Post on 28-Dec-2015
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!