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13
GENERALCHEMIST
RY
Water and Properties
right The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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1. gas - particles widely separated,no definite shape or volume solid
2. liquid - particles closer together,definite volume but no definiteshape
3. solid - particles are very closetogether, define shape and definitevolume
1
.2Matterand
Properties
Three States of Matter
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Three States of Water
(a) Solid (b) Liquid (c)Gas
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Comparison of the Three PhysicalStates
1
.2Matterand
Properties
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Polarity of Water
In a water molecule two hydrogen atomsform single polar covalent bonds with anoxygen atom. Gives water more structurethan other liquids
Because oxygen is more electronegative, the
region around oxygen has a partial negativecharge.
The region near the two hydrogen atoms has apartial positive charge.
A water molecule is a polar molecule with
opposite ends of the molecule withopposite charges.
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Water has a variety of unusualproperties because of attractions
between these polar molecules.The slightly negative regions of one
molecule are attracted to the slightly
positive regions of nearby molecules,forming a hydrogen bond.
Each water moleculecan form hydrogen
bonds with up tofour neighbors.
Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 3.1
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HYDROGEN BONDS Hold water molecules
together Each water molecule
can form a maximumof 4 hydrogen bonds
The hydrogen bondsjoining watermolecules are weak,about 1/20th as strongas covalent bonds.
They form, break, andreform with greatfrequency
Extraordinary Propertiesthat are a result ofhydrogen bonds.
Cohesive behavior
Resists changes intemperature
High heat of vaporization
Expands when it freezes
Versatile solvent
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Properties of Water
Polar molecule
Cohesion and
adhesion High specific heat
Density greatest
at 4oC Universal solvent
of life
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Organisms Depend onCohesion
Cohesion is responsible forthe transport of the watercolumn in plants
Cohesion among watermolecules plays a key role inthe transport of water againstgravity in plants
Adhesion, clingingof one substance toanother, contributestoo, as water adheresto the wall of the
vessels.
Hydrogen bonds hold the
substance together, aphenomenon called cohesion
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Surface tension, a measure of theforce necessary to stretch or break
the surface of a liquid, is related tocohesion.
Water has a greater surface tension than
most other liquids because hydrogenbonds among surface water moleculesresist stretching or breaking the surface.
Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 3.3
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Moderates Temperatures onEarth
Celsius Scale at Sea Level
100oC Water boils
37oC Human body
temperature
25oC Room temperature
0oC Water freezes
Water stabilizes air temperatures by absorbing heat fromwarmer air and releasing heat to cooler air.
Water can absorb or release relatively large amounts of heatwith only a slight change in its own temperature.
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Three-fourths of the earthis covered by water. Thewater serves as a largeheat sink responsible for:
1. Prevention oftemperature fluctuations
that are outside therange suitable for life.
2. Coastal areas having amild climate
3. A stable marine
Specific Heat is the amount of heat that mustbe absorbed or lost for one gram of a
substance to change its temperature by 1oC.
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Evaporative Cooling
The cooling of a surface occurswhen the liquid evaporates
This is responsible for:
Moderating earths climate
Stabilizes temperature in aquaticecosystems
Preventing organisms fromoverheating
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Density of Water Most dense at 4oC
Contracts until 4oC
Expands from 4oC to 0oC
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Most biochemical reactions involve solutesdissolved in water.
There are two importantquantitative proprieties of
aqueous solutions.
1. Concentration
2. pH
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