The Extraordinary The Extraordinary Properties of WaterProperties of Water

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 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

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

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

What are What are the the

PropertieProperties of s of

Water?Water?

Properties of WaterProperties of Water

•Boiling/Freezing Point of Boiling/Freezing Point of WaterWater

•CohesionCohesion•AdhesionAdhesion•High Specific HeatHigh Specific Heat•Less Dense as a SolidLess Dense as a Solid

Boiling and Freezing Boiling and Freezing Point of WaterPoint 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

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

Cohesion …Cohesion …

Helps insects walk across water

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.

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.

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.

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 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)

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