Chapter 3: Water and the Fitness of the Environment
Water Molecules and H bonding
A. Electronegative O pulls shared electrons toward itself (-)
away from H nuclei
B. Polar molecule: Opposite charges on opposite sides
1. Properties of water arise from attractions between
polar molecules
4 Properties of Water
I. (1) Cohesion of water molecules
1. Stick together as a result of H bonding
2. Form, break, reform frequently
a. More structure than other liquids
B. Cohesion: H bonds holding substance together
1. Transports against gravity
a. Helps hold together the column of water within
the vessel
b. Xylem vessels
C. Adhesion: The clinging of one substance to another
D. Surface Tension: A measure of how difficult it is to
stretch or break the surface of a liquid
1. Examples:
2. Basilisk lizard: Native of Central and South America
II. (2) Stabilizes air temp
A. Absorbs heat from air that is warmer and releases stored
heat into air that is cooler
B. Heat and Temperature
1. Kinetic energy: Energy of motion
2. Heat: Total quantity of kinetic energy due to
molecular motion in a body of matter
3. Temperature: Measures the intensity of heat due to
the average kinetic energy of the molecules
1
a. Heat and temp are not the same
b. Heat passes from warmer ----> cooler until the
2 are the same temp
4. calorie (cal)
a. Amt. of heat energy it takes to raise 1 g of
water 1oC
b. Amt. of heat energy 1 g of water releases when
cooled 1oC
.
5.Kilocalorie (kcal): 1000cal
a. Quantity of heat required to raise temp of 1 kg
of water by 1oC
b. Food labels
C. Specific heat: The amt of heat that must be absorbed or
lost for 1 g of that substance to change its temp by 1oC
1. Water: 1 cal/go/C (unusually high)
2. Due to high specific heat: changes temp less when it
absorbs or loses heat:
a. Specific heat can be thought of as a measure of
how well a substance resists changing its
temperature when it absorbs or releases heat
D. Due to H bonding
1. Heat must be absorbed to break H bonds
2. Heat is released when H bonds form
a. Ocean temp is stable:
1.
2.
3. Organisms are able to resist changes in their own
temps than if they were made of a liquid with a lower
specific heat
E. Evaporative Cooling
2
1. Vaporization or Evaporation: Transformation
from liquid to gas
a. Molecules move fast enough to overcome
attractions
b. If liquid is heated: Average KE increases
2. Heat of vaporization: Quantity of heat a liquid
must absorb for 1 g of it to be converted from liquid
to gas
a. Water: High heat of vaporization
1.580 cal needed to vaporize 1 g of
water
2.Double that of ammonia or
alcohol
3.Due to H bonding
b. Helps moderate earth’s climate
1.Large amount of solar heat
absorbed by tropical seas
2.Tropical air circulates pole-ward
a.Released as heat as it
condenses to form rain
F.Evaporative cooling: As a substance evaporates, the surface
of the liquid that remains behind cools down
a. The hottest molecules (greatest KE) are most likely to
leave as gas
b. Contributes to stability of temp in lakes and ponds
c. Provides mechanism that prevents terrestrial organisms
from overheating
1. Transpiration
2.Sweating
IV. Oceans and lakes don’t freeze solid because ice floats
3
A. Water is less dense as a solid than as a liquid
1. At temps above 4oC water behaves like other liquids
a.Expanding when it warms
b.Contracting when it cools
2. Begins to freeze when its molecules are no longer
moving vigorously enough to break H bonds
1.0oC: Becomes locked into a crystalline lattice
2. Each water molecule bonded to a max of 4
partners
3. H bonds keep molecules at “arm’s length”
a. Far enough apart to make ice about 10%
less dense than water at 4oC
1.10% fewer molecules for the same
volume
4.When ice absorbs enough heat for it’s temp to
increase above 0oC
a. H bonds between molecules are disrupted
b. As crystal collapses, ice melts, molecules
are free to slip closer together
c. Greatest density at 4oC then expands as
molecules move faster
d.(Liquid water is semi-structured because of
H bonds)
A. Fitness of environment
1. If ice sank, eventually lakes, ponds, and oceans would
freeze solid
a. During summer: Only a few inches of ocean would
thaw
b. When a deep body of water cools
a. Floating ice insulates liquid water below it
1. Protects from colder air
4
2.Krill below Antarctic ice
V. Water is the solvent of life
