Properties of Water

A compound is a pure substance made up of atoms of two or more elementsThe proportion of atoms

are always fixedChemical formula shows

the kind and proportion of atoms of each element that occurs in a particular compound

Molecules are the simplest part of a substance that retains all of the properties of the substance and exists in a free state

Some molecules are large and complex

Chemical FormulasChemical FormulasSubscript after a symbol tell the number

of atoms of each elementH20 has 2 atoms of hydrogen & 1 atom

of oxygenCoefficients before a formula tell the

number of molecules3O2 represents 3 molecules of oxygen or

(3x2) or 6 atoms of oxygen

The extraordinary properties of Water

•At sea level, pure water boils at 100 °C and freezes at 0 °C.

•The boiling temperature of water decreases at higher elevations (lower atmospheric pressure). •For this reason, an egg will take longer to boil at higher altitudes.

The Water Molecule

Neutral ChargeAll Molecules Are Neutral

The Water MoleculeThe Water MoleculePolarityPolarity

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

(+)

(—)

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

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

Hydrogen BondsHydrogen Bonds

CohesionCohesionThe attraction between molecules of the same substance (e.g. water).

Allows some insects and spiders to walk on water.

AdhesionAdhesionAttraction between Attraction between molecules of different molecules of different substancessubstances

Responsible for Capillary Responsible for Capillary forces in plantsforces in plants

High Specific Heat

•Water resists temperature change, both for heating and cooling.

•Water can absorb or release large amounts of heat energy with little change in actual temperature.

Homeostasis

Steady stateConstant physiological condition of cells,

organisms global ecosystemsa. Makes a good insulatorb. Resists temperature changec. Universal solventd. Coolante. Ice protects against temperature

extremes

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:SolutionsSolutionsSuspensionsSuspensions

SolutionSolutionIonic compounds disperse as Ionic compounds disperse as

ions in waterions in waterEvenly distributedEvenly distributedSOLUTESOLUTE

Substance that is being Substance that is being dissolveddissolved

SOLVENTSOLVENTSubstance into which the Substance into which the solute dissolvessolute dissolves

SolutionSolution

SuspensionsSuspensionsSubstances 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 settle they don’t settle out.out.

Acids, Bases & pHAcids, Bases & pH1 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 ScaleIndicates the concentration of H+ ions

Ranges from 0 – 14pH of 7 is neutralpH 0 – 6.99 is acid … H+ pH 7.01 – 14 is basic… OH- Each pH unit represents a factor of 10 change in concentration

AcidsAcidsStrong Acid = pH 1-3

H+ ions

BasesBasesStrong Base = pH 11 – 14 OH-ions

BuffersBuffersWeak 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