The Chemistry of Life

Properties of Water

The Water Molecule

•Neutral Charge–All Molecules Are Neutral

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.

(+)

(—)

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 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

CohesionCohesion•The attraction

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

•Allows some insects and spiders to walk on water.

AdhesionAdhesion• Attraction between Attraction between

molecules of different molecules of different substancessubstances

• Responsible for Capillary Responsible for Capillary forces in plantsforces in plants

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

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