WATER Rearrange

8/9/2019 WATER Rearrange

1/71

WATER


2/71

COU RSE OU TCOM E ( C0 1)CO2: Ability to define and describe thebiochemical concepts and terms associatedwith life.Terms used in Course Outcome andTeachingKnowledge: Define , introduce , describe , name , relate , explain , identify and Remember concepts and principles.

R epetition : Repeat and discuss concepts andprinciples.A pplication : Apply , demonstrate , interpret andillustrate concepts and principles.


3/71

*LECTURE CON TE NTS

1. Why water is important to biochem ?2 . USES OF WATER3. PHYSI CS & CHE MISTRY OF WATER4. PHYSI C AL PR OPERTIES OF WATER5. Molecular Structure of Water

6. Hydrogen Bonding7. Polarity of water 8. Noncovalent Bonding9. Weak , van der Waals forces10 . Thermal properties of water 11. Osmosis , reverse osmosis & dialysis12 . Water ionization , pH , titration and buffer 13. Summary14. The end note

S ect


4/71

*Sect 1. Introduction

Why water is important to biochem ?

M ore than 70% of the earths surface iscovered with the molecule of water.Cell components and molecules (protein,

poly sacharides, nucleic acid, membranes)assume their shape in response to water Water acts as a solvent & substrate for many cellular reactionsWater is a common chemical substance that is

essential for the survival of all known forms of life . ( In typical usage, water refers only to its liquid form or state , but thesubstance also has a solid state, ice , and a gaseous state, water vapor . )


5/71


6/71

IntroductionPhysics & Chemistry of water

Water is the chemical substance with chemical formulaH 2 O : one molecule of water has two hydrogen atomscovalently bonded to a single oxygen atom.

Water is a tasteless , odorless liquid at ambienttemperature and pressure , and appears colorless in smallquantities , although it has its own intrinsic very light bluehue.

Oxygen attracts electrons much more strongly thanhydrogen , resulting in a net positive charge on thehydrogen atoms , and a net negative charge on the

oxygen atom.The presence of a charge on each of these atoms giveseach water molecule a net dipole moment .


7/71

Electrical attraction (hydrogen bonding) between water molecules due to this dipole pulls individual moleculescloser together , making it more difficult to separate themolecules and therefore raising the boiling point.

Water can be described as a polar liquid that dissociates

disproportionately into the hydronium ion (H3 O+ (aq)) andan associated hydroxide ion ( OH(aq))

Water is in dynamic equilibrium between the liquid , gasand solid states at standard temperature and pressure(0C , 100 .000 kPa) , and is the only pure substance

found naturally on Earth.


8/71

Introduction

UN IQUE PHYSI C AL PR OPERTIES OF WATER

Exist in all three physical states of matter : solid , liquid , and gas .

Has high specific heatWater conducts more easily than anyliquid except mercury

Water has a high surface tensionWater is a universal solven tWater in a pure state has a neutral p H .


9/71


10/71

Molecular structure of water

The bent structure indicate water is polar coz linear structure is nonpolar.

Phenomenon where charge is separatedto partial ve charge and partial +vecharge is called dipoles.


11/71


12/71

Ionic InteractionsIonic interactions occur between charged atoms or groups.Oppositely charged ions are attracted to eachother.

In proteins , side chains sometimes form ionic saltbridges.

C H 2C H 2CO O -

C H 2C H 2NH 3+

S alt bridge


13/71

Hydrogen Bonding

Water molecules can perform hydrogen bond withone another. Four hydrogen bonding attractionsare possible per molecule :

2 through the

hydrogens and2 through thenonbondingelectron pairs.

HO

H

HO

H

HO

H

HO

HH O H


14/71

Hydrogen Bonding A hydrogen attached to an O or N becomes very polarized and highlypartial plus ( +). This partialpositive charge interacts with thenonbonding electrons on another O giving rise to the very powerfulhydrogen bond.

R1 O H

HO

H

HO

Hhydrogen bondshown in yellow


15/71

Water has an abnormally high boiling pointdue to intermolecular hydrogen bonding.

H

OH

H

H

H HO

H

H

H

H

H

OH

H

H

H H bonding is aweak attractionbetween an

electronegativeatom in onemolecule and an H(on an O) inanother .


16/71

Water molecule with bond ( ) and net( ) dipoles.

H O HH+

H-

H+


17/71


18/71

Van der Waals Attractionsa. Dipole-dipoleb. Dipole-induced dipolec. Induced dipole-induced dipole

C O C OH+H-

H+H-

H

H

HH

H

H

HH

H +H -

H +H -

O H

H

HH

H +H - H +

H -


19/71

Sect 4 : Thermal properties of water Hydrogen bonding keeps water in the liquid phasebetween 0oC and 1 00 oC .

