The Chemistry of Life

Properties of Water

Water is the single most abundant substance on Earth!

What are What are the the

PropertieProperties of s of

Water?Water?

Water is Water is different different

than other than other substances – substances – it expands it expands

as it freezes!as it freezes!

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

WaterWater

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

H

HO

Nicknamed “Mickey Mouse Molecule”

The Water Molecule•Neutral Charge

–All Molecules of Water are Neutral–Equal number of e- and p+

Water

•Water is

polar!

The Water MoleculeThe Water Molecule• PolarityPolarity

– A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.

(+)(-)

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• Remember, Water is neutralneutral

(equal number of e- and p+) --- Zero Net ChargeZero Net Charge

Hydrogen BondsHydrogen Bonds• Polar water molecules Polar water molecules act like act like

magnetsmagnets and attract each other and attract each other • Hydrogen BondsHydrogen Bonds

– The attraction of the Hydrogen end The attraction of the Hydrogen end (+) of one molecule for the Oxygen (+) of one molecule for the Oxygen end end (-)(-) of another water molecule. of another water molecule.

– They are the They are the strongest bondsstrongest bonds that that can form can form betweenbetween moleculesmolecules

– OneOne hydrogen bond is hydrogen bond is weakweak, but , but manymany hydrogen bonds are hydrogen bonds are strongstrong

Hydrogen BondsHydrogen Bonds• Negative Oxygen Negative Oxygen

end of one water end of one water molecule is molecule is attracted to the attracted to the Positive Positive Hydrogen Hydrogen end of end of another water another water molecule to form molecule to form a a HYDROGEN HYDROGEN BONDBOND

•Water is cohesive!

CohesionCohesion•The attraction between

molecules of the same substance (e.g. water).

• 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 surface film on water Produces a surface film on water that allows many drops of water that allows many drops of water to be on top of one penny and to be on top of one penny and insects to walk on the surface of insects to walk on the surface of waterwater

Cohesion …Cohesion …

Helps insects walk across water

Cohesion …Cohesion …

How many drops did you get on your

penny?

AdhesionAdhesion• Attraction between Attraction between

molecules of different molecules of different substancessubstances

• Adhesion between water and Adhesion between water and plants is Responsible for plants is Responsible for Capillary forces in plantsCapillary forces in plants

Capillary ActionCapillary Action• CapillaryCapillary actionaction-water -water

molecules will “tow” each molecules will “tow” each other along when in a thin other along when in a thin glass tube.glass tube.

• Example: Example: transpirationtranspiration process process which plants and trees remove which plants and trees remove water from the soil, and paper water from the soil, and paper towels soak up water.towels soak up water.

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

Form spheres & hold onto plant

leaves

Attach to a silken spider web

Adhesion Causes Adhesion Causes Capillary ActionCapillary Action

Which gives water the ability to “climb”

structures

Try it!

High Specific HeatHigh Specific Heat• Amount of heatAmount of heat needed to raise or needed to raise or

lower lower 1g1g of a substance of a substance 1° C1° C..

• Water Water resistsresists temperature changetemperature change, , both for heating and cooling.both for heating and 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 1g or Amount of energy to convert 1g or a substance from a a substance from a liquid to a gasliquid to a gas

• 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.

• 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 and constantly being broken and

reformed.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 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 mixturemixture..

• There are two types of There are two types of mixtures:mixtures:– SolutionsSolutions– SuspensionsSuspensions

SolutionSolution• Ionic compounds disperse as Ionic compounds disperse as

ions in waterions in water• Evenly distributedEvenly distributed• SOLUTESOLUTE

– Substance that is being Substance that is being dissolveddissolved

• SOLVENTSOLVENT– Substance into which the Substance into which the

solute dissolvessolute dissolves

SolutionSolution

SuspensionsSuspensions• Substances that Substances that

don’t dissolve don’t dissolve but separate but separate into tiny pieces.into tiny pieces.

• Water keeps Water keeps the pieces the pieces suspended so suspended so they don’t they don’t settle out.settle out.

Acids, Bases & pHAcids, Bases & pH• 1 water molecule in 550 million 1 water molecule in 550 million

naturally dissociates into a naturally dissociates into a Hydrogen IonHydrogen Ion and a and a Hydroxide IonHydroxide Ion

Hydrogen Ion Hydroxide IonHydrogen Ion Hydroxide Ion Acid Acid BaseBase

H2O H+ + OH-

The pH ScaleThe pH Scale• Indicates the concentration of H+

ions• Ranges from 0 – 14• pH of 7 is neutral• pH 0 – 6.99 is acid … H+ • pH 7.01 – 14 is basic… OH- • Each pH unit represents a factor

of 10 change in concentration

Acids and Bases

• pH Scale indicates the concentration of H+ ions

• Ranges from 0 – 14• pH of 7 is neutral• pH 0 – 6.99 is acid …

H+ • pH 7.01 – 14 is

basic… OH- • Each pH unit

represents a factor of 10 change in concentration

AcidsAcids•Strong

Acid = pH 1-3

H+ ions

BasesBases•Strong

Base = pH 11 – 14 OH-ions

BuffersBuffers• Weak acids or bases that Weak acids or bases that

react with strong acids or react with strong acids or bases to prevent sharp, bases to prevent sharp, sudden changes in pH.sudden changes in pH.

Weak AcidWeak Acid Weak BaseWeak Base

Acid Rain• Rain, snow or fog with more strongly acidic than

pH of 5.6• West Virginia has recorded 1.5• East Tennessee reported 4.2 in 2000• Occurs when sulfur oxides and nitrogen oxides

react with water in the atmosphere– Lowers pH of soil which affects mineral

solubility – decline of forests– Lower pH of lakes and ponds – In the

Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.

Now – Summarize your notes!

Quiz next time!