The Chemistry of Life

Properties of Water

2.2

The Water Molecule

• Neutral Charge – ZERONeutral Charge – ZERO•Have no charge•Have an Equal number of p+ and e-•Charges aren’t evenly distributed

The Water MoleculeThe Water Molecule• PolarityPolarity

– A water molecule is polar because there is an uneven distribution of uneven distribution of electronselectrons 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 of another water molecule.water molecule.

• They are bonds that They are bonds that form form between moleculesbetween molecules ( (COCO22, H, H22O)O)

Hydrogen BondsHydrogen Bonds

CohesionCohesion• The attraction

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

• HH22O attracting other O attracting other HH22O moleculesO molecules

• Allows some insects and spiders to walk on water.

Basilisk Lizard and Water Strider

• http://www.youtube.com/watch?v=45yabrnryXk• http://www.youtube.com/watch?

v=RphuMEUY3Og

Adhesion & CapillarityAdhesion & Capillarity• AdhesionAdhesion - Attraction between - Attraction between

HH22O molecules and different O molecules and different moleculesmolecules

• How can you demonstrate this? How can you demonstrate this? Think!Think!

• Cohesion & adhesion produceCohesion & adhesion produce CapillarityCapillarity (upward movement (upward movement against gravity of water through against gravity of water through small tubes)small tubes)

Question: How do Question: How do plants make use plants make use of Capillarity?of Capillarity?

Capillary Action

• Helps plants draw up water against gravity: http://www.youtube.com/watch?v=y-h_qGhgtno

Heat Capacity/Specific Heat

• H-bonds cause water to stick together—takes a lot of energy to make molecules move faster/heat up– Water resists temperature change—no

wide fluctuations in temperature– Temperature moderation

• large bodies of water (environment) • inside organisms

Solutions & Solutions & SuspensionsSuspensions

• Water is usually part of a Water is usually part of a mixturemixture..

• Because so many things dissolve Because so many things dissolve in water, it is called the in water, it is called the Universal SolventUniversal Solvent

• There are two types of mixtures:There are two types of mixtures:– Solutions—dissolved particlesSolutions—dissolved particles– Suspensions—undissolved Suspensions—undissolved particlesparticles

Properties of SolutionsProperties of Solutions• Ionic compoundsIonic compounds disperse as disperse as ionsions

in water (+ions & -ions spread out in water (+ions & -ions spread out among polar water molecules)among polar water molecules)

• Solutions are Solutions are Evenly distributedEvenly distributed mixturesmixtures

• SOLUTE SOLUTE Substance that is being Substance that is being dissolved (ex. water)dissolved (ex. water)

• SOLVENT SOLVENT Dissolving Substance for Dissolving Substance for the solute (ex. salt)the solute (ex. salt)

Ionic SolutionsIonic Solutions

Na+ ions will be attracted to WHAT END of the water molecule?

NaCl solution animation

• http://www.youtube.com/watch?v=EBfGcTAJF4o

SuspensionsSuspensions• Substances that Substances that

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

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

• Blood & Blood & CytoplasmCytoplasm are are suspensionssuspensions

Blood—solution AND suspension

pH Scale

• Draw and label from textbook.• Song: http://www.youtube.com/watch?v=zTLiJE-

j1-I

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 Hydroxide IonIon

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 up to 7 acid … H+ • pH above 7 to 14 base… OH- • Each pH unit represents a factor

of 10X change in concentrationHow much stronger is a pH3 than a How much stronger is a pH3 than a

pH of 5?pH of 5?

AcidsAcids•Strong

Acid = pH 1-3

•High in H+

ions•Lower

number of OH- ions

BasesBases•Strong Base

= pH 11 – 14•High in OH-

ions•Lower in

number of H+ ions

BuffersBuffers• Weak acids or basesWeak acids or bases that react that react

with strong acids or baseswith strong acids or bases• Made by the bodyMade by the body• Prevent sharp, sudden changes in Prevent sharp, sudden changes in

pH pH (keep pH neutral)(keep pH neutral)

Weak AcidWeak Acid Weak BaseWeak Base

Buffers cont.

• Human body: 6.5-7.5• Blood: 7.4• Buffers dissolved in

organisms’ aqueous environment help maintain homeostasis.

Animations

• Hydrogen bonding: www.classzone.com

Assessment

• Draw 3 molecules of water. Show polarity and hydrogen bonding. Make sure to orient the molecules correctly.

• Complete the 2.2 assessment in your text.• Go to www.classzone.com and practice—games

or practice quizzes.