Liquid water has a high :

Heat of vaporization - energy to vaporize one moleof liquid at 1 atmHeat capacity - energy to change thetemperature by 1 oC

Water plays an important role in thermal regulation inliving organisms.


20/71

Relationship between temperature and hydrogen

bondMax number of hydrogen bonds form when water hasfrozen into ice.Hydrogen bonds is approximately 15% break when iceis warmed.Liquid water consists of continuously breaking andforming hydrogen bonds.The rising tempt. The broken of hydrogen bonds areaccelerating.When boiling point is reached , the water moleculesbreak free from one another and vaporize.


21/71

Water easily dissolves a wide variety of the constituents of living organisms.

Water also unable to dissolve somesubstancesThis behavior is called hydrophilic andhydrophobic properties of water.

Sect. 5 : Solvent Properties of Water


22/71

Water is a polar molecule.

A polar molecule is one in which one end ispartially positive and the other partiallynegative.

This polarity results from unequal sharing of

electrons in the bonds and the specificgeometry of the molecule.

Polarity of water


23/71

Hydrophillic substances

dissolve in water The polar nature of water makes it an excellentsolvent for polar and ionic materials that arewater loving (hydophillic)

An ion immersed in a polar solvent such aswater attracts the the oppositely charged endsof the solvent dipoles and becomes surroundedby one or more concentric shells of orientatedsolvent molecules , therby becoming solvated or hydrated when water is the solventThe bond dipoles of uncharged polar moleculesmake them soluble in aqueous solutions.


24/71

HYDR OPH OBIC INTERA CTION S

Nonpolar molecules tend to coalesceinto droplets in water. The repulsionsbetween the water molecules and the

nonpolar molecules cause thisphenomenon.

The water molecules form a cagearound the small hydrophobic droplets.


25/71


26/71

Nonpolar Molecules- 2

Water forms hydrogen-bonded cage like structuresaround hydrophobic molecules , forcing them out of solution.


27/71

Amphipathic Molecules Amphipathic molecules contain both polar andnonpolar groups.

Ionized fatty acids are amphipathic. Thecarboxylate group is water soluble and the longcarbon chain is not.

Amphipathic molecules tend to form micelles , colloidal aggregates with the charged headfacing outward to the water and the nonpolar tailpart inside.


28/71

A Micelle


29/71

Typical Bond Strengths

Type kJ/molCovalent >210

N on-covalent

Ionic interactions 4-8 0

Hydrogen bonds 1 2-30

van der Waals 0 .3-9

Hydrophobic interactions 3-1 2


30/71

Osmosis , Reverse Osmosis & Dialysis

Osmosis is a spontaneous process in which solvent(e.g. water) molecules pass through a semi permeablemembrane from a solution of lower solute (e.g.chemical) concentration to a solution of higher soluteconcentration.

Osmosis is the movement of solvent from a region of high concentration (here , pure water) to a region of relatively low concentration (water containing dissolvedsolute).

Water moves by osmosis and solutes by diffusion.


31/71

OS MOTIC PRESS URE

Osmotic pressure is the pressure required tostop osmosis or the influx of water ( 22 .4 atm for 1M solution).Because cells have a higher ion concentrationthan the surrounding fluids , they tend to pick upwater through the semi permeable cellmembrane.The cell is said to be hypertonic relative to thesurrounding fluid and will burst (hemolyze) if osmotic control is not effected.


32/71


33/71

Definitions of solutions

H ypotonic solution: A solution with a lower salt concentration than in normal cells of thebody and the blood.

Hypertonic solution: A solution with a higher salt concentration than in normal cells of the

body and the blood.

Isotonic solution: A solution that has the same

salt concentration as the normal cells of thebody and the blood. An isotonic beverage maybe drunk to replace the fluid and minerals whichthe body uses during physical activity.


34/71


35/71

Osmotic-pressure formulaT ! iMRT

i = vant Hoff factor (% as ions)M = molarity (mol/ L for dilute solutions)R = (normal gas constant expressed in liters andatmospheres)

0 .082 L atm/ mol KT = Kelvin temperature

O r = i *C*R*T

T= absolute temperature (in Kelvin)R= the gas constant in whatever units you need toexpress osmotic pressure (e.g. if you want in atmthen R= 0 .082 L*atm/(mole *K))C = the concentration of your solute in mole/ L


36/71

i is the van't Hoff coefficient . For non-electrolytes i=1

For strong electrolytes i= the number of ionsthat are produced by the dissociation accordingto the molecular formulae.g for Na C l you have 2 ions (1 Na + and 1 C l-)so i= 2 , for Ca C l2 , 3 ions (1 Ca +2 from 2 C l-) so i=3.

