1. Ch. 3 Warm-Up
What property of water allows a water strider to “walk” on water?
Contrast adhesion and cohesion. Give an example of each.
Contrast hydrophobic and hydrophilic substances. Give an example of each.

2. Water and the Fitness of the Environment
Chapter 3
Water and the Fitness of the Environment

3. You Must Know
The importance of hydrogen bonding to the properties of water.
Four unique properties of water, and how each contributes to life on Earth.
How to interpret the pH scale.
The importance of buffers in biological systems.

4. 3.1 Polarity of H2O
O- will bond with H+ on a different molecule of H2O = hydrogen bond
H2O can form up to 4 bonds

5. 3.2 Properties of H2O Cohesion and adhesion Moderation of temperature
Insulation of bodies of water
Great solvent

6. 3.2 Properties of H2O Cohesion = H-bonding between like molecules
H2O neatly bonded to H2O
Allows H2O to be carried up in plants
Surface Tension = measure of how difficult it is to break or stretch surface of liquid
Skin on surface

7. 3.2 Properties of H2O Adhesion = bonding between unlike molecules
Adhesion of H2O to vessel walls counters ↓ pull of gravity

8. 3.2 Properties of H2O
Transpiration = movement of H2O out of plants (evaporation through stomata)
H2O clings to each other by cohesion; cling to xylem tubes by adhesion

9. 3.2 Properties of H2O Moderation of temp
Heat = Total amount of KE in system
Temperature = measure intensity of heat due to average KE of molecules

10. 3.2 Properties of H2O Water has high specific heat
small temp change when absorbs/loses heat
Humans are primarily H2O  stable temp & resist temp changes
Large bodies of water absorb and store more heat  temp change of H2O is small
Release stored heat to warm air at night & winter
Create stable marine/land environment

11. 3.2 Properties of H2O Evaporative Cooling
Water has high heat of vaporization
Molecules with greatest KE leave as gas - vaporize
Stable temp in lakes & ponds
Cool plants down in the sun
Human sweat
H-bonds break between H2O as it heats up on skin, release heat & cools you down as it evaporates
Humidity prevents evaporation of sweat, H2O vapor too high

12. 3.2 Properties of H2O Insulation by ice – less dense, H-bonds
floating ice insulates liquid H2O below
Life exists under frozen surface (ponds, lakes, oceans)
What would happen if ice sank?
Ice = solid habitat (polar bears)

13. 3.2 Properties of H2O H2O = versatile solvent
Solution = liquid, homogeneous mixture of 2+ substances
Solvent = dissolving agent (liquid)
Solute = dissolved substance

14. 3.2 Properties of H2O Hydrophilic Hydrophobic “like dissolves like”
Affinity for H2O
Hatred of H2O
Polar, ions
Nonpolar
Cellulose, sugar, salt
Oils, lipids, wax
Heads of phospholipids
Tails of phospholipids

15. Figure 3.8 A water-soluble protein

16. 3.3 Acids and Bases
Dissociation of H2O because of H- bonding
H2O H3O+ + OH- (gains proton) H+ + H2O  H3O+ (hydronium ion) (loses proton) H2O – H+  OH- (hydroxide ion)

17. 3.3 Acids and Bases
[OH] and [H] in H2O are equal but addition of solutes can disrupt this balance
HCl  H+ + Cl-
NaOH  Na+ + OH-

18. 3.3 Acids and Bases 7 14 Basic Acidic pH Scale
Acid = increases H+ concentration (HCl)
Base = reduces H+ concentration (NaOH)
Most biological fluids are pH 6-8 7 14
Basic
Acidic
pH Scale

19. Figure 3.10 The pH scale and pH values of some aqueous solutions

20. Calculating pH pH = -log [H+] -log 10-2 = -(-2) = 2 Therefore, pH = 2
If [H+] = 10-6 , then [OH-] = 10-8
then [H+][OH-] = x =
pH = -log [H+]
If [H+] = 10-2
-log 10-2 = -(-2) = 2
Therefore, pH = 2
If [OH-] = 10-10
Then [H+] = *****[OH-] + [H+] = 14
-log 10-4 = -(-4) = 4
Therefore, pH = 4

21. H2CO3 (carbonic acid)  HCO3- (bicarbonate) + H+
3.3 Acids and Bases
Buffers: minimize changes in concentration of H+ and OH- in a solution (weak acids and bases)
Buffers keep blood at pH ~7.4
If blood drops to 7 or up to 7.8, then death
Carbonic Acid – Bicarbonate System – regulates blood pH
H2CO3 (carbonic acid)  HCO3- (bicarbonate) + H+
CO2 reacts with H2O in the blood
Carbonic acid dissociates  [H+] and HCO3 removes excess H+
Excess HCO3 then carbonic acid dissociates

22. Ocean acidification threatens coral reef ecosystems
CO2 mixed with seawater  Carbonic acid (lowers ocean pH)

23. The effects of acid precipitation on a forest

24. H2O Property Chemical Explanation Benefits to Life Cohesion polar
H-bond
like-like
↑gravity plants, trees
Adhesion
unlike-unlike
plants xylem
bloodveins
Surface Tension
diff. in stretch
break surface
Bugs walking on water
Specific Heat
Absorbs & retains E
Little change to T
oceanmod temp protect marine life
Evaporation
liquidgas KE
Cooling
Homeostasis
Universal Solvent
Polarity  ionic
Good dissolver
solvent