Chapter 3 - Fall 08

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Chapter 3

Water and the Fitness of theEnvironment

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Outline - Water

Polarity of water

Hydrogen bonding

Properties of water

Temperature moderation by water

Solvent of life Dissociation of Water

Changes in pH

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Water - Polarity

Water simple! common! but e"ceptional

H#$ two Hydrogen and one $"ygen

covers %&' of earth(s surface

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Water - Polarity

Polar bonds between $ and two H atoms

$"ygen is more electronegative

in water!

$ is ) *slightly negative charge+

H are ), *slightly positive charge+

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-ig. #./0 Polar covalent bonds in a watermolecule

+ +H H

O

H2OPartial positive Partial positive

Partial negative

The two ends of the molecule have opposite charges

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Hydrogen onds

Partial charges on atoms in water allowbonds to form between molecules

Hydrogen !onding

results when H from one molecule is

attracted to $ of a different molecule

partial positive attracted to partial

negative

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Water Polarity

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Hydrogen!ond

H

+H

O

))

))

++

+

Fig( 3(2 Hydrogen !onds

!et*een *ater mole'ules

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Fig( 2(, " hydrogen !ond !et*een *ater and ammonia

+

+

+

+

+

Water H2O.

"mmonia /H3.

Hydrogen !ond

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Water - Polarity

Hydrogen onding

between water molecules

gives water its special properties

Cohesion

"dhesion

&urfa'e 0ension

0emperature 1oderation

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Water Properties - Cohesion

Cohesion

1inding together of li2e molecules by H

bonds

High in water

Hbonds constantly brea2ing and reforming

3ost water molecules are bonded to

neighboring molecules at any instant

Contributes to water transport in plants

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Water Properties - "dhesion

"dhesion

Clinging of one substance to another! for

e"ample! between water and plant cell walls

4lso involves Hbonds

4lso contributes to water transport in plants

Water adheres to molecules of the walls of

the "ylem vessels in plant stems *trun2s+

helps counter the effects of gravity

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Water-'ondu'ting

'ells

"dhesion

Cohesion

$ m

4ire'tion

of *ater

movement

Fig( 3(3 Water

0ransport inplants

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Water Properties
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Water Properties - &urfa'e 0ension

&urfa'e 0ension

3easure of how

difficult it is to stretch

or brea2 the surfa'eof a li5uid

Higher in water than

other li5uids

$rdered

arrangement of

water molecules at

airwater interface-ig 0.6 Wal2ing on Water

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Water

Polarity of water

Hydrogen bonding

Properties of water

0emperature moderation !y *ater

Solvent of life

Dissociation of Water

Changes in pH

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Water - 0emperature 1oderation

Heat is the measure of the total amount of

2inetic energy *energy of motion+ in a body of

matter

0emperatureis a measure of the intensity of

heat due to the average2inetic energy of the

molecules

How does water moderate temperature7

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Water can absorb a lot of heat with only a

small change in temperature

has a high &pe'ifi' Heat

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Water - &pe'ifi' Heat

4mount of heat that must be absorbed orlost for /g of that substance to change

temperature by /8C

-or water

/ calorie of heat raises / gram /8C

-or ethanol

9.: calorie of heat raises / gram /8C -or iron

9./ calorie of heat raises / gram /8C

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Water(s high specific heat

4llows it to minimi;e temperature

fluctuations to within limits that permit life

Due to hydrogen bonding of molecules

Heat is absorbed when hydrogen bonds

brea2

Heat is released when hydrogen bonds

form

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Significance

4 large body of water can absorb a largeamount of heat from the sun in daytimeand during the summer! while warmingonly a few degrees

4t night and during the winter! the warm

water will warm cooler air

Stabili;es temperatures

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Water - Heat of 6apori5ation

Water(s high heat of vapori;ation

due to H bonding

results in >evaporative 'ooling?

