good insulator a. Makes a good insulator
b. Resists temperature change b. Resists temperature change
c. Universal solvent c. Universal solvent
d. Coolant d. Coolant
e. Ice protects against temperature
e. Ice protects against temperature extremes extremes (insulates frozen lakes)
(insulates frozen lakes)
Solutions
Solutions and and Suspensions Suspensions
Water is usually part of a mixture. Water is usually part of a mixture.
There are two types of mixtures: There are two types of mixtures:
- - Solutions Solutions
- - Suspensions Suspensions
Solution Solution
Ionic compounds disperse as ions in waterIonic compounds disperse as ions in water
Evenly distributedEvenly distributed
SOLUTESOLUTE
* * Substance that is being dissolved Substance that is being dissolved
SOLVENTSOLVENT
* * Substance into which the solute dissolves Substance into which the solute dissolves
Suspensions Suspensions
Substances that don’t dissolve but separatedon’t dissolve but separate into tiny pieces.
Water keeps the pieces suspended so they don’t Water keeps the pieces suspended settle out.
Acids, Bases and pH Acids, Bases and pH
One water molecule
One water molecule naturally dissociatesnaturally dissociates into a into a Hydrogen Ion
Hydrogen Ion (H+) (H+) and a Hydroxide Ion (OH-)and a Hydroxide Ion (OH-)..
Hydrogen Ion Hydroxide Ion Hydrogen Ion Hydroxide Ion
Acid Acid Base Base
H
2O H
++ OH -
The pH Scale The pH Scale
Indicates the concentration of Hconcentration of H++ ions ions
Ranges from 0 – 140 – 14
pH of 7 is neutral7 is neutral
pH 0 up to 7 is acid 0 up to 7 is acid … H+
pH above 7 – 14 is babove 7 – 14 is basic… OH-
Acids Acids
Strong Strong Acids Acids have a pH of have a pH of 1-3 1-3
Produce lots Produce lots
of of H H
+ +ions ions
Bases Bases
Strong Bases Strong Bases have a pH of 11 11 to 14
to 14
Contain lots of lots of OHOH--ionsions and fewer H+ ions
Buffers Buffers
Weak acids or bases that react with strong acids or Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH
bases to prevent sharp, sudden changes in pH (neutralization).
(neutralization).
