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8/8/2019 L09 - 2. Chemistry of Life - Water
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NATS 1610 - 2. Chemistry of Life - Water 1
2. Chemistry of Life Water
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NATS 1610 - 2. Chemistry of Life - Water 2
References
Visualizing Human Biology, Ireland, 2/ed
Chapter 3
Theses notes
Links: http://www.physicalgeography.net/fundamentals/8a.html
http://www.pbs.org/wgbh/nova/mars/essential.html
http://www.youtube.com/watch?v=CT4pURpXkbY&feature=related
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All organisms contain water ~ 70% total body weight
Life originated in liquid water
The biochemical reactions that sustain life need liquid waterin order to operate
To dissolve molecules dissolve
So chemical reactions can occur
When organisms moved to land Carried water with them inside their cells
The physical & chemical properties of liquid water make lifepossible
1. The capacity to dissolve or repel substances
2. Cohesiveness
3. Temperature-stabilizing effects4. Always in flux transports materials
5. In a liquid form over range of temperature from 0-100C
This range allows water molecules to exist as aliquid in most places on our planet
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NONPOLARCovalent Bonds
Usuallyreferred to onlyas covalent bonds
When atoms share electrons equally
i.e., Hydrogen gas (H - H), Methane (CH4)
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POLARCovalent Bonds
Atoms dont share electrons equally
Electrons spend more time near nucleus with most protons
i.e., water and its electrons
oxygen end is slightly negative in charge (electronegative)
hydrogen end is slightly positive in charge
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The HYDROGENBOND is a weak chemical bond
Formed when the slightly positive hydrogen atom of a polar covalent bond
is attracted to
the slightlynegative atom of a polar covalent bond in another molecule (usually)
Water molecule Ammonia molecule
Hydrogen bond
H
HH
H
HO N
http://bcs.whfreeman.com/thelifewire/content/chp02/02020.html
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NATS 1610 - 2. Chemistry of Life - Water 8
hydrogen bond
ammonia
molecule
one
large
molecule
another
large
molecule
a large
molecule
twisted
back
on
itself
H-Bonds
can occur between
different molecules
or within the same
molecule
water
molecule
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Hydrogen Bonding in LiquidWater-molecules held loosely
flows (no spaces)
Hydrogen Bonding in Ice-molecules held tightly
solid (with spaces)
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2.Water is a solvent for other polar
molecules
due to its polarnature
permits chemical reactions
spheres of hydration
hydrophilic
water loving
binds with water
hydrophobic
water hating
repels waterNaCl (sodium chloride)
dissolves in water
1.Water is liquid at room and bodytemperature
other materials are gaseous at these temperatures
can be utilized in world and in body can travel & carry materials
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3.Water is cohesive and adhesive
Due to hydrogen bonds
Water molecules cling to
each other
Water flows and fills things
CapillaryMovement Adhesion to other materials
Excellent transport medium
Surface tension
Water molecules stick tightly toeach other at air interface
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4.Water temperature rises and falls slowly
Highheat capacity i.e., a great deal of heat is required to raise its
temperature because
H-bonds can absorb a lot of energy before they break apart
Takes one calorie of energy to raise the temperature of one gram of
water one degree Celsius
Thus - water holds heat, causing its temperature to drop or rise slowly
Water protects organisms from rapid temp changes
High % of body water in organisms
e.g., 150 lb human is 100 lbs water (~67% body weight)
Resistchanges in body temperature
Keeps relativelystable internal environment
Water in bloodhelps to distribute heat throughout body
heat is picked up from muscles where its generated
Large bodies of water maintain relatively constant temperatures marine life
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5.Waterhas a highheat of vaporization
This is a measure of the amount of heat neededto vaporize the liquid.
a large amount of heat energy, 540calories, is needed to convert 1 gram ofwater to vapor
H-bonds absorb a lot of energy before theybreak apart
Water evaporating from a surface carriesaway heat, cooling the surface
Heat is released from the high energy
stored in the H-bonds of water molecules at
the surface
Body heat is used to evaporate sweat
As sweat evaporates, body is cooled
Prevents body from overheating
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6.Frozen water is less dense than liquid
water
At low temperature water molecules
Move slower Are further apart - frozen water
expands
H-bonding becomes rigid
Spaces between molecules
Less dense ice floats
1 litre of ice weighs less than 1litre of water
A fixed volume of ice has fewer
water molecules than does the
same fixed volume of liquid
water (because the water
molecules are further apart in the
ice and so fewer water
molecules fill that fixed volume of
ice)
Frozen bodies of water
surface ice insulates water below it
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Water, Acids, Bases, pH, & Buffers
Water molecules can dissociate (breaks down) to form hydrogen ions (H+)
andhydroxyl ions (OH-) these in turn can then re-bind to form water
H O H H+ + OH-
The amount ofH+ in the body is preciselyregulated
Slight changes in H+ can cause severe illness bydisrupting chemical
reactions in the body
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Acids & bases defined bywhathappens when each is added to water
Acids
Anything that dissociates in water & releases hydrogen ions (H+)
In water, HCl -- > H+ + Cl-
Acids increase H+ concentration in solution
Bases
Anything that takes up hydrogen ions (H+) & releases hydroxide ions (OH-)when in water
In water, NaOH -- > Na+ + OH- OH- will bind withH+ in water
Bases decrease H+ concentration in solution
pHscale
Measures concentration of H+ & indicates how acidic something is
Buffers
Biological systems function within a verynarrowrange of pH
Help keep the pH within normal limits by
1. Taking up excess H+ when concentrations increase
2. Adding H+ when concentrations decrease
Various buffering systems in body maintain correct body pH levels
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The carbonic acid bicarbonate buffering system
in human blood keep the pH of blood at about 7.4
CO2 + H20 H2CO3 H+ + HCO3
-
Carbon Water CarbonicAcid Hydrogen Bicarbonate
Dioxide Ion Ion
IfH+ levels in blood decrease, carbonic acid will dissociate to release H+ into
the blood
Thus increasing blood H+ levels
IfH+ levels increase, theycombine with the bicarbonate ions to form carbonic
acid which in turn will dissociate into carbon dioxide and water the carbon
dioxide will be exhaled
Thus removing H+ from the blood
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