2. Ch. 3 Reading Quiz What are the bonds BETWEEN water molecules called?
What CAUSES hydrogen bonding?
What does it mean to be hydrophilic?
Anything with a pH of 0 – 6 is known as a what?
Anything with a pH of is known as a what?
Hydrogen bonds
polarity
Attracted to water
acid
base

3. 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 

4. Prizes from yesterday…

5. Polar bonds and asymmetrical shape give opposite charges
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 

7. 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 

8. Resists temperature change
4. List the characteristics of water that are emergent properties resulting from hydrogen bonding.
Cohesive behavior
Resists temperature change
High heat of vaporization & cools as it evaporates
Expands when it freezes
Is a versatile solvent 

9. 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’ 

11. 6. Distinguish between heat and temperature.
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 

12. Expansion upon freezing
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
the amount of heat a liquid must absorb to have 1 g become gaseous
moderates climate, stabilizes temperature, allows for evaporative cooling
Expansion upon freezing
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)

14. 8. Explain how the polarity of the water molecule makes a versatile solvent. (hydrophilic vs. hydrophobic)
Hydrophilic
Charged regions of polar water molecules have an electrical attraction to charged ions (an affinity for other polar molecules)
Hydrophobic
Nonpolar compounds (have a symmetrical distribution of charge)
Are NOT water soluble 

16. Molarity – number of moles of solute per liter of solution
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 

17. 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 

18. 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 

20. (H+ donor, w.a.) (H+ acceptor, w.b.) (ion)
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
(s.a.) (buffer) (w.a.)
Acid ex: HCl + NaHCO3  H2CO3 + NaCl
Base ex: NaOH + H2CO3  NaHCO3 + H2O
(s.b.) (buffer) (w.b.) 

21. 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! 