waterproperties
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The Extraordinary The Extraordinary Properties of WaterProperties of Water
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WaterWater
•A water molecule (H2O), is made up of threethree atoms --- one oxygen and two hydrogen.
H
HO
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Water is PolarWater is Polar
• In each water molecule, the oxygen atom attracts moreoxygen atom attracts more than its "fair share" of electronselectrons
• The oxygenoxygen end “acts” negativenegative• The hydrogenhydrogen end “acts” positivepositive• Causes the water to be POLARPOLAR• However, Water is neutralneutral (equal
number of e- and p+) --- Zero Net Zero Net ChargeCharge
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Hydrogen Bonds Exist Hydrogen Bonds Exist Between Water MoleculesBetween Water Molecules• Formed between a Formed between a
highly highly Electronegative atom Electronegative atom of a polar molecule of a polar molecule and a and a HydrogenHydrogen
• OneOne hydrogen bond hydrogen bond is is weakweak , but , but manymany hydrogen bonds are hydrogen bonds are strongstrong
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Interaction Between Interaction Between Water MoleculesWater Molecules
Negative Oxygen Negative Oxygen end of one water molecule is end of one water molecule is attracted to the attracted to the Positive Hydrogen Positive Hydrogen end of end of
another water molecule to form a another water molecule to form a HYDROGEN HYDROGEN BONDBOND
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What are What are the the
PropertieProperties of s of
Water?Water?
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Properties of WaterProperties of Water• At sea level, pure water At sea level, pure water boils at boils at
100 °C100 °C and and freezes at 0 °Cfreezes at 0 °C. .
• The The boiling temperature of water boiling temperature of water decreases at higher elevations decreases at higher elevations (lower atmospheric pressure). (lower atmospheric pressure).
• For this reason, an For this reason, an eggegg will take will take longer to boil longer to boil at higher altitudesat higher altitudes
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Properties of WaterProperties of Water
•CohesionCohesion
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Properties of WaterProperties of Water
•CohesionCohesion•AdhesionAdhesion
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Properties of WaterProperties of Water
•CohesionCohesion•AdhesionAdhesion•High Specific HeatHigh Specific Heat
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Properties of WaterProperties of Water
•CohesionCohesion•AdhesionAdhesion•High Specific HeatHigh Specific Heat•High Heat of High Heat of VaporizationVaporization
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Properties of WaterProperties of Water
•CohesionCohesion•AdhesionAdhesion•High Specific HeatHigh Specific Heat•High Heat of High Heat of VaporizationVaporization
•Less Dense as a SolidLess Dense as a Solid
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CohesionCohesion• Attraction between particles of Attraction between particles of
the same substance the same substance (( why water why water is attracted to itself)is attracted to itself)
• Results in Results in Surface tensionSurface tension (a (a measure of the strength of measure of the strength of water’s surface)water’s surface)
• Produces a Produces a surface film surface film on water on water that that allows insects to walk on allows insects to walk on the surfacethe surface of water of water
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Cohesion …Cohesion …
Helps insects walk across water
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AdhesionAdhesion• Attraction between two different Attraction between two different
substancessubstances..• Water will make Water will make hydrogen bonds with hydrogen bonds with
other surfacesother surfaces such as glass, soil, plant such as glass, soil, plant tissues, and cotton. tissues, and cotton.
• CapillaryCapillary actionaction-water molecules will -water molecules will “tow” each other along when in a thin “tow” each other along when in a thin glass tube.glass tube.
• Example: Example: transpirationtranspiration process which process which plants and trees remove water from plants and trees remove water from the soil, and paper towels soak up the soil, and paper towels soak up water.water.
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Adhesion Causes Adhesion Causes Capillary ActionCapillary Action
Which gives water the ability to “climb”
structures
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Adhesion Also Causes Adhesion Also Causes Water to …Water to …
Form spheres & hold onto
plant leaves
Attach to a silken spider
web
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High Specific HeatHigh Specific Heat• Amount of heatAmount of heat needed to raise needed to raise
or lower or lower 1g1g of a substance of a substance 1° C1° C..
• Water Water resistsresists temperature temperature changechange, both for heating and , both for heating and cooling.cooling.
• Water can absorb or release large Water can absorb or release large amounts of heat energy with little amounts of heat energy with little change in actual temperature.change in actual temperature.
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High Heat of High Heat of VaporizationVaporization
• Amount of energy to convert 1g Amount of energy to convert 1g or a substance from a or a substance from a liquid to a liquid to a gasgas
• In order for water to evaporate, In order for water to evaporate, hydrogen bonds must be brokenhydrogen bonds must be broken..
