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.

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

1. Cohesion and adhesion2. Moderation of temperature3. Insulation of bodies of water4. 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

“like dissolves like”

Hydrophilic HydrophobicAffinity 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

H2O H3O+ + OH-

(gains proton) H+ + H2O H3O+ (hydronium ion)

(loses proton) H2O – H+ OH- (hydroxide ion)

Dissociation of H2O because of H- bonding

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

• Acid = increases H+ concentration (HCl)

• Base = reduces H+ concentration (NaOH)

• Most biological fluids are pH 6-8

0 7 14

Basic

Acidic

pH Scale

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

Calculating pH

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) = 2Therefore, pH = 2

If [OH-] = 10-10

Then [H+] = 10-4 *****[OH-] + [H+] = 14-log 10-4 = -(-4) = 4Therefore, pH = 4

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•H-bond•unlike-unlike

plants xylembloodveins

Surface Tension•diff. in stretch•break surface•H-bond

Bugs walking on water

Specific Heat

•Absorbs & retains E•Little change to T•H-bond

oceanmod temp protect marine life

Evaporation•liquidgas•KE

CoolingHomeostasis

Universal Solvent•Polarity ionic•H-bond

Good dissolversolvent