The Extraordinary The Extraordinary Properties of WaterProperties of Water

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Draw the Water Draw the Water MoleculeMolecule

WaterWater

•A water molecule (H2O), is made up of threethree atoms --- one oxygen and two hydrogen.

H

HO

Water is PolarWater is Polar• In each water molecule, the oxygen atom oxygen atom

attracts moreattracts 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 a neutral molecule neutral molecule

because it has equal number of protons because it has equal number of protons and electrons.and electrons.--- Zero Net ChargeZero Net Charge

• Water is called a polar molecule because the oxygen end acts negatively charged an the hydrogen end acts positively charged.

Hydrogen Bonds Exist Hydrogen Bonds Exist Between Water MoleculesBetween Water Molecules• OneOne hydrogen bond hydrogen bond

is is weakweak , but , but manymany hydrogen bonds are hydrogen bonds are strongstrong

Interaction Between Interaction Between Water MoleculesWater Molecules

HOW HYDROGEN BONDS FORM: HOW HYDROGEN BONDS FORM: 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

What are What are the the

PropertieProperties of s of

Water?Water?

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

Properties of WaterProperties of Water

•CohesionCohesion

Properties of WaterProperties of Water

•CohesionCohesion•AdhesionAdhesion

Properties of WaterProperties of Water

•CohesionCohesion•AdhesionAdhesion•High Specific HeatHigh Specific Heat

Properties of WaterProperties of Water

•CohesionCohesion•AdhesionAdhesion•High Specific HeatHigh Specific Heat•High Heat of High Heat of VaporizationVaporization

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

CohesionCohesion• Attraction between particles of the Attraction between particles of the

same substance same substance (( why water is why water is attracted to itself)attracted to itself)

• Cohesion produces Surface tension Cohesion produces Surface tension when one water molecule attracts when one water molecule attracts other water molecules. other water molecules. (a measure of (a measure of the strength of water’s surface)the strength of water’s surface)

• Produces a Produces a surface film surface film on water that on water that allows insects to walk on the surfaceallows insects to walk on the surface of of water water

Cohesion …Cohesion …

Helps insects walk across water

AdhesionAdhesion• Attraction between Attraction between two different two different

substancessubstances. Cohesion is the attraction . Cohesion is the attraction between water molecules. between water molecules.

• Water will make Water will make hydrogen bonds with hydrogen bonds with other surfacesother surfaces such as glass, soil, such as glass, soil, plant tissues, and cotton. plant 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.

Adhesion Causes Adhesion Causes Capillary ActionCapillary Action

Which gives water the ability to “climb”

structures

Adhesion Also Causes Adhesion Also Causes Water to …Water to …

Form spheres & hold onto

plant leaves

Attach to a silken spider

web

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.

High Heat of High Heat of VaporizationVaporization• Amount of energy to convert Amount of energy to convert

1g of a substance from a 1g of a substance from a liquid liquid to a gasto a gas

• In order for water to In order for water to evaporate, evaporate, hydrogen bonds hydrogen bonds must be brokenmust be broken..

• As water evaporatesAs water evaporates, it , it removes a lot of removes a lot of heatheat with it. with it.

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)..

• 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.

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 bonds hydrogen bonds that are constantly being broken constantly being broken

and reformed.and reformed.

• Frozen waterFrozen water forms a crystal-like crystal-like

latticelattice whereby molecules are set at fixed distances.

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?

Water is Less Dense as a Water is Less Dense as a SolidSolid

WaterWater IceIce

HomeostasisHomeostasis• Ability to maintain a Ability to maintain a steady state steady state

despite changing conditionsdespite changing conditions• Water is important to this Water is important to this

process because:process 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 e. Ice protects against

temperature temperature extremes extremes ((insulatesinsulates frozen lakes) frozen lakes)

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

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

SolutionSolution

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.

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-

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

AcidsAcids

• StrongStrong Acids Acids have a have a pH of pH of 1-31-3

• Produce Produce lots of lots of H H+ + ionsions

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

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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