A. Solution: A liquid that is a homogeneous mixture of 2 or
more substances
1.Uniform mixture of sugar and water
2.Solvent: Dissolving agent of a solution
3.Solute: Substance that is dissolved
4.Aqueous solution: One in which water is the solvent
B. Water is not the univ V. Water is the solvent of life
A. Solution: A liquid that is a homogeneous mixture of 2 or
more substances
1.Uniform mixture of sugar and water
2.Solvent: Dissolving agent of a solution
3.Solute: Substance that is dissolved
4.Aqueous solution: One in which water is the solvent
5. Colloid: A stable suspension of fine particles in a
liquid
a. Molecules too large to dissolve
B. Versatile solvent: Due to its polarity
1. Ionic compound dissolve in water
a. Hydration Shell: Sphere of water molecules
surrounding individual cation and anions
b. Result: Solution consisting of 2 solutes
c. Sea water and human cells
2. Polar compounds are water soluble
a. Sugars (Water coats polar sugar molecules)
b. Large proteins
1. Ionic and polar regions on the surface
5
2. Ex: Lysozyme
c. Many kinds of polar compounds and ions are
dissolved in biological fluids
1. Blood, sap, liquid within cells
2. Water is the solvent of life
C. Hydrophilic and Hydrophobic Substances
1.Hydrophilic: Any substance that has an affinity for
water
a. Hydro: Water (Greek)
b. Philios: Loving
c. Term is used even if substance does not
dissolve because the molecules are too large
1. Cotton Towel
2.Hydrophobic: Substances that neither dissolve nor
have an affinity for water
a. Seem to repel water
b. phobos: Fearing
c .Non ionic, non-polar substances
1. Vegetable oil and water
2. Nonpolar bonds: Particularly bonds
between C and H
a. Hydrophobic molecules are major
ingredients of cell membranes
D. Solute Concentration in Aqueous Solutions
1. Mole (mol):
2. Molecular mass: Sum of masses of all atoms in a
molecule
3. Avagadros number: The number of molecules or
atoms in a mole
a. Sucrose (C12H22O11) =
b. Ethyl alcohol (C2H6O)=
6
4. Making a Liter of solution
a. 1 mol of solute dissolved in enough water to
make a Liter of solution
b. One-molar solution (1 M)
b. Molarity: The number of moles of solute per
liter of solution
VI. Organisms are sensitive to changes in pH
A. Dissociation (separation) of Water Molecules
1. Hydrogen ion (H+): A single proton with a charge
of +1 is transferred
a. Hydronium ion (H3O+)
2.Hydroxide ion (OH-): Water molecule that lost a
proton (–1)
B. Acids and Bases
1. Dissociation of water produces one H+ for every OHa. Concentrations of these ions will be equal in pure
water
b. 10-7 M (at 25oC)
i. Only one ten-millionth of a mole of H
ions/L of pure water
ii. Equal # of OH- ions
c. What would cause an aqueous solution to have an
imbalance in H+ and OHa. Acid: A substance that increases H+
concentration of a solution
b. Base: A substance that reduces H+
concentration in solution
1. Indirectly: Dissociate to form OH- that
combine with H+ ions to form water
7
2. Reduce H+ directly by accepting H+
ions
3. Neutral: solution: H+ and OH- ions are
neutral
Single arrows:
Double arrows:
a. Weak acids: Dissociate reversibly
to release and reaccept H+ ions
H2CO3  HCO3- + H+
b. Weak base
C. pH Scale: A measure of H+ concentration equal to
log[H+] and ranging in value from 0 to 14
1. For a neutral solution: -log 10-7 =
2. PH of neutral solution: 7
a. Each pH unit represents a tenfold difference in
H+ and OH- concentrations
3. Buffers: Substances that minimize changes in the
concentrations of H+ and OHa. Blood: pH: 7.4
b. Buffers accepts H+ from solution when they are
in excess and donating H+ when they have been
depleted
1. Weak acids or bases that combine
reversibly with H+
c. Equilibrium between carbonic acid and
bicarbonate acts as a pH regulator
8
VII. Acid Precipitation: Refers to rain, snow, or fog more acidic
than pH 5.2
A. Uncontaminated rain: pH of 5.6
C. Caused by sulfur oxides and nitrogen oxides that react
with water in air to form acids
1. Fall to earth as rain or snow
2. Source: Combustion of fossil fuels by factories and
automobiles
3. Prevailing winds carry clouds
C. Harms both terrestrial and freshwater ecosystems
1. Lowers pH of soil solution
a. Affects solubility of minerals
b. Other minerals reach toxic concentrations
2. Lowered pH of lakes and ponds
D. Can be reduced through industrial controls and antipollution devices
1. Clean Air Act of 1990
9