Ch. 3 Reading Quiz
1.
What are the bonds BETWEEN water
molecules called? Hydrogen bonds
2. What CAUSES hydrogen bonding? polarity
3. What does it mean to be hydrophilic? Attracted
to water
4. Anything with a pH of 0 – 6 is known as a what?
acid
5. Anything with a pH of 8 - 14 is known as a
what?
base
1.
Describe how water contributes to life.
• Life on earth probably
evolved in water
• Living cells are 70 –
95% water
• Water covers ¾ of
earth
• Water exists naturally
in it’s 3 states on
earth – solid, liquid,
gas 
Prizes from yesterday…
2. Describe the structure and geometry of a
water molecule, and explain what properties
emerge as a result of this structure.
• Polar bonds and asymmetrical shape give
opposite charges
• 2 “corners” are occupied by hydrogens
• 2 “corners” have unshared pairs of
electrons
• Oxygen is so electronegative that the
atoms have partial charges 
3. Explain the relationship between the polar
nature of water and its ability to form
hydrogen bonds.
• Polar molecules are held together by H
bonds
• The + charged hydrogen atom is attracted
to the – charged oxygen
• Each water molecule can form a maximum
of 4 hydrogen bonds with other water
molecules 
4. List the characteristics of water that are
emergent properties resulting from hydrogen
bonding.
1. Cohesive behavior
2. Resists temperature change
3. High heat of vaporization & cools as
it evaporates
4. Expands when it freezes
5. Is a versatile solvent 
5. Describe the biological significance of the
cohesiveness of water.
• Cohesive/cohesion = the phenomenon of a
substance being held together by hydrogen
bonds
• Enough hydrogen bonds are in water at any
given time to give water more structure
than other liquids
• Contributes to transport in PLANTS;
adhesion of water the vessel walls
counteracts gravity – forms ‘capillary
action’ 
6. Distinguish between heat and temperature.
Heat
• Total kinetic
energy due to
molecular motion in
a body of matter
Temperature
• Measure of heat
intensity due to
the average kinetic
energy of
molecules in a body
of matter 
7. Explain how water’s high specific heat, high heat
of vaporization and expansion upon freezing affect
both aquatic and terrestrial ecosystems.
Specific Heat
• 1 cal/ g/ ‘C
•Allows a large body
of water to act as a
‘heat sink’; provides
a stable
temperature &
environment
•Ex: desert vs.
coast climates
Heat of
Vaporization
Expansion upon
freezing
• the amount of
heat a liquid must
absorb to have 1 g
become gaseous
• moderates
climate, stabilizes
temperature, allows
for evaporative
cooling
• water is densest
at 4’C
•Expansion due to H
bonds getting
further apart
•Allows for ice to
float – lakes don’t
freeze solid (acts
as insulation)
8. Explain how the polarity of the water
molecule makes a versatile solvent.
(hydrophilic vs. hydrophobic)
Hydrophilic
Hydrophobic
• Charged regions of
polar water molecules
have an electrical
attraction to charged
ions (an affinity for
other polar molecules)
• Nonpolar compounds
(have a symmetrical
distribution of charge)
• Are NOT water
soluble 
9. Define molarity and list some advantages
of measuring substances in moles.
• Molarity – number of moles of solute per liter of
solution
• Advantages –
1. upscales weighing of single molecules from
daltons to grams
2. A mole (mol) of one substance has the same
number of molecules as a mole of any other
substance (6.02 x 1023)
3. Allows one to combine substances in fixed
ratios of molecules 
10. Write the equation for the dissolution of
water, and explain what is actually
transferred from one molecule to another.
H2O + H2O  H3O+ + OH(waters)
(hydronium ion)
(hydroxide ion)
• Only a H+ ion is actually transferred; it binds to
the unshared orbital of the 2nd H2O molecule
making H3O+
• Is expressed as the dissociation into H+ and OH• The reaction is reversible
• At equilibrium, most H2O is not ionized
• Only 1 out of 554,000,000 H2O molecules are
dissociated 
11. Explain the basis for the pH scale, and
describe how acids and bases affect the
hydrogen ion concentration of a solution.
• pH scale is used to measure the degree of
acidity 0-14
• Strong acids and bases dissociate completely
in water
(Ex: NaOH  Na+ + OH- ; HCl  H+ + Cl- )
• Acids increase the relative [H+] in a solution
• Bases reduce the relative [H+] in a solution
[H+] = [OH-] in a neutral solution
[H+] > [OH-] in an acidic solution
[H+] < [OH-] in a basic solution 
12. Using the bicarbonate buffer system as
an example, explain how buffers work.
H2CO3  HCO3 + H+
(H+ donor, w.a.)
(H+ acceptor, w.b.) (ion)
• Buffer = a substance that minimizes large sudden
changes in pH
- works by accepting H+ ions from solution where
there is excess and donates H+ ions to the solution
where they are depleted
Acid ex:
Base ex:
(s.a.) (buffer)
(w.a.)
HCl + NaHCO3  H2CO3 + NaCl
NaOH + H2CO3  NaHCO3 + H2O
(s.b.) (buffer)
(w.b.)

13. Describe the causes of acid
precipitation, and explain how it adversely
affects the fitness of the environment.
Acid precipitation = rain/snow/fog more strongly acidic that
pH 5.6 (lowest recorded 1.5 in VA)
Causes = 1. Sulfur & nitrogen oxides in atmosphere
react w/H2O to form acids
2. Major source is fossil fuel combustion
Effects = 1. Lowers soil pH & affects mineral solubility
(may leach out nutrients and increase
toxicity)
2. Lowers pH of lakes, runoff carries bad soil
into aquatic ecosystems
Ex: Adirondack Mtns with lakes pH <5 = no
fish! 