Ch. 3 Warm-UpCh. 3 Warm-Up

1.1. What property of water allows a What property of water allows a water strider to water strider to ““walkwalk”” on water? on water?

2.2. Contrast Contrast adhesionadhesion and and cohesioncohesion. . Give an example of each.Give an example of each.

3.3. Contrast Contrast hydrophobichydrophobic and and hydrophilichydrophilic substances. Give an substances. Give an example of each.example of each.

Chapter 3Chapter 3

Water and the Fitness Water and the Fitness of the Environmentof the Environment

You Must KnowYou Must Know

• The importance of hydrogen The importance of hydrogen bonding to the properties of water.bonding to the properties of water.

• Four unique properties of water, Four unique properties of water, and how each contributes to life on and how each contributes to life on Earth.Earth.

• How to interpret the pH scale.How to interpret the pH scale.• The importance of buffers in The importance of buffers in

biological systems.biological systems.

1. Polarity of H1. Polarity of H22OO

• OO-- will bond with H will bond with H++ on a different on a different molecule of Hmolecule of H22O = O = hydrogen bondhydrogen bond

• HH22O can form up to 4 bondsO can form up to 4 bonds

2. Properties of H2. Properties of H22OO

A.A. CohesionCohesion = H-bonding between = H-bonding between likelike molecules molecules

• Surface Tension Surface Tension = measure of how = measure of how difficult it is to break or stretch surface difficult it is to break or stretch surface of liquidof liquid

2. Properties of H2. Properties of H22OO

B.B. AdhesionAdhesion = bonding between = bonding between unlikeunlike molecules molecules

Adhesion of HAdhesion of H22O to vessel walls O to vessel walls counters ↓ pull of gravitycounters ↓ pull of gravity

2. Properties of H2. Properties of H22OO

C. C. TranspirationTranspiration = movement of H= movement of H22O O up plantsup plants

HH22OO clings to each other by clings to each other by

cohesioncohesion; cling to xylem tubes by ; cling to xylem tubes by adhesionadhesion

3. Moderation of 3. Moderation of temperaturetemperatureHeatHeat = Total amount of KE in system = Total amount of KE in system

TemperatureTemperature = measure intensity of = measure intensity of heatheat due to due to averageaverage KE of KE of moleculesmolecules

3. Moderation of 3. Moderation of temperaturetemperatureA.A. WaterWater’’s s high specific heathigh specific heat

• Change temp less when absorbs/loses Change temp less when absorbs/loses heatheat

• Large bodies of water absorb and store Large bodies of water absorb and store more heat more heat warmer coastal areas warmer coastal areas

• Create stable marine/land environmentCreate stable marine/land environment• Humans ~65% HHumans ~65% H22O O stable temp, stable temp,

resist temp. changeresist temp. change

3. Moderation of 3. Moderation of temperaturetemperatureB.B. Evaporative CoolingEvaporative Cooling

Water has high heat of vaporizationWater has high heat of vaporization Molecules with greatest KE leave as Molecules with greatest KE leave as

gasgas Stable temp in lakes & pondsStable temp in lakes & ponds Cool plantsCool plants Human sweatHuman sweat

3. Moderation of 3. Moderation of temperaturetemperatureC.C. Insulation by iceInsulation by ice – –

less dense, floating less dense, floating ice insulates liquid ice insulates liquid HH22O belowO below

Life exists under Life exists under frozen surface frozen surface (ponds, lakes, (ponds, lakes, oceans)oceans)

Ice = solid habitat Ice = solid habitat (polar bears)(polar bears)

4. Solvent of life4. Solvent of life

• SolutionSolution = liquid, homogeneous = liquid, homogeneous mixture of 2+ substancesmixture of 2+ substances

• SolventSolvent = dissolving agent = dissolving agent (liquid)(liquid)

• SoluteSolute = dissolved substance = dissolved substance• Water = versatile solventWater = versatile solvent

4. Solvent of life4. Solvent of life

• ““like dissolves likelike dissolves like””

Hydrophilic Hydrophobic

Affinity for H2O Repel H2O

Polar, ions Nonpolar

Cellulose, sugar, salt

Oils, lipids

Blood Cell membrane

Figure 3.8 A water-soluble proteinFigure 3.8 A water-soluble protein

5. Acids and Bases5. Acids and Bases

HH22O O H H++ + OH + OH--

(gains proton) H(gains proton) H++ + H + H22O O HH33OO++ ( (hydronium hydronium ionion))

(loses proton) H(loses proton) H22O – HO – H++ OHOH-- ((hydroxide ionhydroxide ion))

5. Acids and Bases5. Acids and Bases

• AcidAcid = increases H= increases H++ concentration concentration (HCl)(HCl)

• BaseBase = reduces H= reduces H++ concentration concentration (NaOH)(NaOH)

• Most biological fluids are pH 6-8Most 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 solutionsFigure 3.10 The pH scale and pH values of some aqueous solutions

Calculating pHCalculating pH

[H[H++][OH][OH--] = 10] = 10-14-14

n If [HIf [H++] = 10] = 10-6 -6 M, then [OHM, then [OH--] = 10] = 10-8-8

pH = -log [HpH = -log [H++]]1.1. If [HIf [H++] = 10] = 10-2-2

• -log 10-log 10-2 -2 = -(-2) = 2= -(-2) = 2• Therefore, pH = 2Therefore, pH = 2

2.2. If [OHIf [OH--] = 10] = 10-10-10

• [H[H++] = 10] = 10-4-4

• -log 10-log 10-4 -4 = -(-4) = 4= -(-4) = 4• Therefore, pH = 4Therefore, pH = 4

5. Acids and Bases5. Acids and Bases

BuffersBuffers: minimize changes in concentration : minimize changes in concentration of Hof H++ and OH and OH-- in a solution (weak acids in a solution (weak acids and bases)and bases)

• Buffers keep blood at pH ~7.4Buffers keep blood at pH ~7.4• If blood drops to 7 or up to 7.8, then deathIf blood drops to 7 or up to 7.8, then death

Carbonic Acid – Bicarbonate SystemCarbonic Acid – Bicarbonate System: : important buffers in blood plasmaimportant buffers in blood plasma

HH22COCO33 (carbonic acid) (carbonic acid) HCO HCO33-- (bicarbonate) + (bicarbonate) +

HH++

Ocean acidification threatens coral reef ecosystems

CO2 mixed with seawater Carbonic acid (lowers ocean pH)

The effects of acid precipitation on a forestThe effects of acid precipitation on a forest

H2O Property Chemical Explanation

Examples of 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

bugswater

Specific Heat•Absorbs & retains E•H-bond

oceanmod temp protect marine life

Evaporation•liquidgas•KE

CoolingHomeostasis

Universal Substance

•Polarityionic•H-bond

Good dissolversolvent