For weak electrolytes , if n is the number of ionscoming from the 1 00 % dissociation according tothe molecular formula and a the degree of dissociation then i=(1- a )+ n a .E.g. if we assume for CH3 COO H a=8 0% i=(1-0 .8) +2 *0 .8= 0 .2+ 1.6=1.8


37/71

Liquids move from high osmotic pressure

(high conc. solvent and low conc. solute) tolow osmotic pressure (high conc. soluteand low conc. of solvent)


38/71

RE VERSE OS MOSIS

R everse osmosis (R O ) is a separation processthat uses pressure to force a solution through amembrane that retains the solute on one sideand allows the pure solvent to pass to the other side.

More formally , it is the process of forcing asolvent from a region of high soluteconcentration through a membrane to a regionof low solute concentration by applying apressure in excess of the osmotic pressure .

It is used in water purification and desalination.


39/71

DIALYSIS

A concentrated solution is separated from alarge volume of solvent by a dialysis membraneor bag that is permeable to both water andsolutes.

Only small molecules can diffuse through thepores of the membrane.

At equilibrium , the concentrations of smallmolecules are nearly the same on either side of

the membrane , whereas the macromolecules , such as proteins or nucleic acids , remain insidethe dialysis bag.


40/71

KIDNEY DIA LYSISReverse osmosis is the technique usedin dialysis , which is used by people withkidney failure.

The kidneys filter the blood , removingwaste products (e.g. urea) and water , which is then excreted as urine .

A dialysis machine mimics the functionof the kidneys. The blood passes fromthe body via a catheter to the dialysismachine , across an osmotic filter.


41/71

Sect 1 2: Water ionization , pH , titration and buffer

The self-ionization of water is the chemical reaction inwhich two water molecules react to produce a hydronium(H3 O +) and a hydroxide ion ( OH ).

Water ionization occurs endothermically due to electricfield fluctuations between molecules caused by nearbydipole librations resulting from thermal effects , andfavorable localized hydrogen bonding.

Ions may separate but normally recombine within a fewmin. to seconds. Rarely (about once every eleven hours

per molecule at 25C , or less than once a week at 0C )the localized hydrogen bonding arrangement breaksbefore allowing the separated ions to return , and the pair of ions (H +, OH-) hydrate independently and continuetheir separate existence.


42/71

Ionization of Water

Water dissociates. (self-ionizes)H2O + H2O = H 3O + + OH-

Kw = K a [H 2 O]2 = [ H 3 O + ][O H -]

Ka = [H3O+][OH-][H2O]2


43/71

Water Ionization- 2The conditions for the water dissociation equilibrium must holdunder all situations at 25o C .

Kw= [H 3O+][OH-]=1 x 1 0-14

In neutral water , [H3O

+ ] = [OH-] = 1 x 1 0-7 M


44/71

Water ionization - 3

When external acids or bases areadded to water , the ion product ([H 3O

+

][OH-] ) must equal Kw.

The effect of added acids or bases is

best understood using the Bronsted-Lowry- theory of acids and bases.


45/71

Bronsted- Lowry definitions An acid i s a subs tance that can donate a pr oton

A base i s a subs tance that can acce pt a pr oton

H+ ions (called a protons , since a H + ion has neither electrons nor neutrons).

This definition can be represented by the general chemicalreaction

A ' B + H+ which does not attempt to show electrical charge balance.In this equation - A is the acid. , B is the base and H+ (a hydrogen atom without an electron) is a proton.


46/71

Conjugate acid/base

An acid can donate a proton

An acid (HA) reacts with a base (H 2O ) toform the conjugate base of the acid (A-)

and the conjugate acid of base (H 3O +)

HA + H2O = H 3O + + A-

A B C A CBC: conjugate (product) A/B


47/71

Conjugate base/acid

base = proton acceptor

RNH2 + H2O = OH- + RNH3+

B A CB C A


48/71

Measuring Acidity Added acids increase the concentration of

hydronium ion and bases the concentration of hydroxide ion.

In acid solutions [H3O+] > 1 x 1 0-7 M

[OH-]

1 x 1 0-7 M

[H3O+

]

Date post:	29-May-2018
Category:	Documents
Upload:	acabronggo
View:	230 times
Download:	0 times

WATER Rearrange

Documents