Hottest molecules evaporate! cooler

molecules remain behind

Cools oceans in tropics

@vaporation of sweat cools body

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Fig 3(, Hydrogen !onds in i'e

4re more >ordered? than in li5uid water!

ma2ing ice less dense

Ansulates the water it floats on

Hydrogen

!ond7i8uid *ater

Hydrogen !onds !rea9 and re-form:'e

Hydrogen !onds are sta!le

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Water Properties

Polarity of water

Hydrogen bonding

Cohesion of water molecules

Temperature moderation by water

&olvent of life

Dissociation of Water

Changes in pH

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Water - &olvent of 7ife

Solution

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&olvent dissolving agent *water+

&olute substance that is dissolved

*sugar+

"8ueoussolution water is the solvent

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What happens when a solute dissolves in a

solvent7

Partial negative *$+ and positive *H+ charges

on water molecule have affinity for positive

and negative parts of solute

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-ig 0.: 4 crystal of table salt dissolving in water

Pos. charged a,ions

cling to partial neg.charged $ atoms

of water molecules

eg. charged Clions cling to partial pos.

charged H atoms

of water molecules

Hydration shellsphere of water

molecules

surrounding each

dissolved ion

a,

Cl

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$ther compounds besides ionic ones can

also be solubili;ed

3ost will have regions that are polar

Partial pos. and neg. regions *li2e water+

3ay have some ionic regions! too

Proteins! D4! etc

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Two categories of substances Hydrophili' *waterloving+

compound with an affinity for water

polar or ionic compounds can form Hbonds with water

Hydropho!i'*waterfearing+

compounds which lac2 an affinity for water nonpolar compounds

lipids of the cell membrane

no Hbonding with water

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Fig( 3(; " *ater-solu!le protein

a. 7yso5yme mole'ule in anona8ueous environment

!. 7yso5yme mole'ule purple. in an a8ueous environment

'. :oni' and polar regions on the protein

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Solutes are dissolved in solvent *water+

How are 'on'entrationsof solutes

calculated7

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Water - &olute Con'entrations

Can(t weigh individual molecules

Ese units termed moles

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&olute Con'entration - 1oles

3ole *mol+

the mole'ular *eightof a substance! but

in grams

Water H#$ #*/+ , /: F /=! so /= gGmol

sucrose C/#H

##$

// F 06# gGmol

/#*/#+ , ##*/+ , //*/:+ F 06# gGmol

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3ole *mol+

umber of molecules in

a mole is constant

:.9## " /9#0molecules G mol

4vogadro(s number

4madeo 4vogadro

http://onsager.bd.psu.edu/~jircitano/avogadro.html

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3ole

:.9## " /9#0molecules G mol

Substance 3ol. Wt. 4mt molecules

4 /9 gGmol /9g :.9## " /9#0

1 /99 gGmol /99g :.9## " /9#0

ethyl alcohol 6: gGmol 6:g :.9## "

/9#0

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Water - &olute Con'entration

How are concentrations of solutescalculated7

Ese 1olarity

3 F number of moles of solute

liter of solution

Solutions of the same molarity will have

e5uivalent numbers of molecules *atoms! ions!

etc.+

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4isso'iation of Water

Hydrogen atom shared between two watermolecules may shift from one molecule to

the other

Hydroniumion H

3O+.

Hydro=ideion OH.

