1. Water and the Fitness of the Environment
Chapter 2
Water and the Fitness of the Environment

2. Polarity of Water Water is a polar molecule
Hydrogen of one H2O is attracted to the Oxygen of another H2O
Therefore, hydrogen bonding occurs

3. Properties of Water
Water has 4 properties that make Earth a fitting environment for life:
High surface tension/Cohesive behavior
Ability to stabilize temperature
Expansion upon freezing
Versatility as a solvent for life

4. 1. Cohesion
Cohesion:
Hydrogen bonds hold water together in liquid form
Responsible for transport of water against gravity in plants

5. Cohesion Adhesion = clinging of one substance to another
Cohesion = adhesion of water to itself
Surface Tension = how hard it is to stretch or break the surface of a liquid

6. 2. Ability to Stabilize Temperatures
Water…
Absorbs heat from air that is warmer than itself
Releases stored heat to air that is cooler than itself

7. Ability to Stabilize Temperatures
Water’s high specific heat
Specific heat
amount of heat that must be absorbed or lost for 1g of that substance to raise its temperature by 1C
Because of its high specific heat (due to hydrogen bonding) water resists temperature change
LOTS of hydrogen bonds have to be broken before water molecules can start moving faster

8. Ability to Stabilize Temperatures
Application:
Large body of water can absorb LOTS of heat from the sun
Then, the gradually cooling water warms the air at night and in the winter
Mild climate of coastal areas
Ocean, lake, pond temperatures remain stable – IMPORTANT!

9. 3. Expansion Upon Freezing
Water is less dense as a solid than as a liquid:
Because of hydrogen bonding! 
Therefore, ice floats
Ice:
Each water molecule bonded to max of 4 “partners”
Water:
Bonds are constantly breaking and reforming

10. Expansion Upon Freezing
Application and Importance:
Allows marine life to continue to live even when the top layer of water is frozen
Ice acts as an insulator

11. 4. Solvent of Life Solution: Solvent: Solute:
A liquid that is a homogeneous mixture of 2 or more substances
Solvent:
The dissolving agent
Ie. water
Solute:
Substance that is dissolved
Ie. Kool-aid powder

12. Solvent of Life Aqueous Solution: Water is NOT a universal solvent
A solution in which water is the solvent
Water is NOT a universal solvent
Why not?

13. Solvent of Life Hydrophilic: Hydrophobic: “water-loving”
Polar and ionic compounds
Hydrophobic:
“water-fearing”
Nonpolar compounds

14. The pH Scale The dissociation of water H2O  H+ + OH- In water:

15. The pH Scale Acid: Base:
A substance that increases the H+ concentration of a solution
[H+] > [OH-]
Base:
A substance that decreases the H+ concentration of a solution
[H+] < [OH-]

16. The pH Scale Logarithmic scale of 0 – 14 Neutral pH = 7
Acidic pH = <7
More H+ ions
Basic pH = > 7
Fewer H+ ions
pH declines as H+ concentration increases

17. (Sulfur oxides or nitrogen oxides) + water  acids
Acid Precipitation
pH of normal rain = 5.6
pH of acid rain = as low as 1.5
(Sulfur oxides or nitrogen oxides) + water  acids
Human blood pH = 7.4
7.0 or 7.8 = death!
Importance:
Aquatic animals, plants, etc…