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.

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

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.

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

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

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

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

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

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

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

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

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)

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

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

Figure 3.8 A water-soluble protein

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)

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-

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

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

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

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

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

The effects of acid precipitation on a forest

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