2H2O

H

HH

H

H

HH

H

OOOO

Hydrogen bond

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H2$ H+ , $H


Can simplify previous e5uation to

Hydrogen

ionHydro"ide

ion

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H2$ H+ , $H

Hydrogen

ion

Hydro"ide

ion


Ieversible reaction

An e5uilibrium! but mostly H#$ JH,K and J$HK F /9 %3

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"'ids and ases > pH

An pure H#$! JH,K and J$HK F /9%3

How can an imbalance of JH,K and J$HK

occur7

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"'ids and ases > pH

How can an imbalance of JH,K and J$HK occur7

"'id

substance that in'reasesthe H,

concentration in solution

ase

substance that redu'esthe H,

concentration in solution

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"'ids and ases > pH

"'id

Hydrochloric acid in water

HCl H, , Cl

ase

Sodium Hydro"ide in water

a$H a, , $H

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"'ids and ases > pH

ase

Sodium Hydro"ide in water

a$H a, , $H

$Hcombines with H,to form water! thus

lowering J H,K

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"'ids and ases > pH

Wea9 "'ids and ases

Ieversibly release and accept H,

H0 , H, H

6

,

H#C$

0 HC$

0

, H,

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"'ids and ases > pH

Product of JH,K and J$HK F /9/63#

Holds true for any solution

J/9%

3K J/9%

3K F /9/6

3#

for pure water

Af JH,K increases! J$HK decreases

/9% /9% F /9/6

/9& /9L F /9/6

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"'ids and ases > pH

JH,K can vary greatly

by a factor of /99 trillion */9/6+

pH s'aleused to e"press more conveniently

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"'ids and ases > pH

pH s'ale

ranges from 9 to /6

pH F log JH,K

-or neutral solution

pH F log J/9%K F *%+ F %

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"'ids and ases > pH

4cidic solution pH M %

1asic solution pH N %

@ach pH unit represents a /9fold difference

in JH,K

pH &'ale

$

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/eutralsolution

"'idi'solution

asi'solution

OH

OHOH

OH

OHOH

OH

H+

H+

H+

OH

H+ H+

H+ H+

OH

OH

OHOH

H+OH

H+H+

H+

H+H+

H+H+

OH

/eutral

?H+@ A?OH@

:n'reasingly"

'idi'

?H+@B?OH

@

:n'reasing

lyasi'

?H+@C?OH@

$

2

3

D

,

;

attery a'id

astri' Gui'elemon Gui'e

6inegar !eer*ine 'ola

0omato Gui'e

la'9 'offee

Iain*ater

Jrine

&alivaPure *ater

Human !lood tears

&ea*ater

K

$

1il9 of magnesia

Household ammonia

Household!lea'h

Oven 'leaner

2

3

D

-ig. 0.L The

pH scale and

values of somea5ueous

solutions

pH &'ale

$

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/eutralsolution

"'idi'solution

asi'solution

OH

OHOH

OH

OHOH

OH

H+

H+

H+

OH

H+ H+

H+ H+

OH

OH

OHOH

H+OH

H+H+

H+

H+H+

H+H+

OH

/eutral?H+@ A?OH@

:n'reasingly"

'idi'

?H+@B?OH

@

:n'reasing

lyasi'

?H+@C?OH@

$

2

3

D

,

;

attery a'id

astri' Gui'elemon Gui'e

6inegar !eer*ine 'ola

0omato Gui'e

la'9 'offee

Iain*ater

Jrine

&alivaPure *ater

Human !lood tears

&ea*ater

K

$

1il9 of magnesia

Household ammonia

Household!lea'h

Oven 'leaner

2

3

D

-ig. 0.L The pH

scale and values

of somea5ueous

solutions

Oalues for pH

declineas JH,K

increase

Oalues for pH

increaseas

JH,K decreases

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pH > uffers

How can pH changes be minimi;ed7

uffers

Substances that minimi;e changes in JH,K in

solution

Present in all biological fluids

Human blood is maintained at pH %.6

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pH > uffers

How do buffers wor27

accept H,ions from the solution when in

e"cess donate H,ions to the solution when

depleted

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pH > uffers

1icarbonate buffer blood buffer

How it wor2s.

H#C$

0 HC$

0

, H,

Iesponse to

a rise in pH

Iesponse toa drop in pHH,donor

*acid+

H,acceptor

*base+

Hydrogen

ion

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pH > uffers

uffers minimi;e changes in JH,K

Consist of an acidGbase pair to control JH,K

H#C$0G HC$0

carbonic bicarbonate acid ion

Chapter 3 - Fall 08

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Transcript of Chapter 3 - Fall 08