• As water evaporatesAs water evaporates, it removes a , it removes a lot of lot of heatheat with it. with it.
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High Heat of High Heat of VaporizationVaporization
• Water's heat of vaporization is 540 cal/g.540 cal/g.
• In order for water to In order for water to evaporateevaporate, , each gram must each gram must GAIN 540 GAIN 540 calories (temperature doesn’t calories (temperature doesn’t change --- 100change --- 100ooC).C).
• As water evaporatesAs water evaporates, it removes , it removes a lot of a lot of heatheat with it with it (cooling (cooling effect)effect)..
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• Water vapor Water vapor forms a kind of global ‘‘blanket” which helps to keep the Earth warm.
• Heat radiated from the sun Heat radiated from the sun warmed surface of the earth is
absorbed and held absorbed and held
by the vaporby the vapor.
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Water is Less Dense as Water is Less Dense as a Solida Solid
• Ice is less denseIce is less dense as a solid than as a liquid (ice floats)
• Liquid water has hydrogen hydrogen
bonds bonds that are constantly being constantly being
broken and reformed.broken and reformed.
• Frozen waterFrozen water forms a crystal-like crystal-like
latticelattice whereby molecules are set at fixed distances.
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Water is Less Dense as Water is Less Dense as a Solida Solid
•Which is ice and which is Which is ice and which is
water?water?
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Water is Less Dense as a Water is Less Dense as a SolidSolid
WaterWater IceIce
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HomeostasisHomeostasis• Ability to maintain a Ability to maintain a steady state steady state
despite changing conditionsdespite changing conditions• Water is important to this process Water is important to this process
because:because:a. Makes a a. Makes a good insulatorgood insulatorb. Resists temperature changeb. Resists temperature changec. c. Universal solventUniversal solventd. Coolantd. Coolante. Ice protects against temperature e. Ice protects against temperature
extremes ( extremes (insulatesinsulates frozen frozen lakes)lakes)
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Solutions & Solutions & SuspensionsSuspensions
• Water is usually part of a Water is usually part of a mixture.mixture.
• There are two types of There are two types of mixtures:mixtures:– SolutionsSolutions– SuspensionsSuspensions
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SolutionSolution
• Ionic compounds disperse as Ionic compounds disperse as ionsions in waterin water
• Evenly distributedEvenly distributed• SOLUTESOLUTE
– Substance that is being Substance that is being dissolveddissolved
• SOLVENTSOLVENT– Substance into which the solute Substance into which the solute
dissolvesdissolves
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SolutionSolution
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SuspensionsSuspensions
• Substances that don’t dissolve don’t dissolve but separate but separate into tiny pieces.
• Water keeps Water keeps the pieces the pieces suspended suspended so they don’t settle out.
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Acids, Bases and pHAcids, Bases and pHOne water molecule One water molecule in 550 million in 550 million
naturally naturally dissociatesdissociates into a into a Hydrogen Ion Hydrogen Ion (H+) (H+) and a Hydroxide and a Hydroxide Ion Ion (OH-)(OH-)
Hydrogen Ion Hydroxide IonHydrogen Ion Hydroxide Ion Acid Acid BaseBase
H2O H+ + OH-
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The pH ScaleThe pH Scale• Indicates the concentration of Hconcentration of H++
ionsions• Ranges from 0 – 140 – 14• pH of 7 is neutral7 is neutral• pH 0 up to 7 is acid 0 up to 7 is acid … H+ • pH above 7 – 14 is babove 7 – 14 is basic… OH- • Each pH unit represents a factor
of 10X 10X change in concentration• pH 3 is 10 x 10 x 10 (1000) pH 3 is 10 x 10 x 10 (1000)
stronger than a pH of 6stronger than a pH of 6
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AcidsAcids
• StrongStrong Acids Acids have a have a pH of pH of 1-31-3
• Produce Produce lots of lots of H H+ + ionsions
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BasesBases
• Strong Strong Bases Bases have a pH of 11 to 14 11 to 14
• Contain lots of OHlots of OH--
ions ions and fewer H+ ions
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BuffersBuffers• Weak acids or bases that react Weak acids or bases that react
with strong acids or bases to with strong acids or bases to prevent sharp, sudden changes prevent sharp, sudden changes in pH in pH (neutralization).(neutralization).
• Produced naturally by the body Produced naturally by the body to maintain homeostasisto maintain homeostasis
Weak AcidWeak Acid Weak BaseWeak Base
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